For the students learning Microbiology like MSc BSc MBBS Dental Nursing BPTH even those preparing for exams such as NEET

1. UNDER GARADUATE STUDENT’S LECTURE ON
BY
GUNJAL PN
ASSIST. PROF.
DEPT OF MICROBIOLOGY
DVVPF’S MEDICAL COLLEGE & HOSPITAL
AHMENDAGAR
Large Intestinal Nematodes:
Trichuris trichiura,
Enterobius vermicularis,
Trichinella spiralis
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2. Learning objectives
• At the end of this session/theory class students must able
to understand:
• General properties of Nematodes.
• Classification
• General description
• Large intestinal Nematodes
• Trichuris trichiura
• Enterobius vermicularis
• Tichinella spiralis
• Their morphological forms, life cycle, pathogenesis and
clinical manifestations, laboratory diagnosis, treatment and
prevention.
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3. General Properties
• Nematodes are probably the most widespread
animal group occurring in the world.
• Many – Non-pathogenic and exist as free living
forms in fresh and marine water and soil.
• Few species are pathogenic and exist as parasitic
form in animals, humans and plants.
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4. Classification
• Systemic Classification – Based on Anderson et
al (1974) Classification.
• Phylum: Nematoda
• Class: Adenophorea
• : Secernenta
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5. Differences between class
Adenophorea and Secernentea
Characters Class Adenophorea Class Secernentea
Sensory
Structure
Absent Present
Esophagus Modified with presence of
: Glands cells
(Stichocystes) or Reserve
Organ (Trophosome)
Normal appearance
Excretory organs Without lateral canals Lateral canals present
Caudal papillae Absent Present
Infective form to
the definitive
host
First stage larva
(Trichinella ) or
embryonated eggs
(Trichuris)
Third stage larva or
embryonated eggs
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6. Systemic Classification of
Phylum Nematoda (Anderson et al 1974)
Class Superfamily Family Genus
Adenophorea Trichinelloidea Trichinellidae Trichinella
Trichuridae Trichuris,
Capillaria
Secernentea Oxyuroidea Oxyuridae Enterobius
Ascaridoidea Ascarididae Ascaris,
Toxocara, etc.
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7. Classification based on habitat
• Most of the Nematodes are Inhabitat in the
intestine.
• While some (for e.g. filarial worms) reside in
various tissues.
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8. Classification based on habitat
Intestinal Human Nematodes Somatic Human Nematodes
Large Intestine
Trichuris trichiura
(Whip worm)
Enterobius vermicularis
(Thread worm)
Other Human Somatic nematodes
Trichinella spiralis
Dracunculus medinensis
(Guinea worm)
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9. Classification based on they lay eggs
or larva
• Based on they lay eggs or larvae after
fertilization, nematodes can be classified into:
• Oviparous
• Viviparous
• Ovoviviparous
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10. Oviparous
• Most nematodes are oviparous, i.e. following fertilization, the
female worms produce eggs that takes some time to hatch out to
form larvae in the environment.
• Eggs with segmented ovum – Hookworm and Trichostrongylus spp.
• Eggs with unsegmented ovum- Ascaris spp.
• Eggs with unsegmented ovum with mucus plug at both the poles –
Trichuris trichiura and Capillaria spp.
• Eggs containing larvae that take some time to hatch out –
Enterobius vermicularis.
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11. Viviparous
• Female worm directly give birth to larvae;
there is no egg stage.
• Filarial worms , Trichinella species,
Dracunculus species.
• Female worms lay eggs containing larvae that
immediately hatch out.
• For e.g. – Strongyloides species.
Ovoviviparous
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12. General description
• Nematodes pass through six developmental
stages.
• Adult worm, egg stage, and four larval stages
(L1-L4).
• Each larval stage transform to next by
shedding cuticle called Moulting.
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13. Developmental Stages of Nematodes
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14. Adult Worm
• Shape:
• Nematodes are long, cylindrical or filariform in shape
with both ends pointed.
• They are unsegmented without any appendages
• Size:
• Variable, ranging from less than 5mm (Hookworm,
Trichinella ) to as long as 1 meter (Dracunculus).
• Female worms are longer than male worms.
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15. Adult Worm
• Symmetry:
• Body is bilaterally symmetrical.
• Body wall:
• Made up of outer layer of tough acellular cuticle and inner layer of
longitudinal muscle.
• Locomotion:
• Nematodes move by contraction of the longitudinal muscles.
• Alimentary Cannel:
• Well developed consist of mouth at anterior end followed by muscular and
glandular esophagus, intestine and rectum that leads to sub terminal anus
at posterior end.
• In some mouth bears teeth – Hookworm
• The esophagus (or pharynx) may be posterior bulb – Enterobius.
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16. Adult Worm
• Body cavity / Pseudocele :
• Space between body wall and alimentary canal, with high
hydrostatic pressure.
• Filled with body fluid secreted by intestine and genital
organs.
• Sexes:
• Nematodes are diecious (bisexual), i.e. sexes are different.
• Male Reproductive system:
• Has a long convoluted tube – differentiated into testes, vas
deferens, seminal vesicle and ejaculatory duct.
• Some may also bear accessory copulatory organ
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17. Adult Worm
• Female Reproductive system:
• Has two (common) or one convoluted tube.
• Each tube is differentiated into ovary, oviduct, seminal receptacle, and
uterus and then both the tubes joined to form a common vagina, opens
outside through vulva (genial pore).
• Nervous System:
• It is rudimentary and has circular nerve ring (brain) surrounding the
esophagus and six longitudinal nerve trunks.
• Dorsal nerve – motor control
• Lateral nerve – sensory control
• Ventral nerve – combines both functions
• Excretory System:
• Excretion of nitrogenous waste in the form of ammonia through body wall.
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18. Adult Male and Female Nematode
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19. Life cycle
• Nematodes complete their life cycle in one
host (Human) except in filarial worms (need
two hosts – definitive host – man and
intermediated host – mosquito.
• Life cycle, pathogenesis, clinical
manifestations, laboratory diagnosis discussed
in detail under individual nematodes.
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20. Trichuris trichiura
• Also known as “Whip worm” – adult
worm resembles to a handle of a whip.
• First described by Linnaeus in 1771.
• 71 species of Trichuris trichiura are
recorded. Human infection confined to
T. trichiura and rarely T. suis (pig whip
worm) T. vulpis (dog whip worm).
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21. • Habitat :
• Resides in large intestine of
human (mainly cecum and
appendix).
• Epidemiology:
• Trichuriasis is world wide
in distribution – warm
and moist climate.
• Children are commonly
affected.
• Global prevalence -
604 million.
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22. Morphology
• Adult worm:
• It is whip shaped.
• Anterior three fifth is thin, hair like, (rope
of a whip) and posterior two fifth is short
and thick and coiled.
• Male is whitish – 30 - 45mm long and
bears a coiled posterior end.
• Female – longer 35 - 50mm and posterior
part is either shaped like a comma or a
arc (resembling handle of a whip).
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23. Egg
• Eggs are barrel shaped surrounded
by a shell, bear mucus plug at both
poles.
• Elongated, measures 50-54 um
long and 22-23 um wide.
• Unembryonated when freshly
passed.
• Bile stained : Yellowish brown in
colour (in saline mount).
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24. 9/21/2021 Dept of Miicrobiology 24

