Parasitology

1. NUB1106: Microbiology and
Parasitology
UNIT2: Parasitology: Filariasis

2. Filaria and filariasis
 These nematodes are known as filariae and consist of a group of
nematodes which have successfully invaded the blood stream,
connective tissue or serous cavities of vertebrates.
 Many of them are of medical and veterinary importance attacking
man and various domestic animals being transported by various
vectors, including mosquitoes.
 The nematodes from this order require intermediate hosts for the
completion of their life cycle.
 Sexually mature female worms release microfilaria, which are pre-
larval stages. These are released into the bloodstream.
 Most species are known to be ovoviviparous and some have
‘sheathed’ microfilaria other not sheathed.

3. Filaria and filariasis
 The filarial nematodes which parasitize man consist of Wuchereria
bancrofti, Loa loa, Onchocerca volvulus.
 They inhabit a range of locations within the body; lymph glands,
deep connective tissue, subcutaneous tissues or mesenteries.
 It has been estimated that approximately one billion people in
tropical and subtropical countries are exposed to the risk of filarial
infections and at least 200 million are infected with filariasis.
 The species which are primarily responsible for these human
filarial infections are Wuchereria bancrofti and Onchocerca
volvulus.

4. Wuchereria bancrofti
Introduction
 There are two strains of W. bancrofti;
1. The nocturnal periodic strain which is widely distributed in endemic regions (i.e.
Africa, India and the Far East and also parts of China, Korea and Japan) with the
microfilariae being in their highest concentrations between the hours of 10pm and
2am.
2. The sub-periodic strain which is found in the Pacific region, and has a
microfilaremia all the time with the highest numbers being detected between noon
and 8pm.
 Humans are the only known reservoir host of W. bancrofti. Infection rates in
some communities in East Africa exceed 30% of adults causing swellings of the
legs or genital system, known as elephantiasis in man.
 The main vector is Culex quinquefasciatus, a mosquito that is particularly
common in towns. In rural areas throughout Africa, Anopheles gambiae and
Anopheles funestus are involved in transmission.

5. Wuchereria bancrofti
Morphology
 The adult worms are white and threadlike.
 The male measures between 2.5–4cm whereas the female is
larger, measuring between 8-10cm.
 The microfilariae are 230-275μm in length.
 The tail of the microfilariae of W. bancrofti tapers to a delicate
point and exhibits no terminal nuclei.
 The sheath the microfilariae of W. bancrofti stains with
hematoxylin stain.

6. Wuchereria bancrofti
Life Cycle
 Microfilariae enter the host during a blood meal when the vector, a
mosquito, punctures the skin.
 The infective larvae enter through the wound and migrate to the
peripheral lymphatics where they grow to mature male and female
worms. They can live there for several years.
 After mating, the gravid females release sheathed microfilariae into the
peripheral blood where they can be detected 8-12 months after the initial
infected bite.
 The mosquito acquires the infection by ingestion of the microfilaria in the
blood meal.
 The microfilariae lose their sheath on arrival in the stomach of the
mosquito due to gastric juices.

7. Wuchereria bancrofti
Life Cycle
 The larvae migrate to the thoracic muscles and develop into
infective larvae over a period of 6-14 days.
 The larvae then migrate to the mouthparts of the mosquito
which infects the host during a blood meal.
 The blood stages of filariae, microfilariae, vary in the times
when they are present in the peripheral blood, corresponding
with the peak biting time of the vector.
 Thus, in nocturnally periodic forms the microfilaria are present
in the peripheral blood circulation at night; during the day they
reside in the deep tissues, particularly the lungs.

8. Wuchereria bancrofti

9. Wuchereria bancrofti

10. Wuchereria bancrofti
 High eosinophilia, high IgE level and high anti-filarial antibody
titers and wheeze and cough are features of this syndrome.
Laboratory Diagnosis
 Sheath may or may not stain with Giemsa; does stain with
hematoxylin stains.
 Empty space between the nuclei and the body wall.
 No nuclei in tip of tail.
 Inner body is rarely visible in Giemsa.
 Tip of tail may be bent underneath the body.
 Microfilaria is found in blood.

11. Loa loa
Introduction
 Loa loa, also known as the African eye worm, is a filarial
nematode endemic in the rain forests of West and Central
Africa.
 It is transmitted by Chrysops species, also known as mango
flies or horse flies and humans are the only known reservoir.
 It is estimated that 2-13 million humans are infected with the
larvae.
 Adults migrate in the subcutaneous tissues of man and
monkeys, with them eventually migrating across the eyeball
under the conjunctiva.

12. Loa loa
Morphology
 Adult males of Loa loa are 2–3.5cm long and the females from
5-7cm.
 The microfilariae of Loa loa are 250-300μm.
 They possess a sheath.
 The sheath does not stain with Giemsa. The tail gradually
tapers to a rounded end, the densely packed nuclei extending
to the tip.

13. Loa loa

14. Loa loa
Life cycle:
 The adult worms live in the subcutaneous and deep connective
tissues and the microfilariae are found in the peripheral blood,
where they can be in ingested by the Chrysops fly (day biting fly)
 The adults can live in the tissues for up to 17 years.
 Once the microfilariae have been taken up by the Chrysops during a
blood meal they develop within the fat body.
 The microfilariae, L3 reenter the hosts blood stream when the fly
takes another blood meal. They reach adult worms within 4- 6
months living in the subcutaneous and deep connective tissues.
 The microfilariae exhibit diurnal periodicity, the highest numbers
being detected in blood between 10am and 2pm.

15. Loa loa
Laboratory Diagnosis
 Kinked and sheathed microfilaria.
 Sheath does not stain with Giemsa stain; does stain with
hematoxylin stains.
 Nuclei crowded extending to tip of tail; tip of tail tapers.
Cephalic space as long as it is broad. Inner body does not
usually stain.
 The microfilaria are found in blood.

16. Microfilaria Worms Found in Tissue and
Skin
 The main species of microfilariae found in the skin and tissue
are Onchocerca volvulus and Mansonella streptocerca.
 Microfilariae of Onchocerca volvulus and less often,
Mansonella streptocerca migrate through the dermis causing
itching and skin texture changes and occasionally arrive in the
eye where they cause blindness.
 Detection of these microfilariae is from skin snips or nodule
biopsies.
 When high numbers of microfilariae are present, they can
occasionally be found in the blood and urine.

17. Onchocerca volvulus
Introduction
 Onchocerca volvulus is mainly found in West Africa and Central and South
America.
 Onchocerciasis, also known as river blindness, is a major public health
problem, especially in West Africa despite the fact that an eradication program
has been established.
 It is one of the world’s most distressing diseases of helminth origin, often
resulting in blindness.
 Onchocerca volvulus is transmitted by the species Simulium or black fly whose
breeding habitat is by fast flowing rivers or streams, therefore it is mostly seen
where water courses are. The adult worms are found in nodules or
onchodermata in superficial sites, but may invade other tissues.
 It is estimated that there are 18 million cases worldwide with 17.5 million being
found in Africa. Nigeria is the most infected region. The rate of morbidity is high
in relation to those with an infection.

18. Onchocerca volvulus
 Transmitted directly into the hosts bloodstream.
 The sexually mature female worms release microfilariae which
migrate out from the nodules into the skin and other tissues, most
significantly into the eye.
Morphology
 The whitish adult worm lies coiled within capsules in the fibrous
tissue.
 The female can measure up to 50cm while the males are shorter
measuring up to 5 cm.
 The microfilariae of O. volvulus are unsheathed and are usually
found in the dermis.
 They measure between 221-287μm long

19. Onchocerca volvulus
 The life cycle is similar to W. bancrofti, except that the
intermediate hosts are various species from the genus Simulium
(Black flies).
 The microfilariae are ingested by a Black fly during a blood
meal, from where they are carried to the midgut where they
penetrate the epithelium and migrate, via the hemocoele.
 Here they undergo two molts, L1–L3 and develop into infective
L3 larvae which move to the mouth parts. Development is
completed in 6–9 days.
 When the infected fly takes another blood meal the infective
larvae are once again transmitted into another host (definitive
host).

20. Onchocerca volvulus

21. Onchocerca volvulus
Clinical Disease
 Clinical manifestations are due to microfilariae in the epidermis.
 Light infections may be asymptomatic or cause pruritis. This leads to
scratching which can result in infection.
 Lyphadenopathy may also be a feature of early infection. After months or
years, onchodermatitis results in secondary stage of thickening due to
intradermal edema and pachydermis.
 There is a loss of elastic fibers resulting in hanging groin, hernias and
elephantiasis of the scrotum.
 There is mottled depigmentation of the skin. Ocular lesions include
secondary glaucoma and cataract, coroidoretinitis and corneal opacities.
The major complication of onchocerciasis is the development of lesions
in the eye which may result in blindness.

22. Laboratory Diagnosis of Onchocerca
volvulus
Analysis of Skin Snips:
 Small amounts of skin are collected by using a needle to raise the skin
and then to slice about 1mg of skin to a depth of 0.5μm. Snips are
collected from several sites, usually the shoulders or the buttocks and
sometimes the chest.
 The snips are placed immediately in 0.5ml normal saline in a microtiter
plate and left for 4 hours to allow the microfilariae to migrate out of the
tissues. After four hours, the wells are examined using a microscope.
 The microfilariae should still be moving.
 The preparation may be stained with Giemsa at pH 6.8
 Observation:Thick microfilaria. Does not have a sheath. Nuclei do
not extend to tip of tail. The microfilaria are found only in skin.

23. Dracunculus medinensis
Introduction
 Dracunculus medinensis is a non-filarial parasite as it only has one
uterus whereas filaria have two.
 It is usually associated with places where there is a lack of clean
drinking water e.g. wells, covered cisterns, ponds.
 The life cycle usually involves copepod intermediate host.
 They are parasitic in the connective tissue or coelom of vertebrates.
 The disease associated with this parasite is known as
Dracunculiasis.
Morphology
 The adult female worm measure up to one meter in length whereas
the male measures about 2cm.

24. Life cycle of Dracunculus medinensis
 Mature female worms which are gravid with microfilariae migrate to the
superficial layers of skin of humans, especially those regions which are
most likely to come in contact with water, such as the ankle, foot, arms
and shoulders.
 Here the worms secrete a substance which causes a blister to rise over, the
blister eventually forms into an ulcer containing hundred of active larvae,
then blister on contact with water break and larvae are released.
 If the microfilariae are ingested by an appropriate species of Cyclops,
they break though the soft mid-intestine wall and come to lie in the body
cavity.
 The larvae undergo two molts and become infective in approximately
three weeks. Humans become infected by accidentally by drinking water
with infective Cyclops. Upon ingestion the larvae are activated to
penetrate through the gut wall, and migrate through the tissues, molting
twice and finally become adults

25. Life cycle of Dracunculus medinensis

26. Dracunculus medinensis
Clinical Disease
 After ingestion of the Cyclops, there is no specific pathology
associate with the mucosal penetration and larval maturation in the
deep connective tissues.
 Erythema and tenderness can be associated with blister formation.
 The patient can also exhibit vomiting, diarrhea, asthmatic attacks.
Symptoms usually subside when the lesion erupts. If the worm is
removed, healing usually occurs without any problems.
 If the worm is damaged or broken during removal, there may be
intense inflammatory reaction with possible cellulitis along the
worms migratory tract.