25. 9/21/2021 Dept of Miicrobiology
Trichuris trichiura (Whip Worm)
Adult worm 30 – 50 mm
Eggs 60 µ, bile stained
Barrel-shaped with Mucus plug
at each pole
Unsegmented ovum
Infective
form
Mature embryonated eggs
Mode of
transmission
Ingestion
Site of localization Large intestine -
caecum
25

26. Life cycle
• Host: Human are the only hosts.
• Infective form: Embryonated eggs.
• Mode of transmission: Ingestion of contaminated food and
water containing embryonated eggs.
• Egg Larva Adult Transformation:
• Eggs hatch out in intestine –
• Releasing the second stage larva,
• Larvae - migrate to large intestine –
• Undergo further molting to transform into – adult.
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27. Life cycle
• Adults laying Unembryonated eggs :
• Within 2-3 months, female following fertilization start laying
unembryonated eggs.
• Each female can lay – 14,000 -20,000 eggs per day for 1-3 years.
• Embryonation:
• Unembryonated eggs passed in feces – non infective.
• It takes about 28 days to become embryonated.
• It undergoes two molts to produce second stage larva with egg shell.
• Embryonation occurs at 250C in warm moist condition.
• Such embryonated eggs are infective to humans.
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28. 9/21/2021 Dept of Miicrobiology 28