27. Mechanical Removal of Dracunculus medinensis

28. Dracunculus medinensis
Laboratory Diagnosis
 The best remedy for removing the adult worm is a slow
process of daily gently rolling the worm around a small stick
and slowly pulling it out of the skin.
 With this method you must be careful not to pull apart the worm
as it will recoil back into the skin and cause secondary infections.
 The program includes stopping people from drinking infected
water, educating the communities about the parasite, and adding
chemical to the water to kill it off.

29. NUB1106: Microbiology and
Parasitology
UNIT2: Parasitology:Helminthes

30. Identifying Intestinal Helminths
 There are three groups of medically important helminths;
Cestodes (tapeworms), Nematodes (roundworms) and
Trematodes (flukes).
 These parasites live in both the body spaces (gut lumen, bile
ducts, lungs, etc.) and in tissues (blood, muscles and skin).
 The usual diagnostic stages for identifying medically
important helminths are the eggs and larvae. Occasionally,
adult worms like Ascaris and Enterobius may be seen and
segments or proglottids are used for diagnosing certain
tapeworms.

31. Identifying Intestinal Helminths
 If an egg, is found with the following features:
1. Size: The length and width are measured and are generally within a
specific range.
2. Shape: Each species has its own particular shape.
3. Stage of development when passed: In some species, the eggs consist of
a single cell; in some, there may be several cells; and some species are
usually embryonated when passed in the feces.
4. Thickness of the egg shell: Some species, like Ascaris, have thick shells;
others, like hookworm, have thin shells.
5. Color: Some eggs are colorless (e.g., hookworm, Enterobius), others are
yellow or brown (Ascaris, Trichuris).
6. Presence of characteristic like opercula (lids), spines, plugs, hooklets, or
mammillated outer coats.

32. Cestodes(Taenia species)
 The cestodes (or tapeworms) form a group of worms, exhibiting two
unmistakable morphological features; they all possess flat, and lack an
alimentary canal.
 Adult tapeworms usually inhabit the alimentary canal of their hosts and
attach themselves to the mucosa by means of a scolex.
 This lack of an alimentary canal markedly separates tapeworms from
nematodes and trematodes.
 The body consists of a chain of segments or proglottids, which can be
immature, mature or gravid; the latter of which contain a fully developed
uterus packed with eggs.
 Cestode are monoecious(hermaphrodite)
 Except for Hymenolepis nana, which can develop directly in the same
host, the lifecycle of tapeworms involves both an intermediate and
definitive host.

33. Cestodes(Taenia species)
Introduction
 Taenia species are the most common cestode parasites of humans.
 More than 60 million people are infected with T. saginata (beef
tapeworm) world wide and about four million are infected with T.
solium (pork tapeworm).
 T. saginata has a cosmopolitan distribution, but is more common
in developing countries where hygiene is poor and the inhabitants
have a tendency of eating raw or insufficiently cooked meat.
 T saginata is the most common adult tapeworm found in man.

35. Cestodes(Taenia species)
 Both humans and cattle or pigs are necessary to the complete
life cycle of Taenia species. Eggs ingested by the intermediate
hosts usually contain oncospheres.
 The oncospheres then hatch out in the duodenum, pass into the
intestine where they penetrate the intestinal wall and are then
carried by the circulation to be deposited in tissues (usually
muscle).

36. Cestodes(Taenia species)
 There they develop into cysticerci larva.Humans become
infected by ingesting inadequately, cooked beef or pork with
cysticerci, containing an invaginated protoscolex.
 The protoscolexes evaginate and pass into the small intestine
where they attach themselves to the mucosa and develop into
adult worms.
 Eggs and proglottids are passed out in the feces, and are then
eaten by the intermediate host, thus, perpetuating the life
cycle.

37. Cestodes(Taenia species)
Morphology
 Ova of Taenia species are spherical, yellowish brown and measure
31-34μm in diameter.
 The shell is thick and radially striated. Within the shell, the
oncosphere has 3 pairs of hooklets.
 The length of the adult T. saginata is 4-8 meters long and that of T.
solium is 3-5 meters long.
 If the scolex is recovered, the four suckers and rostellum of
hooklets of T. solium will distinguish it from T. saginata, which has
four suckers but no hooklets.

38. Cestodes(Taenia species)
Head( scolex) of taenia
 If the scolex is recovered,
the four suckers and
rostellum of hooklets of T.
solium will distinguish it
from T. saginata, which has
four suckers but no
hooklets.

39. Cestodes(Taenia species)
Egg of taenia spp
Adult worm of taenia
spp

40. Cestodes(Taenia species)
Clinical Disease
 The presence of the adult worm rarely causes symptoms apart from
slight abdominal irritation with diarrhea, constipation or indigestion.
 The accidental ingestion of the embryonated ova of T. solium may result
in cysticercosis(neurocysticercosis) in man.
 An infection due to an adult Taenia, in man or animals, is referred to as
taeniasis.
 T. saginata (the beef tapeworm) does not cause human cysticercosis.
When the embryonated eggs are ingested, the embryos hatch out,
migrate through the intestinal wall and are carried around the body in
the circulation and deposited in various tissues.
 Human cysticercosis is usually asymptomatic unless the infection is
particularly heavy.

41. Difference between T. saginata and T. solium
Characteristic Taenia saginata Taenia solium
Intermediate host cattle pig
Site of development Muscle, viscera Brain, skin, muscle
Scolex: adult worm No hooks Hooks present
Scolex: cysticercus No rostellum Rostellum and hooks
present
Proglottids: Uterine
branches
23 (14 – 32) 8(7-11)

42. Cestodes(Taenia species)
Laboratory Diagnosis
 Diagnosis of intestinal taeniasis can be made by recovery of
the characteristic ova in the stool.
 However, the ova of T. solium and T. saginata are identical and
diagnosis may be also made by the recovery of the segments
or scolex.
 MRI(Magnetic Resonance Imaging) scans may reveal the
presence of lesions in the brain(in case of Taenia solium)

43. Hymenolepis nana
Introduction
 Hymenolepis nana, the dwarf tapeworm, is the smallest tapeworm
to infect humans.
 This cestode belongs to a large family known as Hymenolepididae.
 The diagnostic features of this family are: scolex armed with one
circlet of five hooks.
 Hymenolepis nana has a cosmopolitan distribution and is thought
to be the most common tapeworm throughout the world.
 The infection is more frequently seen in children although adults
are also infected, causing hymenolepiasis.
 The lifecycle of H. nana does not require an intermediate host,
complete development occurring within a single host.

44. Life Cycle

45. Hymenolepis nana
 The eggs that are released from mature proglottids in the upper ileum are
usually passed out in the feces. If swallowed by another human they
develop into hexacanth oncospheres and burrow into the villi of the small
intestine.
 The eggs which are ingested by insects, such as fleas, beetles or
cockroaches hatch to form tailed cysticercoids which remain unmodified
as long as they are inside the insect.
Morphology
 The egg containing the oncosphere bears three pairs of hooklets and is
surrounded by a membrane.

46. Hymenolepis nana
 The adult tapeworm is normally 2.5-4cm long. The scolex is
knob like in shape, has a rostellum with hooklets and four
suckers. The segments are wider than they are long.
 Ova are spherical or ovoid measuring 30-47μm in diameter.
 This is what distinguishes it morphologically from H.
diminuta.
 This membrane has two polar thickenings from which arise
threadlike filaments extending into the space between the
membrane and the colorless hyaline shell, unlike those of H.
diminuta which do not possess any filaments.

47. Hymenolepis nana
Egg of Hymenolepis nana. Hymenolepis nana scolex

48. Hymenolepis nana
Clinical Disease
 Infections due to H. nana may cause no symptoms even with
heavy worm burdens. However, symptoms of restlessness,
irritability, anorexia, abdominal pain and diarrhea have been
reported.
 Heavy worm burdens may be caused by auto-infection which
can be a problem in the immunocompromised.
Laboratory Diagnosis
 Diagnosis is based on recovery and identification of the
characteristic ova in wet mount examination.

49. Hymenolepis diminuta
Introduction
 Hymenolepis diminuta is a small tapeworm commonly found in rats
and mice.
 It has a world wide distribution in these hosts but is infrequently
found in humans.
Morphology
 The ova are large, ovoid and yellowish with a moderately thick
shell. They contain an oncosphere with six hooklets and a clear area
between the oncosphere and the shell.
 They measure 70-85μm by 60-80μm.
 The adult worm is 20–60cm long. It has a scolex with a rostellum
but no hooklets and four suckers (in contrast to H. nana).

50. Hymenolepis diminuta
 The rostellum can be withdrawn into a rostellar sac.
 The tapeworm contains about 1000 proglottids, each of which
is wider than long.
Life cycle and Transmission
 The life cycle of H. diminuta requires an intermediate
arthropod host e.g. earwigs, larval fleas and various beetles.
 Human infection occurs by the accidental ingestion of an
infected arthropod, which contains the cysticercoids.

51. Life cycle

52. Hymenolepis diminuta

53. Hymenolepis diminuta
Clinical Disease
 The symptoms associated with H. diminuta infections are few
if any.
Laboratory Diagnosis
 Diagnosis is based on recovery and identification of the
characteristic ova in wet mount examination as well a formol-
ether concentration of feces. Adult worms and proglottids are
rarely seen in stool samples.

54. Diphyllobothrium latum
Introduction
 Members of this order, commonly known as pseudophyllids,
are chiefly parasites of fish-eating mammals, birds and fish.
 They typically are found with a scolex which is characterized
by two elongated bothria situated with one dorsally and one
ventrally.
 The proglottids are flattened dorsoventrally.
 Diphyllobothrium latum is commonly known as fish
tapeworm.
 It is the largest tapeworm found in man.
 The proglottids are generally wider than they are long.

55. Diphyllobothrium latum
Morphology
 The egg is usually ovoid and has a small knob at the opercular end
and is yellowish-brown in color with a smooth shell, of moderate
thickness.
 They(eggs) measure 58-75μm by 40-50μm in size
 Adult worms can reach up to a length of 10 meters or more and
may contain up to 3,000 proglottids.
 The scolex has no rostellum or hooklets.
 It has two bothria, which are unlike the typical four suckers seen
on the Taenia species.
 The proglottids measure 3μm long and 11μm wide and have a
rosette shaped central uterus.

56. Diphyllobothrium latum
Life Cycle and Transmission
 The life cycle of this tapeworm requires two intermediate hosts.
 The eggs are passed out in human feces, once in water they hatch
out into small ciliates coracidium larvae which swim until
ingested by Copepods.
 It is in these intermediate hosts that growth and development of the
1st larval stage(procercoids).
 When these crustaceans (fresh water) are eaten by fish, the
procercoid larvae continue to develop in the flesh of the fish and
become known as plerocercoid larvae.
 It is this stage of the larvae which develops in man when they eat
undercooked fish and they grow into adult worms in the small
intestine.

57. Life Cycle and Transmission

58. Diphyllobothrium latum
Clinical Disease
 The infection caused by D. latum is due to the ingestion of
raw, poorly cooked fresh water fish.
 The symptoms associated with D. latum infection may be
absent or minimal with eosinophilia.
 There may be occasional intestinal obstruction, diarrhea, and
abdominal pain.
 The most serious symptom is the onset of pernicious anemia.
This is due to a vitamin B12 deficiency, caused by excessive
absorption of the vitamin by the adult worm.

59. Diphyllobothrium latum
Laboratory Diagnosis
 Laboratory diagnosis depends on the recovery of characteristic
eggs from a direct examination of stool sample or from formol
ether concentrate of feces.
 Proglottids may also be seen in fecal samples usually in a
chain of segments from a few centimeters to about half of a
meter in length.

60. The Nematodes
 Infections Acquired Through the Gastrointestinal Tract
 Nematodes (or round worms cylindrical ) are non-segmented
helminths.
 They possess bilateral symmetry and a complete digestive tract with
oral and anal openings; they are tapering/ pointed at both ends.
 They are also found to have separate sexes, with the male being
smaller than the female, ranging in size from a few millimeters to
over a meter in length.
 The Nematode infections have a widespread distribution being
found in both Temperate and Tropical climates.
 They can be found in fresh water, in the sea and the soil,
successfully invading both animals and plants.

61. The Nematodes
 Once hatched in the intestine they undergo an incredible migration.
 The larvae initially burrow into the mucosa, penetrate blood vessels and
appear as second stage larvae in the liver within six hours post-infection.
 Here they remain for several days and develop into third stage larvae, L3.
 These larvae then migrate to the heart and are carried to the lungs via the
pulmonary arteries, arriving within four to seven days.
 From there they break out of the capillaries into the alveoli and finally
work their way up the trachea to the pharynx and reach the small intestine
on the 8th or 10th day post-infection.
 Within the intestine, the larvae begin their third molt and become fourth
stage larvae by the tenth day.
 Two to three months after ingestion of the eggs, the females lay eggs in
the intestine.

62. Ascaris lumbricoides
Morphology
 Ascaris lumbricoides is the largest of the intestinal nematodes
found in man.
 The male measures 15cm with a diameter of 3-4μm and has a
curled tail with protruding spicules.
 The female is 20-35cm long with a diameter of 5μm with a
straight pointed posterior end.
 The ova can be unfertilized, fertilized or decorticated and
can show considerable variation in shape and size.

63. Ascaris lumbricoides
Morphology
 The fertilized ova are easily recognized, oval in shape with a thick
wall showing an irregular bumpy surface.
 They(fertilized forms) measure 45-75μm by 35-50μm.
 The outer covering has an albuminoid coat(mamilated layer),
stained golden brown by bile. Some have lost their albuminoid
wall.
 The unfertilized ova are longer and narrower than the fertile ova,
measuring 75-85μm by 35-50μm.
 The shell layers of the egg provide a very resistant structure which
can withstand many chemicals which make them ideal parasites of
the intestine.

64. Unfertilized (left) and fertilized (right) A.
lumbricoides eggs.

65. Life cycle

66. Ascaris lumbricoides
Clinical Disease
 The patient may have symptoms of pneumonitis with cough and
low grade fever during the migration of the larvae through the liver
and lungs.
 This can be accompanied by wheezing, coughing and eosinophilia.
 In heavy worm burdens the adult worms actively migrate in the
intestine resulting in intestinal blockage, vomiting and abdominal
pain.
 The worms can penetrate through the wall of the intestine, or into
the appendix, travel up the common bile duct, which may become
blocked or they may then enter the gal bladder or liver.
 A heavy worm burden in children may lead to severe nutritional
impairment and retardation in growth.

67. Ascaris lumbricoides
Laboratory Diagnosis
 The adults of A. lumbricoides may be expelled through the anus,
mouth or nose.
Microscopic examination:
 Eggs may be difficult to identify if an excess of iodine is added to
the wet preparation as they retain the stain thus resembling debris.
 The microscopic examination of stool deposits after concentration
reveals the characteristic bile stained ova.
 Ova may also become decorticated.
 In most symptomatic cases identification is easy due to the vast
number of eggs, which can be found within a few seconds of
starting to scan the slide.

68. Hookworm Species
Introduction
 Hookworms infective to man comprise of two species,
Ancylostoma duodenale and Necator americanus
 They are classed as one of the most destructive of human
parasitic helminths.
 There is no intermediate host, with man being the only
definitive host.
 It is estimated that there are some 900 million cases of
infection world wide
 They occur in areas where sanitary and environmental
conditions favor the development of the eggs and larval
infections (e.g., warm, damp soil).

69. Hookworm Species
Introduction
 The geographic distributions of the two species are remarkably
divided into:
1. Necator americanus which predominately is a New World
hookworm, where it was introduced from Africa to the Western
Hemisphere.
o It can also be found in the East, Asia, Africa, South America, and
Oceania.
2. Ancylostoma duodenale is an Old World hookworm; it
is the only species of Europe and areas bordering the
Mediterranean.
o It can also be found in the Middle East, North China, Africa,
Asia, and South America.

70. Hookworm Species
Morphology
 Both species have similar general morphology and measure
approximately, females 10–13μm and males 8–11μm.
 The male species has a posterior copulate bursa which is absent
from the female.
 The females though possess a vulva opening which is found
almost one third of the body length from the posterior end, they
also have two ovaries.
 Most of the female body is occupied with eggs.
 Larvae live for an average of 3–6 weeks in the tropics (A.
duodenale can live at lower temperatures than N. americanus can,
and so is found in more temperate climates).

71. Hookworm Species
Egg of Ankylostoma spp Larvae of ankylostoma spp

72. Hookworm Species
Life Cycle
 The adult worms live in the small intestine, attached firmly to the
mucous membrane of the gut lining, and feed on blood and tissue.
 The adult females deposit their eggs in the gut(they can produce
up to 20,000 eggs per day), the eggs are then passed out in the
feces.
 The rhabditiform first stage larvae(non-infective) hatch in
warm, damp soil, feeding on bacteria.
 After about one week during which they have gone through two
molts become infective(filariform /third stage larvae) and climb
into a suitable position waiting for a suitable host to pass by.

73. Hookworm Species
Life Cycle
 The larvae enter the host by penetrating unbroken skin (it is now
recognized that A. duodenale can successfully enter man by oral
ingestion, this may be more important for this species than skin
penetration).
 The larvae then enter blood vessels and are carried to the heart, lungs and
trachea.
 They are then swallowed and develop into adult worms in the small
intestine.
 The non-infective rhabditiform larvae develop into infective filariform
larvae while passing down the small intestine.
 Autoinfection occurs when the larvae reinfect the host by penetrating the
intestinal mucosa or the perianal or perineal skin.
 The larvae migrate to the lungs via the circulatory system and then return
to the intestine.

74. Life cycle of Ankylostoma species

75. Hookworm Species
Clinical Disease
 Larval penetration of the skin may lead to pruritis, often
termed as ‘ground itch’ at the site of penetration.
 Respiratory symptoms may arise during the larval migration.
 The adult worm in the intestine may cause intestinal necrosis
and blood loss as a result of the attachment of the adult to the
intestinal mucosa.
 Patients with acute infections may experience nausea,
vomiting, abdominal pain, diarrhea and eosinophilia.
 Chronic infections may lead to iron deficiency and anemia
resulting from the excessive loss of iron. Heavy worm burden
in children may have serious consequences including death.

76. Hookworm Species
Laboratory Diagnosis
 Specimen: stool sample, vomitous
 Adults of Hookworm species may be passed out spontaneously
in feces.
 Direct stool examination: to demonstrate characteristic egg of
ankylostoma species( with 7-8 blastomeres)
 The microscopic examination of stool deposits, formol-ether
concentration method concentration reveals the characteristic
ova.

77. Trichuris trichiura
Introduction
 Trichuris trichiura, more commonly known as the Whip Worm,
due to the whip-like form of the body.
 These nematodes are most commonly seen in tropical climates
and in areas where sanitation is poor.
 There are several species within this genus each infecting
specific hosts, but only T. trichiura infects man, Causing
human trichuriasis.
 It is a parasite that infects many more people than is generally
appreciated, up to 800 million people throughout the tropics
and temperate regions.

78. Trichuris trichiura
Morphology
 The thin anterior portion of the worm is found embedded in the mucosa.
 The posterior end is much thicker and lies free in the lumen of the large
intestine.
 The female measures 35-50μm long and the male 30-45μm long.
 Adult worms are found in the cecum and upper part of the colon of man.
 In heavy infection they can be found in the colon and the terminal ileum.
 The ova are characteristically barrel shaped, bile stained with bipolar
plugs.
 They(eggs) measure 50-54μm by 20-23μm.
 Life cycle eggs require a warm, moist environment with plenty of
oxygen to ensure embryonation, but once they have embryonated they
are extremely resistant to environmental conditions.

79. Trichuris trichiura
Life cycle
 Infection is achieved by swallowing soil that contains embryonated eggs.
 Therefore, children are most commonly seen to possess the infections, as
they are more likely to swallow soil.
 When embryonated eggs are swallowed by human hosts larvae are
released into the upper duodenum.
 They then attach themselves to the villi lower down the small intestine or
invade the intestinal walls.
 Within three weeks to a month after infection, during the larvae undergo
four molts to develop to adult warms.
 Once fertilized the female worms lay several thousands of eggs, which
are unsegmented at the oviposition and are passed out in the feces.
 Once they have been passed out they require an embryonation period in
the soil which may last from two weeks to several months, after which
they become infective.

80. Life cycle

81. Trichuris trichiura
Clinical Disease
 In heavy worm burden may result in mechanical damage to the
intestinal mucosa due to the adult worm being threaded into the
epithelium of the cecum.
 Abdominal cramps, tenesmus, dysentery and prolapsed rectum may
occur in these cases.
 If a prolapsed rectum is observed, many worms may be seen
adhering to the mucosa of the rectum.
 Symptomatic infections are usually only seen in children.
 The majority of infections are chronic and mild, with nonspecific
symptoms like diarrhea, anemia, growth retardation, eosinophilia.

82. Trichuris trichiura
Laboratory Diagnosis
 The adult worms of T. trichiura are rarely seen in the feces.
 Direct/ or wet mount examination of stool sample to
demonstrate the characteristic barrel-shaped egg.
 The microscopic examination of stool deposits after an iodine
stained, formol-ether concentration method concentration
reveals the characteristic barrel shaped ova.
 In symptomatic infections numerous numbers of eggs can be
seen due to the prolific nature of the female worms, even in
light infections many eggs can be seen in the smear.

83. Trichuris trichiura

84. Strongyloides stercoralis
Introduction
 Strongyloides stercoralis is an intestinal nematode commonly found
in warm areas, although it is known to survive in the sub-tropics
(hot and humid conditions).
 This parasite is interesting in that it contains a free-living stage
(exogenous) and a parasitic stage (endogenous) where the larvae
undergo development in both stages.
Morphology
 The first stage rhabditiform larvae measure approximately 250μm
long by 20μm wide.
 The third stage or filariform larva is approximately 500μm long .
 Adults are slender and possess and extremely long esophagus which
in the female extends1/3 to1/2 of the body.