29. Life cycle
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30. 9/21/2021 Dept of Miicrobiology
• Infection – Trichuriasis
• Symptoms depend on worm burden
– Less than 10 worms – asymptomatic
– Heavier infections –
1. chronic profuse mucus and bloody diarrhea with
abdominal pains and edematous rectum
2. malnutrition, weight loss and anemia
3. Allergic Response by host increased numbers of
macrophages infiltrates in lamina propria that
produces tumor necrosis factor – α (TNF-α).
30
Pathogenicity and Clinical Feature

31. 9/21/2021 Dept of Miicrobiology
• Common Manifestations include:
• Abdominal pain
• Anorexia
• Trichuris dysentery syndrome - Bloody or mucoid diarrhea
resembling inflammatory bowel disease.
• Iron deficiency anemia - due to blood loss.
• Recurrent rectal prolapse - due to heavy worm load in the
rectum and malnutrition.
• Growth retardation and impaired cognitive function - due
release of anti-inflammatory cytokines induced by the
secretory molecules of parasite.
31
Pathogenicity and Clinical Feature

32. Laboratory Diagnosis
• Because the level of egg output is high approximately 200 eggs/gm
of feces per worm pair.
• Microscopic examination of a single Fecal smear is sufficient for
diagnosis of symptomatic case.
• The characteristic 50 X 22um barrel shaped Trichuris eggs with
mucus plugs at both the ends are readily detected on stool
examination either by direct wet mount or by stool conc. methods.
• Preservatives: Formalin is preferred.
• Whip shaped adult worms of 3 – 5 mm size are occasionally seen on
proctoscopy -
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33. 9/21/2021 Dept of Miicrobiology
Laboratory diagnosis & Treatment
• Stool examination – Bile stained eggs with
bipolar mucus plugs
• Treatment – Albendazole – (400 mg daily
for three doses / Mebendazole – 500mg
once.
• Ivermectin – 200mg/kg daily -3 doses –
safe – less effective.
• Prevention –
– Proper disposal of night soil
– Prevention of consumption of uncooked
vegetables & fruits .
33

34. 9/21/2021 Dept of Miicrobiology 34

35. Introduction
• Also know as “Pin worm” or
“Thread worm”.
• Described first by Leuckart, in 1865.
• E. vermicularis is the only species.
• Habitat : Adult worm remains
attached to the large intestine
(cecum, appendix and adjacent
portion of colon) by their mouth
end.
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36. Epidemiology
• Global prevalence in humans : 209 million cases.
• Maximum prevalence – school going kids 5 -14
yrs.
• People carry the infection for years together due
to auto infective cycles.
• Factors promoting infection: Over crowding and
impaired hygiene, poor personal care (nail biting
or inadequate hand washing).
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37. Morphology
• ADULT WORM:
• Small, white, thread like – “Threadworm”.
• Cervical alae: A wing like expansion of
cuticle near anterior end.
• Double bulb esophagus: Posterior end of
esophagus is dilated to form globular bulb.
• Male : smaller, 2-5mm X0.1-.02 mm long .
Dies soon after fertilization.
• Female : Longer, 8-13 mm X 0.3-0.5mm
long. Looks like pin hence “Pin worm”.
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38. Morphology
• EGGS:
• Shape: Oval or plan convex – one side is
plan other is flat – laterally compressed.
• Size: 50 – 60 um long X 20 – 30 um wide.
• Surrounded by:
• Double walled egg shell.
• Not bile stained
• Colourless in saline mount.
• Embryonated eggs when freshly passed
in stool – has tadpole larva inside.
• Floats in saturated salt solution.
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39. 9/21/2021 Dept of Miicrobiology
Enterobius vermicularis
Adult worms Male 2 - 5 mm
Female 8 -13 mm, oviparous
Eggs 60 µ, non bile stained
Plano-convex with coiled
embryo
Infective
form
Embryonated egg
Mode of
transmission
Ingestion,
Autoinfection
Site of localization Large intestine –
caecum & appendix
(Pin Worm, Seatworm)
39