85. Strongyloides stercoralis
 Eggs are rarely found in the stool as they hatch in the intestine.
 They are oval and thin shelled, resembling those of hookworm
but are smaller measuring 50-58μm by 30-34μm.
Life cycle
 The life cycle of S. stercoralis is a complex one as
demonstrated in the diagram below.

86. Life cycle of Strongyloides stercoralis

87. Strongyloides stercoralis
Clinical Disease
 Disease associated with infections due to S. stercoralis is varied,
ranging from some patients being totally asymptomatic to the
hyperinfection syndrome.
 There are three areas of involvement in Strongyloides infections;
skin, lungs and intestine.
1. Initial skin penetration of the filariform larvae usually causes
very little reaction.
2. The migration of larvae through the lungs may stimulate an
immune response which can result in a cough, wheezing and fever.
3. Symptoms associated with intestinal strongyloidiasis may mimic
a peptic ulcer due to ulceration of the intestinal mucosa.

88. Strongyloides stercoralis
Laboratory diagnosis
 Specimen: stool sample
 Direct examination/ wet mount examination: microscopic
examination for demonstration of first stage larvae(L1 larvae)
from stool sample

89. Strongyloides stercoralis
Laboratory diagnosis
 Specimen: stool sample
 Direct examination/ wet
mount examination:
microscopic examination for
demonstration of first stage
larvae(L1 larvae) from stool
sample
Larvae of S. stercoralis

90. The Trematodes
Introduction
 The trematodes (or flukes) are leaf shaped.
 There are two suckers or attachment organs, an anterior oral
sucker and a posterior ventral sucker.
 The suckers form a characteristic feature of the group, from which
the name Trematode is derived from the Greek word for “hole.”
 Most trematodes are hermaphrodite and most of the body consists
of reproductive organs and their associated structures.
 The digestive system is well developed; they generally feed on
intestinal debris, blood, mucus and other tissues, depending on the
host environment.

91. The Trematodes
 Trematodes require an intermediate host in their life cycle with
vertebrates being the definitive host.
 Larval stages may occur in either invertebrate or vertebrate hosts.
 Most Trematodes inhabit the alimentary canal of vertebrates and
many of the associated organs, such as the liver, bile duct, gall
bladder, lungs, bladder and ureter.
 These organs are rich in cavities containing food such as blood,
mucus, bile and intestinal debris.
 There may be five common larval stages – the miracidium,
sporocyst, redia, cercaria, and the metacercaria
 Trematode eggs have a smooth hard shell and the majority of them
are operculate.

92. Schistosomes
Introduction
 The Schistosomes are blood trematodes.
 They differ from other trematodes in that they have separate
sexes.
 They require definitive and intermediate hosts to complete
their life cycle.
 There are three most common species of Schistosomes
responsible for human disease; S. mansoni, S. haematobium
and S. japonicum.
 Over 200 million people are infected in over at least 75
countries with 500 million or more people exposed to
infection.

93. Schistosomes
Introduction
 With the disease spreading due to improved water supplies being
created therefore, forming potentially new habits for snails.
 The disease caused is called schistosomiasis or Bilharzia and is the
most important of helminth diseases.
 Infection by the three most common species is the same in both
sexes and in all age groups.
 Though, S. mansoni and S. haematobium is seen to occur more
often and most heavily in teenagers especially males.
.

94. Schistosoma mansoni
Introduction
 The intermediate host is an aquatic snail, Man is the most common
definitive host.
 The adult worms live in smaller branches of the inferior mesenteric
vein in the lower colon.
Morphology
 The adult males measure up to 15 millimeters in length and females
up to 10μm.
 The ova of S. mansoni are 114-175μm long by 45-68μm wide.
 They are light yellowish brown, elongate and possess a lateral
spine.

95. Schistosoma mansoni
Egg of S. mansoni
 S. mansoni ova, clearly
showing its lateral spine
which is a good
distinguishing factor when
identifying Schistosome ova.
 They range in size between
114-175μm long by 45-
68μm wide.
Egg of S.mansoni

96. Schistosoma mansoni
Clinical Disease
 The clinical disease is related to the stage of infection, previous
host exposure, worm burden and host response.
 Cercarial dermatitis (swimmers itch) follows skin penetration and
results in a maculopapular rash which may last 36 hours or more.
 Their eggs are laid and they penetrate the intestinal wall. They are
then excreted in the feces, often accompanied by blood and mucus.
 It is the eggs and not the adult worms, which are responsible for
the pathology associated with S. mansoni infections.
 The adult flukes acquire host antigen which protects them from the
host's immune response.

97. Schistosoma mansoni
Clinical Disease
 The host's reaction to the eggs which are lodged in the intestinal
mucosa, leads to the formation of granulomata and ulceration of
the intestinal wall.
 The granulomatous response to these eggs can result in the
enlargement of the liver with fibrosis.
 The spleen may also become enlarged. Other complications may
arise as a result of deposition of the eggs in other organs e.g.
lungs.
 Katayama fever is associated with heavy primary infection and
egg production.
 Hepatosplenomegaly, lymphadenopathy, eosinohilia and
dysentery.

98. Schistosoma mansoni
Laboratory Diagnosis
Specimen:
Stool sample, biopsy
Microscopy
 Laboratory confirmation of S. mansoni infection can be made
by finding the eggs in the feces in direct/ wet mount stool
examination/ after an iodine stained,
 Formol-ether concentration method.
 When eggs cannot be found in the feces, a rectal biopsy can be
examined.

99. Schistosoma haematobium
Introduction
 Schistosoma haematobium is the causative agent of urinary
schistosomiasis.
 It occurs in Africa, India and the Middle East.
 The intermediate host is the Bulinus snail.
 The females deposit their eggs in the walls of the bladder and finally
making their way into the urine.
 The life cycle is very similar to that of S. mansoni.
Morphology
 The adult worms are longer than those of S. mansoni. The ova are
relatively large, measuring 110-170μm in length and 40-70μm in width.
 They have an elongated ellipsoid shape with a prominent terminal spine.

100. Schistosoma haematobium
Egg of S. haematobium
 Schistosoma haematobium
eggs are elongated with a
prominent terminal spine.
The
 Larva inside the egg
produces an enzyme that
passes through the egg-
shell.
Egg of S haematobium

101. Schistosoma haematobium
Clinical Disease
 Cercarial dermatitis (Swimmer’s Itch) following skin penetration.
 The mature flukes of S. haematobium migrate to the veins surrounding the
bladder.
 After mating, the eggs are laid in the venules of the bladder and many penetrate
through the mucosa, enter the lumen of the bladder and are excreted in the urine
accompanied by blood.
 Thus hematuria and proteinuria are characteristic, though not invariable features
of urinary schistosomiasis.
 As with all Schistosoma species, it is the eggs and not the adult worms which are
responsible for the pathology associated with S. haematobium. In chronic
disease, eggs become trapped in the bladder wall resulting in the formation of
granulomata.
 Following prolonged infection, the ureters may become obstructed and the
bladder becomes thickened resulting in abnormal bladder function, urinary
infection and kidney damage

102. Schistosoma haematobium
Laboratory Diagnosis
 The definitive diagnosis of urinary schistosomiasis is made by finding the
characteristic ova of S. haematobium in urine.
 Terminal urine should be collected as the terminal drops contain a large
proportion of the eggs.
 The urine can either be centrifuged and the deposit examined
microscopically for ova.
 A bladder biopsy is seldom necessary to make the diagnosis.
 There is a marked periodicity associated with the time when most eggs
are passed out.
 Higher numbers of eggs are encountered in urine specimens passed
between 1000 and 1400 hours, presumably as a result of changes in the
host’s metabolic and physical activities.

103. NUB1106: Microbiology and
Parasitology
Unit4: Mycology

104. Mycology
1. DEFINITION:
 Fungi are eukaryotic, with filamentous structures, and produce
spores forming organisms.
 These organisms grow as saprophytes and decompose dead organic
matter.
2. MORPHOLOGY
 Microscopic fungi exist in two basic morphological types:
1. Hyphae: are long threadlike cells that make up the bodies of
filamentous fungi, or molds. The intertwining mass of hyphae that
makes up the body or colony of a mold is called a Mycelium.
 Vegetative hyphae are responsible for the production of fungal
reproductive bodies called spores.

105. Mycology
2. A yeast: this form is distinguished by its round to oval shape and
by its mode of asexual reproduction.
 Some fungi occur in both the yeast and mycelial forms. These are
called dimorphic fungi.
 Dimorphic fungi : The dimorphic fungi have two forms:
 YEAST - (parasitic or pathogenic form). This is the form usually
seen in tissue, in exudates, or if cultured in an incubator at 37
degrees C.
 MYCELIUM - (saprophytic form). The form observed in nature
or when cultured at 25 degrees C. Conversion to the yeast form
appears to be essential for pathogenicity. Dimorphic fungi are
identified by several morphological or biochemical characteristics.

106. Mycology
3. FUNGAL NUTRITION
 All fungi are heterotrophic. Most fungi are saprobes, meaning that
they obtain these substrates from the remnants of dead plants and
animals in soil or aquatic habitats. Fungi can also be parasites on
the bodies of living animals or plants.
4. REPRODUCTIVE STRATEGIES AND SPORE
FORMATION
 The most general subdivision is based on the way the spores arise.
 Asexual spores are the products of mitotic division of a single
parent cell, and sexual spores are formed through a process
involving the fusing of two parental nuclei followed by meiosis.

107. Mycology
A. Asexual spore formation:
There are two subtypes of asexual spore:
 Sporangiospores are formed by successive cleavages within a
saclike head called a sporangium which is attached to a stalk, the
sporangiosphore. Spores released when the sporangium ruptures.
 Conidia (conidiospores) are spores not enclosed by a spore-bearing
sac. The develop either by the pinching off of the tip of a special
fertile hypha or by the segmentation of a pre-existing vegetative
hyphae.

108. Mycology
 Sexual spore formation
The majority of fungi produce sexual spores at some point. The nature of
this process varies from the simple fusion of fertile hyphae of two different
strains to a complex union of differentiated male and female structures.
5. ROLES OF FUNGI
 Fungal cell walls give off chemical substances that can cause allergies
 The toxins produced by poisonous mushrooms can induce neurological
disturbances and even death.
 The mold Aspergillus flavus synthesizes a potentially lethal poison called
aflatoxin, which is the cause of a disease in domestic animals that have
eaten grain contaminated with the mold and is also a cause of liver
cancer in humans.

109. Mycology
5. ROLES OF FUNGI
 Beneficial side, however, fungi play an essential role in decomposing
organic matter and returning essential minerals to the soil.
 Fungi produce large quantities of antibiotics, alcohol, organic acids, and
vitamins.
 Yeast saccharomyces produces the alcohol in beer and wine and the gas that
causes bread to rise.
 Blue cheese, soy sauce, and cured meats derive their unique flavours from
the actions of fungi.
6. CLINICAL CLASSIFICATION OF THE MYCOSES
 True pathogens:
– Superficial mycoses
– Cutaneous mycoses
– Subcutaneous mycoses
– Systemic mycoses

110. Mycology
Opportunistic mycoses
1. Superficial mycoses
 Agents of mycoses involve the outer epidermal surface .
 Tinea versicolore (pityriasis versicolor): is caused by the yeast
Malassezia furfur, a normal inhabitant of human skin that feeds on the
high oil content of the skin glands.
 The disease is a condition characterized by a rash on the trunk and
proximal extremities, are transmitted to man by direct exposure.
 Piedras: are marked by colored concretion forming on the outside surface
of hair shafts. In white piedras, caused by Trichosporon beigelii, a white
to yellow adherent mass develops on the shafts of scalp, pubic, or axillary
hair. Black piedras, caused by piedraia hortae, is characterized by dark-
brown nodules, mainly on scalp hairs.

111. Mycology
2. Cutaneous mycoses
 The cutaneous mycoses are usually confined to the outer layers of
skin (stratum corneum), hair, and nails, and do not invade living
tissues. The fungi are called dermatophytes.
 Dermatophytes, or more properly, keratinophilic fungi, produce
extracellular enzymes (keratinases) which are capable of
hydrolyzing keratin. Diseases are termed dermatophytoses.
Common terms used in reference to these diseases are ringworm,
because they tend to develop in circular, scaly patches, and Tinea. .
 Epidemiology: The natural reservoirs of dermatophytes are other
humans, animals, and the soil. Dermatophytic fungi exist
throughout the word.

112. Mycology
Etiologic Agents: There are three genera of dermatophytes:
1. Trichophyton species
 These infect skin, hair and nails.
 Trichophyton rubrum is presently the most common cause of tinea.
2. Microsporum species
 These may infect skin and hair, rarely nails.
 Microsporum canis is one of the most common dermatophyte
species infecting humans.
3. Epidermophyton floccosum
 These infect skin and nails and rarely hair.

113. Mycology
Clinical Manifestations
1. Tinea capitis (Ringworms of the Scalp): this mycosis results from
the fungal invasion of the scalp and the hair of the head, eyebrows, and
eyelashes.
 Very common in children and adults .
 Manifestations range from small, scaly patches (Gray patch), to a
severe inflammatory reaction (kerion), to destruction of the hair
follicle and permanent hair loose.
2. Tinea barbae (Ringworm of the Beard): This tinea, affect the chin
and beard of adult males.
3. Tinea corporis (Ringworm of the body can appear nearly
anywhere on the body, and it is transmitted primarily by direct contact
and fomites (clothing, bedding).

114. Mycology
Clinical Manifestations
 The infection usually appears as one or more scaly reddish rings on
the trunk, hip, arm, neck, or face.
4. Tinea cruris (Ringworm of the groin): sometimes known as jock
occurs mainly in males on the groin, perianal skin, scrotum, and
occasionally, the penis.
 The fungus thrives under conditions of moisture and humidity
created by profuse sweating or tropical climates.
 It is transmitted primarily from human to human.
5. Tinea pedis (Ringworm of the foot): known by a variety of
synonyms, including athlete’s foot and jungle rot. Infections begin
with small blisters between the toes that burst, and can spread to the
rest of the foot and nails.

115. Mycology
Clinical Manifestations
6. Tinea manuum (Ringworm of the hand): infection of the hand
by dermatophytes is nearly always associated with concurrent
infection of the foot. Lesions usually occur on the fingers and palms
of one hand, and they vary from white and patchy to deep and
fissured.
7. Tinea unguium (Ringworm of the nail): Finger nail and toe nails,
being masses of keratin, are often sites for persistent fungus
colonization. The first symptoms are usually superficial white patches
in the nail bed. A more invasive form causes thickening, distortion,
and darkening of the nail. Nail problems caused by dermatophytes are
on the rise as more women wear artificial fingernails, which can
provide a portal of entry into the nail bed.

116. Mycology
7. Diagnosis of Ringworm
 In most cases, direct microscopic examination and culturing are
needed.
 Diagnosis of tinea of the scalp caused by some species of
Microsporum is aided by use of a long-wave ultraviolet lamp that
causes infected hairs to fluoresce.
 Samples of hair, skin scrapings, and nail debris treated with
heated KOH show a thin, branching fungal mycelium if infection
is present.
 Culturing specimens on selective media (SDA: Sabouraud
dextrose agar)

117. Mycology
8. Treatment of Dermatophytoses
 The most satisfactory choise for therapy is a topical antifungal
agent. Ointments contening miconazole, or even menthol and
camphor (vicks) are applied regularly for several weeks.
 Some drugs work by speeding up loss of outer skin layer.
Intractable infections can be treated with Lamisil or Griseofulvin.
 However placing a patient on these relatively toxic drugs for up to
1 to 2 years is probably too risky in most cases.
 Gentle debridement of skin and ultraviolet light treatments can
have some benefit.

118. Mycology
3. Subcutaneous Mycoses
 When certain fungi are transferred from soil or plants directly into
traumatized skin, they can invade the damaged site.
 Such infections are termed subcutaneous because they involve
tissues within and just below the skin.
 Most species in this group are greatly inhibited by the higher
temperatures of the blood and viscera, and rarely do they
disseminate.
a) Sporotrichosis (Rose-Gardener’s Disease)
 The cause of Sporotrichosis, sporothrix schenckii, Sporothrix
resides in warm, temperate, and moist areas of the tropics.

119. Mycology
4. Systemic mycosis: Histoplasmosis (Histoplasma capsulatum)
 Histoplasmosis is a systemic disease, mostly of the
reticuloendothelial system, manifesting itself in the bone marrow,
lungs, liver, and the spleen.
 The ecological niche of H. capsulatum is in blackbird roosts,
chicken houses and bat.
 Patients who develop histoplasmosis (95%) are asymptomatic. In
the patients who are clinically ill, histoplasmosis generally occurs
in one of three forms: acute pulmonary, chronic pulmonary or
disseminated.
 The diagnosis is made from their history, serologic testing or skin
test. In peripheral blood, H. capsulatum appears as a small yeast
about 5-6 microns in diameter.

120. Mycology
 Gastric washings are also a source of H. capsulatum as people with
pulmonary disease produce sputum and frequently swallow their
sputum.
 Treatment: The drug of choice is amphotericin B, with all its side
effects. Itraconazole is now also being used for mild cases.
5. Opportunistic mycoses
 The yeast Candida is the dominant opportunistic pathogen, and it
accounts for the majority of invasive infections.
 The mold Aspergillus is the second in incidence, accounting for
the most lung infections.
 Other fungi that are appearing more often in clinical isolates are
Cryptococcus neoformans(cryptococcal meningitis).

121. Mycology
a) Infections by candida : candidiasis
Candida albicans, extremely widespread yeast, is the major cause of candidiasis (also
called candidosis or moniliasis).
Epidemiology of Candidiasis
 Candida albicans occurs as normal flora in the oral cavity, genitalia, large
intestine, or skin of 20% of humans.
 The risk of invasion increases with extreme youth, pregnancy, drug therapy,
immunodeficiency, and trauma.
 Candida albicans cause local infections of the mouth, pharynx, vagina, skin,
alimentary canal, and lungs, and it can also disseminate to internal organs. The
mucous membranes most frequently involved are the oral cavity and vagina.
 Thrush: is a white patchy infection affecting the membranes of the oral cavity or
throat, usually in newborn infants and elderly, debilitated patients.

122. Mycology
 Vulvovaginal candidiasis: Known more commonly as yeast
infection, has widespread occurrence in adult women, especially
those who are taking oral antibiotics or those who are diabetic or
pregnant, all condition that can disrupt the normal vagina flora.
Candidal vaginitis also poses a risk for neonates, who can be
infected during childbirth.
 Onychomycosis: is the candidal that attack keratinized structures
such as skin and nails.
 Intertriginous: infection occurs in moist areas of the body where
skin rubs against skin, as beneath the breasts, in the armpit, and
between folds of the groin.

123. Mycology
 Cutaneous candidiasis can also complicate burns and produce a
scaldlike rash on the skin of neonates
 Candidal bood infection usually becomes systemic in patients chronically
weakened by surgery, bone marrow transplants, advanced cancer.
 The presence of C. albicans in the blood is such a serious assault that it
causes more human mortalities than any other fungal pathogen. Principal
targets of systemic infections are the urinary tract, endocardium, and
brain.
Diagnosis of candidiasis
The clinical material to be sent to the lab depends on the presentation of the
disease: blood, vaginal discharge, urine, feces, nail clippings or material
from cutaneous or mucocutaneous lesions. A presumptive diagnosis of
Candida infection is made if budding yeast cells and pseudohyphae are found
in the specimens from localized infections. The species are identified by
biochemical reactions if cultured.

124. Mycology
Treatment of Candidiasis
 The drugs of choice for systemic infection are amphotericin B and
fluconazole.
 Superficial mucocutaneous infection consists of topical antifungal
agents. Terbinafine has been approved for treating onychomycosis.
b) Cryptococcosis and Cryptococcus neoformans
Cryptococcus neoformans is the widespread resident of human
habitats. This yeast has a spherical to ovoid shape, with small,
constricted buds and a large capsule that is important in it
pathogenesis.

125. Mycology
Exams and Tests:
1. Sputum culture and stain
2. Lung biopsy
3. Bronchoscopy ,
4. Cerebrospinal fluid culture
5. Stain for Cryptococcus and Chest x-ray
6. Cryptococcal antigen test.
Medications include:
 Amphotericin B
 Fluconazole

126.  Mycology
Aspergillosis
 Aspergillus is a fungus whose spores are present in the air we breathe,
soil, food, air vents but does not normally cause illness. However an
individual with a weakened immune status may be susceptible to
aspergillus infection.
 The most common etiologic agents of aspergillosis are: Aspergillus
fumigatus and Aspergillus flavus, aspergillus niger
 They may cause endocarditis, osteomyelitis, otomycosis and cutaneous
lesions.
 The patients may cough up the fungus elements because the organism
frequently invades the bronchus.
 Combined therapy of Amphotericin B and other antifungal agents
(Voriconazole) is the only effective treatment for systemic disease.

127. NUB1106: Microbiology and
Parasitology
A. CLINICAL VIROLOGY

128. INTRODUCTION
A. General Characteristics of Viruses
1. Viruses do not fall strictly into the category of unicellular
microorganisms as they do not possess a cellular organisation.
2. Viruses are obligate intracellular parasites unable to self-replicate.
Once inside living cells.
3. They lack enzymes necessary for protein and nucleic acid synthesis and
are dependent for replication on the synthetic machinery of host cells
4. They multiply by a complex process and not by binary fission
5. They are unaffected by antibiotics.
6. The genome is either DNA or RNA (single or double stranded).
7. Viruses do not have a system to produce ATP.
8. Range in size from100 to 400 nm.
9. The classification of viruses is based on nucleic acid type, size and shape
of virion, and presence or absence of an envelope.