40. Life cycle
• Host: Humans are the only hosts.
• Infective form: Embryonated eggs are infective form to
humans.
• Mode of transmission: Men usually children acquire
infection by ingestion of embryonated eggs containing
larva by :
• Ingestion of embryonated eggs containing larva. With
contaminated fingers due to inadequate washing of
hands or nail biting.
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41. Life cycle
• Auto-infection:
• Endogenous autoinfection: by retrograde
migration of the larva hatched from the eggs in the
peripheral skin.
• Exogenous autoinfection : eggs cause intense
irritation of the perianal skin and scrapping of the
area leads to contaminated finger .
• Rarely inhalation of air born eggs.
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42. Life cycle
• Development in Man:
• Eggs usually have fully developed larvae – eggs hatched out – larvae
released in cecum – developed into adult worms.
• Adult female matures within 1 month – Male dies after fertilizing
female – gravid female filled with eggs – migrates to large intestine
(rectum, colon) – start laying eggs on perianal skin.
• Adult female lays – 2,000 eggs/day.
• Eggs are embryonated and are infective to other humans.
• Female worm can survive upto 2 months but due to auto infection
cycle continues.
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43. 9/21/2021 Dept of Miicrobiology 43

44. 9/21/2021 Dept of Miicrobiology
Life cycle – E. vermicularis
44

45. 9/21/2021 Dept of Miicrobiology 45

46. Pathogenicity and Clinical Features
• Asymptomatic : Most cases are asymptomatic.
• Symptomatic Cases: Females, children.
• Cardinal Symptoms :
• Perianal pruritus often worse at night as a result of
nocturnal migration of female worm.
• Excoriation of perianal skin and bacterial superficial
infection may occur – due to continuous scratching of skin.
• Abdominal pain and weight loss – in heavy infections.
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47. Pathogenicity and Clinical Features
• Migration of the worm:
• Rarely, pinworms invade the female genital tract, causing
vulvovaginitis and pelvic or peritoneal granulomas.
• Other sites involved are – Urinary tract, peritoneal cavity,
lungs and liver.
• Eosinophilia is uncommon.
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48. Laboratory Diagnosis
• Female worm lays eggs in perianal area and not in rectum.
• Hence eggs are not readily detected in stool.
• So eggs deposited in perianal area are collected with the help of
cellophane tape or its modification – NIH – National Institute of
Health, USA developed swab method.
• Cellophane tape – Eggs are collected and detected by microscopic
examination.
• After applying clear cellulose acetate tape to perianal region in
morning before child defecate.
• Tape is then applied to clear glass slide and observed in microscope.
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49. Laboratory Diagnosis
• NIH Swab – developed by National Institute of Health, USA.
• Consist of a glass rod attached to a cellophane tape by a rubber
band.
• Other end of it is fixed with rubber stopper and kept in a test
tube.
• Cellophane tape part of it is rolled over the perineal and perianal
skin to collect specimen.
• After tape is transferred to a slide, microscopic examination will
detect E. vermicularis eggs – Plano convex, flattened, 50 -60 um
X 20 -30 um containing larvae inside it.
• Adult female occasionally be found in feces or crawling to the
perianal skin
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50. 9/21/2021 Dept of Miicrobiology
Laboratory Diagnosis & Treatment
• Detection of adult worms
in-
– Feces
– Perianal region
• NIH swab – scrapings from
perianal region
• Microscopy – non bile
stained eggs
• Mebendazole
50

51. Prevention
• Improved personal hygiene.
• Proper washing of cloths – Bedsheets.
• Proper toilet hygiene.
• Cutting of nails regularly.
• Avoid of nail biting habits.
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52. 9/21/2021 Dept of Miicrobiology 52