129. Definitions
 Virion is the entire viral particle.
 Capsid is the protein coat that encloses the genetic material.
 In some viruses, special capsid proteins called spikes help attach
the virus to the host cell and facilitate penetration of the cell.
 Capsomer is the protein subunit that makes up the capsid.
 Nucleocapsid is composed of the capsid and genetic material.
 The envelope is the outer coating composed of a phospholipid
bilayer, which is composed of viral-encoded glycoproteins.
 The envelope is derived from a host cell's membrane.

130. steps for viral replication
1. Adsorption is attachment of the virus to a specific receptor on the host cell.
2. Pentration is entry of the virus into the host cell. Penetration. Following
attachment, the tail of the phage releases lysozyme, an enzyme that dissolves a
portion of the cell
3. Uncoating occurs when there is either the separation of the capsid from the
genome or rearrangement of the capsid proteins exposing the genome for
transcription and replication.
4. Biosynthesis, Having entered the cytoplasm, production of new phage
genomes and capsid parts begins.
a. Viral DNA or RNA serves as the template for mRNA production.
b. mRNA codes for viral protein and enzymes necessary for nucleic acid synthesis.

131. MODE OF VIRAL MULTIPLICATION
 Adsorption: the virus attaches to its host cell by specific binding of its spikes to
cell receptors.
 Penetration: the virus is engulfed into a vesicle by endocytosis.
 Uncoating: the envelope of the virus is removed, and the DNA
 Synthesis: replication and protein production: RNA molecules, capsomers, spikes
 Assembly: viral spike proteins are inserted into the cell membrane for the viral
envelope; nucleocapsid is formed from RNA and capsomers.
 Release: Enveloped viruses bud off of the membrane, carrying away an envelope
with the spikes.
 a. Cell lysis: Naked viruses lyse host cell and leave through a hole in the
plasma membrane.
b. Budding: Intact virion pushes outward from a host's membrane. The mne
wraps around the virion; the membrane is cleaved and then resealed around the
virion, thus becoming the viral envelope.

132. Viral penetration to host cell

133. Viral budding(released from infected
host cell)

134. Interaction between viruses and infected cells.
 At cellular level, viral infection may cause effects ranging from no apparent
cellular damage to rapid cell destruction:
 Some viruses like the poliovirus, cause cell death(cytocidal effect) or even
lysis(cytolysis).
 Other cause cellular proliferation or malignant transformation (oncogenic
viruses).
 In tissue culture, viral infection may lead to readily observable cellular
changes(cytopathic effects)
 A large amount of viral macromolecules that accumulate in the infected cell may
distort the cellular architecture and exert a toxic effect.
 The permeability of plasma membrane may be altered, releasing the lysosomal
enzyme and leading to autolysis.
 Respiratory syncytial virus(RSV) cause fusion of adjacent cell membaranes
leading to polykaryocytosis or syncytium formation.

135. Interaction between viruses and infected cells.
 Virus coded antigens may appear on the surface of infected cells, this
confer new properties on the cells.example viral hemagglutin appears on
the surface of cells infected with the infuenza virus and cause adsorption
of erythrocytes to the cell surface(hemadsorption)
 Certain viruses such as measles, mumps, adenoviruses,
cytomegaloviruses and varicella virus cause damage to the chromosome
of host cell.
 The most characteristic histological feature in virus infected cell is the
appearance of inclusion bodies.
 The inclusion bodies may be present with cytoplasm(poxviruses),
nucleus(herpesviruses) or both( measles viruses)
 The presence of intracytoplasmic eosinophilic inclusion (negri bodies) in
the brain cells of animal justifies the presumptive diagnosis of rabies.

136. Mode of transmission
1. The respiratory tract offers the most important portal of entry of
viruses. Smallpox and chickenpox, influenza and rhinovirus are
examples of such systemic disease in which the portal of entry is the
respiratory tract.
2. The alimentary tract is the next most important route of entry for
viruses, ex. Hepatitis A virus, hepatitis E virus.
3. Skin, of the viruses that enter through the skin, only few produce a local
lesions, viruses enter the skin through abrasions(papillomavirus).
4. Insect bites(arboviruses)
5. Animal bites(rabies virus)
6. The conjunctiva also may act as a portal of entry for viruses, this may
lead to local disease(adenovirus) or to systemic spread( measles).
7. Genital tract (sexual contact), ex. HIV, Herpes simplex virus-2(HSV-
2).
8. Congenital infection ex. Rubella and cytomegalovirus and HSV-2
produce maldevelopment or severe neonatal disease.

137. Specimen Processing for Diagnosis of Viral
Diseases
1. Samples should generally come from the infected site.
a. Skin infections: Rash site
b. Blood (serum/plasma, stool, urine
b. Respiratory infections: Sputum or throat swabs
c. Central nervous system: For diagnosis of meningitis, cerebrospinal fluid (CSF)
and serum, as well as stool or throat swabs for polio,
d. Urogenital infections: Needle aspirates and endocervical and urethral swabs
e. Gastrointestinal tract: Stool samples and rectal swabs
f. Eye infections: Eye swabs and corneal scrapings
g. Throat, nasal swab, ex. Corona virus

138. Viral infections of the respiratory tract
Viral Infections of the Upper Respiratory Tract(Nose, pharynx,
middle ear and auditory tubes)
 The common cold is the most common viral infections of
the URT.
1. Rhinoviruses (rhino “nose”) are a broad group of over 100
different naked, viruses.
 They belong to the family Picornaviridae (pico “small)
 They are transmitted through airborne droplets or by contact with
an infected person or contaminated objects.
2. Adenoviruses (family Adenoviridae) are a group of over 50 types
of non-enveloped.

139. Viral Infections of the Lower Respiratory Tract
 The lower respiratory tract (LRT) in humans consists of the larynx,
trachea, bronchial tubes, and the alveoli.
 1. Influenza viruses are involved with seasonal (winter) epidemics and
occasional pandemics.
 Influenza (the “flu”) is a highly contagious acute disease that is
transmitted by airborne respiratory droplets.
 The enveloped influenza virion belongs to the Orthomyxoviridae family.
 Projecting through the envelope are two types of spikes.
 One type contains the enzyme hemagglutinin (H), a substance
facilitating the attachment and penetration of influenza viruses into
host cells.
 The second type contains another enzyme, neuraminidase (N), a
protein assisting in the release of the virions from the host cell when
replication is complete.

140. Viral Infections of the Lower Respiratory
Tract
 Influenza A strikes every year and causes most “flu” epidemics.
 It circulates in many animals,including birds, pigs, and humans.
 Type A is divided into subtypes based on the H and N surface
glycoproteins.
 Influenza B also strikes every year but is less widespread than
type A.
 It only circulates between humans and is not divided into subtypes.
 Influenza C causes a mild respiratory illness but not epidemics.

141. Viral Infections of the Lower Respiratory
Tract
2. Paramyxovirus
 The paramyxoviruses are a group of viruses causing similar
symptoms.
 A number of viruses, primarily in the Paramyxoviridae, are
associated with the LRT, all these viruses are enveloped.
3. Respiratory syncytial (RSv) disease is caused by the respiratory
syncytial virus (RSV). RSV is transmitted by respiratory droplets
or virus-contaminated hands.
4. The SARS(severe acute respiratory syndrome) coronavirus and
hantaviruses cause unique forms of pneumonia.

142. Viral Infections of the GIT
 These illnesses include hepatitis and viral gastroenteritis.
 Hepatitis Viruses A and E areTransmitted through oral route
1. Hepatitis A and E are spread by the fecal-oral route.
 Hepatitis A is an acute inflammatory disease of the liver most
commonly transmitted by food or water contaminated by the feces
of an infected individual.
 Hepatitis A is caused by a small, naked virus belonging to the
Picornaviridae family.
 Hepatitis E is an opportunistic, emergent disease caused by a
naked virus of the Caliciviridae family.

143. Viral Infections of the GIT
2. Rotavirus infections represent one of the world’s deadliest
forms of gastroenteritis in children.
 The rotavirus is a naked, circular-shaped virus.
 It is a member of the Reoviridae family.
 Rotavirus infections tend to occur in the cooler months “winter
diarrhea.”
 Transmission occurs by ingestion of contaminated food or water
(fecal-oral route), or from contaminated surfaces.

144. Viral Diseases of the Nervous System
 Rabies, polio, and West Nile fever are perhaps the most
recognized diseases.
 The Rabies Virus is of Great Medical Importance Worldwide
 Rabies is a highly fatal disease once symptoms arise.
 Rabies (rabies = “madness”) is notable for having the highest
mortality rate of any human disease,
 There are an estimated 55,000 deaths annually, mostly in rural
areas of Africa and Asia.The rabies virus is a virion of the
Rhabdoviridae family

145. Viral Diseases of the Nervous System
 Animal rabies can occur in most warm blooded animals, including
dogs, cats, and bats.
The Polio Virus
 The name polio is a shortened form of poliomyelitis (polio
)referring to the “gray matter,” which is the nerve tissue of the
spinal cord and brain in which the virus infects.
 The polioviruses, being in the Picornaviridae family, are among
the smallest virions, measuring 27 nm in diameter.
 Polioviruses usually enter the body by contaminated water and
food.
 They multiply first in the tonsils and then in lymphoid tissues of
the gastrointestinal tract, causing nausea, vomiting, and cramps.

146. Viral Diseases of the Nervous System
 In the most severe cases, the viruses infect the medulla of the brain,
Nerves serving the upper body torso are affected. Swallowing is
difficult,and paralysis develops in the tongue, facial muscles, and
neck. Paralysis of the diaphragm muscle causes labored breathing
and may lead to death.
Arbovirus: Viruses that are transmitted by mosquitoes and ticks
(arboviruses; arbo = arthropod-borne).
 Arboviral encephalitis is an example of a zoonosis, a disease
transmitted by a vector from another vertebrate host to humans.
 Mosquitoes are the most common vector
 West Nile virus disease it is caused by the West Nile virus
(WNV), another member of the Flaviviridae

147. Varicella-Zoster Virus
 90% of pregnant women already immune, therefore primary
infection is rare during pregnancy
 Primary infection during pregnancy carries a greater risk of
severe disease, in particular pneumoniaVZV can cross the placenta
in the late stages of pregnancy to infect the fetus congenitally.
 If rash in mother occurs more than 1 week before delivery, then
sufficient immunity would have been transferred to the fetus.
 Zoster immunoglobulin should be given to susceptible pregnant
women who had contact with suspected cases of varicella.