53. 9/21/2021 Dept of Miicrobiology
Trichinella spiralis (Trichina Worm)
Adult worms (smallest
nematode infecting man)
Male 1.4 – 1.6 mm
Female 3 - 4 mm, viviparous
Infective form Encysted larvae (100µ) in
striated muscles of pig
Mode of transmission Ingestion of improperly
cooked pork
Site of localization Small intestine
Commonly involved
muscles
Diaphragm, Intercostals, Deltoid,
Pectoralis major, Biceps
53

54. Life cycle
• Host:
• Pig is the optimum host and the principal reservoir of infection.
• Animals like rats, horses or other carnivores can also serves as host.
• Transmission – In nature it occurs from one flesh eating to other.
Common cycles are pig to pig, rat to rat, pig to rat.
• Man is accidental host and acts as dead end.
• Infective Form: First stage (L1) Larvae.
• Mode of transmission – Ingestion of raw undercooked pork or other
animal meat containing L1 larvae.
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55. Life cycle
• INTESTINAL PHASE :
• L1, larvae transforms to adult:
• Ingested L1 larvae immediately freed from the animal flesh by
the digestive enzymes in stomach.
• Then, carried to small intestine – penetrate intestinal mucosa
– undergo – four moults – develop into – adult worm in 2-3
days.
• Female worms lay L1 larvae- Male worms mate with female
and die.
• Females – viviparous
• After 5 days of fertilization – start laying – first stage larvae.
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56. Life cycle
• MIGRATION PHASE :
• L1 larvae – penetrate intestine – carried to skeletal muscle – via –
lymphatic and venous circulation.
• ENCYSTMENT :
• L1 larvae enter inside skeletal muscle cells and behave as obligate
intracellular anaerobic parasite.
• Secretion of oesophageal glands modulates the host DNA to alter the
hostile environment.
• Muscle cells are modified within 20 days to form “Nurse cells”
surrounded by blood vessels – providing required environment for
containment of parasite for years.
• Only skeletal muscle cells are infected, encystment does not occur in
cardiac and smooth muscles.
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57. 9/21/2021 Dept of Miicrobiology
Encysted larva in pig
muscles (infective form)
Eating under-
cooked pork
Larva released
in small intestine
Develop into
adult worms(male
dies )
Female deposits
larva in intestinal
mucosa
Larva enters
circulation
Larva deposit
and encyst in
striated muscles
(remain viable for many years, or
get calcified & die )
Life Cycle – T spiralis
40 hrs
57

58. 9/21/2021 Dept of Miicrobiology
Pathogenicity
• Trichinelliasis / Trichinosis – clinical features depends on the
stage:
1. Stage of intestinal invasion: 5-7 days, pain in abdomen, nausea,
vomiting, diarrhoea
2. Stage of larval migration: fever, urticarial rash, splinter
hemorrhages, periorbital & facial edema
3. Stage of encystation: asymptomatic in light infections; myalgia,
weakness in heavy infections
• Complications – during migration:
– myocarditis, encephalitis
58

59. 9/21/2021 Dept of Miicrobiology
Laboratory Diagnosis
• Muscle biopsy – encysted
larva
• Blood – eosinophilia
between 2nd & 4th week
• Serology – to detect specific
Abs by:
1. Bentonite flocculation test
2. Latex agglutination test
59

60. 9/21/2021 Dept of Miicrobiology
Treatment & Prevention
Treatment
• Thiabendazole &
Mebendazole – adult
worms
• Corticosteroids –
complications
Prevention
• Proper cooking of pork or
proper storage
• Avoidance of feeding bits &
refuse from slaughter
houses & farms to pigs –
breaks life cycle.
60

61. 9/21/2021 Dept of Miicrobiology
Key to the diagnosis of Intestinal Nematodes
Intestinal
Nematodes
Larvae in Stool
S. stercoralis
Eggs in stool
Colored
(Bile Stained)
A. lumbricoides
T. trichiura
Colorless
(Non Bile Stained)
A. duodenale
N. americanus
E. vermicularis
Eggs on
Perianal Skin
Colorless
(Non Bile Stained)
E. vermicularis
61

62. Expected Question
• Classify Nematodes. Describe life cycle,
pathogenicity and laboratory diagnosis of –
• Trichuris trichiura
• E. vermicularis
• T. spiralis .
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63. Thank you!
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