148. FAMILIES OF RNA VIRUSES
Family Important human viruses
Picornaviridae Rhinovirus, poliovirus, enterovirus, ECHO virus,
coxsackievirus, hepatitis A virus
Orthomyxoviridae Influenza A, B, and C viruses
Coronaviridae Coronavirus
Rhabdoviridae Rabies virus
Filoviridae Marburg and Ebola viruses
Bunyaviridae California encephalitis, Crimean-Congo viruses

149. FAMILIES OF RNA VIRUSES
Family Important human viruses
Retroviridae Human T lymphotropic and human immunodeficiency viruses
Reoviridae Rotavirus and reovirus
Paramyxoviridae Measles, mumps, respiratory syncytial, parainfluenza, and
metapneumo viruses
Togaviridae Rubella virus and western, eastern, and Venezuelan equine
encephalitis
viruses
Flaviviridae Yellow fever, dengue, St. Louis encephalitis, hepatitis C, and
West
viruses

150. Picornaviruses
Poliovirus
 Poliovirus is transmitted by the fecal-oral route. The virus
initially infects the gastrointestinal tract but spreads to the CNS.
Polio vaccines:
 The Salk vaccine is a formalin-inactivated vaccine.
 The Sabin vaccine is an attenuated vaccine.
 The Sabin vaccine produces a stronger immune response.
However, because the attenuated virus can sometimes produce
severe infection, most countries now routinely use the Salk
vaccine.

151. Polioviruses
Morphology of poliovirus
 The virion is spherical
particle, about 27 nm in
diameter, the genome is single
strand of positive sense RNA.
 This genome RNA serves as a
mRNA and initiates the
synthesis of virus
macromolecules.

152. Laboratory diagnosis and prevention
Laboratory diagnosis:
 Specimens: blood, CSF, throat swab, and faeces.
 The virus can be isolated from throat in the early stages of the disease.
 Virus isolation in faeces is possible in 80% of patients in the first week, 50% till
third week of infection.
Prevention:
 Salk’s killed polio vaccine or injectable poliovaccine(IPV)
 Live polio vaccine is administered orally and is therefore known as the oral
polio vaccine(OPV).
 Oral vaccine is not safe in immunodeficient or immunosuppressed individuals.
OPV is obviously preferable to killed vaccine given by injection, however killed
vaccine has an advantage as it can be administered along with DPT vaccine as
quadruple vaccine.
 Killed vaccine induces only systemic antibody response, there is no intestinal
immunity.
 Live vaccine on the other hand, also induces local immunity and systemic
immunity.

153. Arboviruses
 Arboviruses are also called arthropod-borne viruses, these viruses
of vertebrates biologically transmitted by hematophagous insect
vectors.
 They multiply in blood sucking insects and are transmitted by bites
to vertebrates hosts.
 Arboviruses are worldwide in distribution but are more common in
tropical than in temperate zones.
 Arboviruses have been placed in Toga-, Flavi-, Bunya-, reo- and
Rhabdovirus families.
 The ability to multiply in arthropods is their special characteristic.
 The most important arbovirus vectors are mosquitoes , followed by
ticks.

154. Taxonomy of important arboviruses
Family Genus Importany species
Togaviridae Alphavirus Chikungunya
Flaviviridae Flavivirus Yellow fever,dengue
types1-4, West nile virus
Bunyaviridae Bunyavirus California encephalitis
Phlebovirus Rift valley fever virus,
Sandfly fever viruses.
Reoviridae Orbivirus Colorado tick fever

155. Bunyaviridae
 Bunyaviridae family contains over 300 species, it is the largest group of
arboviruses.
 The virus is about 100 nm in diameter and has a complex structure with a
triple segmented genome of single stranded RNA.
 Most bunyaviruses are mosquito-borne viruses, some are transmitted by
sandflies, example Phlebotomus fever, or ticks( Cremean Congo
hemorrhagic fever)
 Bunyaviruses are so named from the type species Bunyamwera virus
isolated from mosquitoes in Uganda, in 1946.
 The family Bunyaviridae contains four genera of medical importance:
Bunyavirus, Phlebovirus, Nairovirus and Hantavirus.
 The clinical disease caused is encephalitis, aseptic meningitis and fever.
 The virus is transmitted by culicoides.

156. Genus Phlebovirus
 The major members of this genus are the sandfly fever and rift
valley fever viruses.
 Phlebovirus fever also known as Pappataci fever and three day
fever, is a self limited fever transmitted by bites of the sandfly
Phlebotomus papatasii.
 It is commonly seen along with Mediterranean and central
Asia.
 Rift valley fever is a mosquito-borne virus
 Human infection causes a disease resembling influenza.

157. Flaviviruses
 The family Flaviviridae contains only one genus, Flavivirus
 They measure 40nm in diameter, the name Flavivirus refers to
the type species, the yellow fever virus.
 They are grouped into two groups:
1. mosquito-borne viruses
2. Tick-borne viruses
Mosquito-borne group: Encephalitis viruses, St Louis
encephalitis virus, it is prevalent in North and Central America
is the most important mosquito-borne disease.

158. Flaviviruses
 West Nile virus, isolated first in West Nile in Uganda, it has
been reported in many African countries.
 It cause a dengue like illness in humans, it is endemic in
Egypt, affecting mainly children.
 Like St Louis encephalitis virus, West Nile virus is also
transmitted by culex mosquitoes.
 It causes a mosquito-borne epidemic of fever, encephalitis and
muscle weakness.
 Murray Valley encephalitis virus, it is seen in Australia.
 The virus was isolated during an epidemic of encephalitis in
the murray valley
 The culex mosquito is the vector

159. Flaviviruses
 Japanese encephalitis, it is commonly seen in Korea and Japan
 The virus was isolated first in Japan, it is commonly found in
temperate regions than tropics region
 It is transmitted by culex mosquito, particularly those which
breeds in rice fields.
 Japanese encephalitis is the most serious among the five
viruses
 The disease is characterised by symptoms such fever,
headache and vomiting, then signs of encephalitis occur after1-
6 days, and signs of encephalitis, convulsions and coma may
follow.

160. Yellow fever
 The most serious epidemics occurred in the West hemisphere, Central
America, Africa and South America.
 After an incubation period of 3-6 days, the disease starts as a fever of
acute onset with chills, headache, nausea and vomiting.
 Jaundice, albuminuria and hemorrhagic manifestation develop and the
patient may die of hepatic and renal failure.
 The virus is transmitted by the domestic Aedes aegyptii mosquito.
 The control of urban yellow fever can be achieved by eradicating the
vectors mosquitoes.
 The vaccine is administered by subcutaneous inoculation

161. Dengue virus , Chikungunya virus
 Dengue virus is widely distributed throughout tropics and subtropics.
 Four types of dengue fever exist DEN1-4
 Lymphadenopathy and maculopapular rash.
 Incubation period 3-14 days, as fever of sudden onset with headache, pain
in the back and limbs,
 Dengue virus is transmitted from person to person by Aedes aegyptii
mosquitoes.
 Chikungunya virus, the virus was first isolated from humans and Aedes
aegypti mosquitoes from Tanzania.
 The name”chikungunya”is derived from the native word for the disease in
which the patient lies “doubled up” due to severe joints pain.
 Epidemics of chikungunya have occurred in many African countries.

162. Togaviruses
 Togaviruses are spherical enveloped viruses with 50-70 nm in diameter,
with a single stranded RNA.
 The family Togaviridae contains besides arboviruses belonging to genus
Alphavirus, genus Rubivirus(rubella virus)
 Alphaviruses are mosquito-borne viruses, they are transmitted by culex
and anopheles mosquitoes
 The virions are about 70 nm in diameter and contain an envelope.
 The family Togaviridae contains two genera: Rubivirus and Alphavirus
 Rubella is rare in developed countries because of an effective vaccine.
 Alphavirus: This genus contains about 25 viruses, all of which are
transmitted by arthropods.

163. Paramyxoviridae
The family paramyxoviridae contains viruses responsible of acute
respiratory infection(RSV and parainfluenza viruses) and also two of the
most contagious diseases of chilhood(Measles and Mumps)
Morphology:
 They are spherical in shape, vary in size from 100-300 nm, sometime
with long filaments and giant form upto 800 nm.
 The genome is linear, single stranded RNA.
 The nucleocapsid is surrounded by a lipid envelope which has the matrix
(M) protein at its base and two types of transmembrane glycoprotein
spikes at the surface.
 It is also responsible of the cell to cell fusion, causing large giant cells or
syncytia, which which are the characteristic of paramyxoviruses
infections.
 The F protein also mediate the hemolytic activity of paramyxoviruses

164. Classification and properties of paramyxoviridae
Genus
Property Parainfluenzavirus Mumps Morbillivirus Pneumovirus
Human viruses Parainfluenza 1-4 Mumps Measles RSV
Diameter of nucleocapsid 18 nm 18 nm 18 nm 13 nm
Fusion(F) protein present present present present
Hemolysin present present present absent
Hemagglutin/hemadsorption present present present absent
Neuraminidase present present absent absent
Intracellular inclusions in
cytoplasm(C)/nucleus(N)
C C N, C C

165. Rubulavirus(Mumps virus)
 Mumps is an acute infectious disease commonly affecting
children and characterised by nonsuppurative enlargement of
the parotid glands.
Properties:
 Mumps virus is a typical paramyxovirus possessing both HN
and F proteins
 It agglutinates the erythrocytes of fowl, guinea pigs, humans
and many other spp.

167. Laboratory diagnosis and Prevention
 Specimens: saliva(within 4-5 days), urine(up to two weeks), CSF(8-9
days) after the onset of illness.
 Prevention :The Jeryl-Lynn strain of mumps virus(live
vaccine), attenuated by passage in eggs and grown in chick
embryo fibroblast culture is used as a vaccine.
 It is recommended only after one year of age as maternal
antibodies may interfere with the multiplication of the vaccine
virus if given earlier.
 The vaccine is given as a single subcutaneous injection, either
alone or in combination(MMR vaccine).
 It provides protection at least for ten years.

168. Parainfluenza viruses
 There are four types of parainfluenza viruses(1-4)
Clinicla features:
 Parainfuenza viruses are responsible of 10% of respiratory
infections in children.
 The most serious clinical disease is croup, which is mostly due to
types 1 and 2.
 Type 3 causes lower respiratory disease such as bronchitis,
bronchiolitis and pneumonia.
 Types 4 causes minor respiratory illnesses.
 In adults parainfluenza viruses cause sore throat
 Parainfluenza viral infection are confined to respiratory tract unlike
Mumps which is systemic disease

169. Respiratory Syncytial Virus(RSV)
 Because it caused cell fusion and formation of multinucleated
syncytia in cell culture, it was named respiratory syncytial
virus.
 It is now recognised as the most important cause of lower
respiratory tract infection in children, particularly in the first
few months of life.
Properties of the virus:
 RSV is pleomorphic, it has a size ranging from 150-300 nm.
 It is an enveloped virus, the envelop has two glycoproteins, the
G protein which the virus attaches to cell surface, and the
fusion F protein.

170. Respiratory Syncytial Virus(RSV)
Properties of the virus:
 The F protein is also responsible for cell to cell fusion, which
leads to the characteristic syncytial cytopathic changes in RSV
infection
RSV differs from other paramyxoviruses:
1. In not possessing the hemagglutin activity.
2. Does not have neuraminidase or hemolytic properties.
3. It has a smaller nucleocapsid(13nm)
4. RSV does not grow in eggs, it is grown in HeLa and Hep-2.
 It is highly labile, and is inactivated rapidly at room
temperature.

171. Measles
Morphology:
 It is spherical, pleomorphic particle, 120-250 nm in diameter,
tightly coiled helical nucleocapsid, surrounded by the lipoprotein
envelope carrying on the surface hemagglutinin(H) spikes
 The envelope also has the F protein, which mediate cell fusion and
hemolytic activities.
 Measles grows well on human or monkey kidney and human
amnion cultures, which are the preferred cells.
 Cytopathic effect consist of multinucleate syncytium formation with
numerous acidophilic nuclear and cytoplasmic inclusions,
multinucleate giant cells are also found in the lymphoid tissues of
patients.

172. Prophylaxis
 Normal human gammaglobulin given within 6 days of
exposure can prevent or reduce the disease.
 Gammaglobulin is useful in children with immunodeficiency,
pregnant woman and other at high risk.
 A safe and effective attenuated live vaccine is available
 The vaccine is either given alone or in combination at the
MMR vaccine
 A single subcutaneous injection of the measles vaccine
provides protection beging in about 12 days and lasting for
over 20 years.
 The vaccine is contraindicated, in immunodeficiency,
untreated tuberculosis and pregnancy.

173. IMPORTANT HUMAN HEPATITIS VIRUSES
Hepatitis A Hepatitis B Hepatitis C Hepatitis D Hepatitis E
Family Picornaviridae Hepadnaviridae Flaviviridae
Genome RNA DNA RNA RNA RNA
Transmiss
ion
Fecal-oral Parenteral,
blood, sexually,
needles,perinatal
Parenteral,
blood,needles
, perinatal
Parenteral,blood
,sexually,needles
,perinatal
Fecal-oral
Comments No chronic liver
disease, rarely
fatal, severity
increases with
age
5-10% chronic
hepatitis, linked
with
hepatocellular
cancer
Chronic
infections are
common
Coinfection/
superinfection
in patients
infected with
HBV
Wide range of
Clinical outcomes,
high mortality rate
in pregnant
women

174. HEPATITIS VIRUSES
Hepatitis A virus
Infections
 Infections are spread by the fecal-oral route and are generally
due to poor sanitation and hygiene. Food handling transmission is
common.
 Humans can also acquire the infection from contaminated shellfish,
including shrimp, oysters, scallops, etc.
 Vaccines are available.

175. Hepatitis C virus(HCV)
Morphological structure:
 HCV measure 50-60 nm in
diameter, with a linear single
stranded RNA genome.
 It has an envelope with
glycoprotein spikes.
 HCV resembles flaviviruses in
structure and organisation, has
been classified in the genus
Hepacivirus, family flaviviridae.
 HCV shows considerable genetic
and antigenic diversity, at least six
different genotypes and has many
subtypes, indacating high
mutability.

176. Clinical features and epidemiology
Mode of transmission:
1. Transfusion of blood and blood components
2. Other modes of contact with blood or blood products
3. Injectable drug abusers,
4. Transplantation
5. Sexual transmission
The incubation period is 2-25 weeks.
 The acute illness is mild or anecteric, Jaundice is seen in about 5%
of patients only.
 About 50 -80% of patients progress to chronic hepatitis.And some
patients develop cirrhosis and hepatocellular carcinoma

177. Laboratory diagnosis
1. The standard method of diagnosis is antibody detection by ELISA.
2. Identification of HCV RNA in blood is more sensitive and specific
results with fews days after infection.
3. Molecular method like PCR(nucleic acid amplification)
4. HCV antigen detection
5. Elevated liver enzymes
 The virus has not been grown in cell cultures
 Prophylaxis, blood screening is possible, no specific or passive
immunising agent is available
 Treatment, prolonged treatment with interferon alpha along with
ribovirin is useful.

178. Hepatitis E virus(HEV)
Morphology:
 HEV is spherical nonenveloped virus, 32-34 nm in diameter,
with a single stranded RNA genome.
 It resembles carciviruses, it has been provisionally classied in
the genus Herpesvirus, family caliciviridae
Clinicla features:
 The incubation period is 2-9 weeks, most cases occur in young
to middle aged group(15-40 years old), the disease is mild and
self limited, with low cases of fatality(1%).
 Clinical severity and high case fatality rate 20-40% are seen in
pregnant woman in the last trimester of pregnancy.

179. Hepatitis E virus(HEV)
Mode of transmission
 Faecal-oral route, by ingestion of food, drinks contaminated
by infected faeces.
 Carrier state has not been observed; it has been reported to be
prevalent in animal reservoirs such as pigs.

180. MEDICALLY IMPORTANT RNA VIRUSES
Human immunodeficiency virus(HIV)
Brief history:
 The emergency and pandemic spread of the acquired
immunodeficiency syndrome(AIDS) have posed greatest
challenge to public health.
 The full consequences of this phenomenon may not be evident
for several years due to the silent spread and slow evolution of
HIV infection.
 The first indication of this new syndrome came in 1981, with
reports from New York and Los Angeles(USA), of sudden
unexplained outbreaks of two very diseases, kaposi’s sarcoma
and pneumocystis carinii pneumonia in young adults who were
homosexuals or addicted to injected narcotics.

181. Human immunodeficiency virus(HIV)
Brief history:
 They appeared to have lost their immune competence, making
them vulnerable to fatal infections with relatively avurulent
microorganisms, and other malignancies.
 This condition was named acquired immunodeficiency
syndrome(AIDS).
 In 1983 Luc montagnier and colleagues from Pasteur institute,
Paris(France) isolated a retrovirus from a west African patient
with persistent generalised lymphadenopathy, which is a
manifestation of AIDS, and called it lymphadenopathy
associated virus(LAV).

182. Human immunodeficiency virus(HIV)
Brief history:
 In 1984, Robert Gallo and colleagues from National Institute
of Heath, USA, reported the isolation of retrovirus from AIDS
patients and called it human T cell lymphotropic virus-
III(HTLV-3)
 HTLV1 and HTLV2 have already been descrided earlier in
association with human T-cell leukemia.
 To resolve this nomenclature confusion the international
community of virus nomenclature in 1986 decided on generic
name of human immunodeficiency virus(HIV) for these
viruses.
 In 1985, serological tests(ELISA) became available for
detection of anti-HIV antibodies.

183. Human immunodeficiency virus(HIV)
 HIV, the causative agent of AIDS, belongs to the lentiviruses
subgroup of the family retroviridae.
Strucrure:
 HIV is spherical, enveloped virus, with 90-120 nm in diameter,
the nucleocapsid has an outer icosaehedral shell and an inner
cone-shaped core.
 The genome is composed of two identical single stranded
positive sense RNA copies, reverse transcriptase enzyme,
which a characteristic feature of retroviruses.
 When the virus infects a cell, the viral RNA is first transcribed
by the enzyme into single stranded DNA and then double
stranded DNA(provirus) which is integrated into the host cell
chromosome.

184. Major antigens of HIV
A. Envelope antigens:
1. Spike antigen-gp120 (principle envelope Ag)
2. transmembrane pedicle protein-gp41.
B. shell antigen:
1.nucleocapsid protein-p18
C.core antigens:
1. principle core antigen-p24
2. other core antigens-p15, p55
D. polymerase antigen-p31,p51,p66

186. Antigenic variation and diversity of HIV
 The original isolates of HIV and related strains prevalent all over
the world belong to HIV type1.
 HIV strains first isolated from West Africa in 1986, which react
with HIV type1 antiserum very weakly have been termed HIV
type2.
 The envelope antigens of the two types are different, though their
core polypeptides show some cross –reactivity.
 HIV-2 has 40% genetic identity with HIV-1, and it is less much
virulent than HIV-1.

187. Pathogenesis
Mode of transmission:
1. Sexual intercourse
2. Transfusion of blood and blood components
3. Needle prick injury.
4. Organ transplantation
5. Congenital transmission
 HIV virus attack CD4 lymphocytes principally but can infect any cell with
CD4 surface antigen.
 Thus about 5-10 % of B-lymphocytes 10-20 % of monocytes and
macrophages are susceptible.
 Specific binding of the virus to the CD4 receptor is by the envelope
glycoprotein gp120, however for infection to take place, cell fusion is
essential, is done by transmembrane gp41.

188. Pathogenesis
 Binding to the CD4 requires also a corereceptor molecule
CXCR4 of T cell and CCR5 for macrophages tropic strains.
 After fusion of the virus with the host cellmembrane, the HIV
genome is uncoated and internalise into the cell, viral reverse
transcriptase mediates transcription of its RNA into double
stranded DNA.
 The DNA is integrated within the genome of infected cell
through the action of viral integrase, causing a latent infection.
 Lytic infection is initiated releasing progeny virions which
infect other cells.
 The primary pathogenic mechanism in HIV infection is the
damage caused to CD4 T-lymphocytes.

189. Pathogenesis
 T cell decrease in numbers and the T4:T8 cell ratio is reversed.
 Viral infection can suppress the function of infected cells
without causing structural damage.
 Infected T4 cells do not appear to release normal amount of
interleukin-2, gamma interferon and other lymphokines.
 Thus due to damage of CMI, humoral immunity is also
affected, as helper T cell activity is essential for optimal B cell
function.
 An important feature of HIV infection is the polyclonal
activation of B lymphocytes leading to
hypergammaglobulinemia.

190. Pathogenesis
 All classes of immunoglobulin are involved but levels of IgG
and IgA are particularly raised.
 In infants and children IgM levels are also elevated.
 Allergic reaction occurs due to immune complexes(type3
hypesensitivity)
 The activity of NK cell and cytotoxic T lymphocytes is also
affected.
 Clinical manifestation in HIV infections are due not primarily
to viral cytopathology but secondarily to the failure of immune
response.
 This results in opportunistic infections and malignancies.

191. Clinical features of HIV infection
1. Asymptomatic or latent infection
 It is a phase of symptomless infection(clinical latency) which
may last up to several years.
 They show positive HIV antibodies during this phase, hence
are infectious.
 Patient show as minor opportunistic infection, persistent
generalised lymphadenopathy.
2.PGL is the presence of enlarged lymph nodes, at least 1 cm in
diameter that persists at least for 3 months, without any other
cause of illness.

192. Clinical features of HIV infection
3. AIDS related complex(ARC):
 This group includes patients with considerable immunodeficiency
and present symptoms or minor opportunistic infections
 Symptoms such as fatigue, unexplained fever, persistent diarrhoea,
marked weight loss, common opportunistic infections like
candidiasis, herpes zoster, salmonelosis, TB.
 Generalised lymphadenopathy and splenomegaly are usually
present.
 4. AIDS:this is the end stage disease representing the irreversible
breakdown of immune defense mechanisms leaving the patient
exposed to progressive opportunistic infections and malignancies

193. Laboratory diagnosis
A) Immunological tests:
 The total leucocyte count show leucopenia.
 The differential count show lymphocyte usually below
2000/cube mm
 The T4:T8 ratio is reversed,
 Raised IgG, IgM, and IgA levels(hypergammaglobulinemia)
B) Specific tests for HIV infection:
 Antigen detection, the major core antigen(P24), is the earliest
virus marker to appear in blood
 The appearance of P24 antigenemia and viremia followed by
IgM antibodies(4-6 weeks) response coincides with the acute
or seroconversion illness.