Intestinal parasites causing infection

1. NEMATODA
•Are round worms
•Consist of a large assemblage of worms with a
relatively simple structure
•Have a worldwide distribution
•Majority are free living in soil or water and a few
are parasitic in all classes of vertebrates
•The parasitic species are giants, some up to
several feet in length and some may have
complicated life cycles

3. Some examples

4. General characteristics
• Elongated and cylindrical tapering at both extreme ends
• Are encased in a very tough and impermeable transparent
cuticle
• The cuticle is marked externally by fine transverse striations
or bristle, spines, ridges or expansions of various kinds
• Have a spacious body cavity known as a pseudocoelom in
which the reproductive organs lie.
• The nervous system consists of a nerve ring around the
oesophagus from which longitudinal nerve trunks run
forwards and backwards.
• Special sensory organs at the anterior end called amphids and
in some species there is a pair of similar sensory organs
situated at the posterior end called phasmids.
• There are also tactile sensory organs around the mouth and a
pair in the neck region and these are called deirids
• Sexes are separate, males usually smaller than females

5. Trichiuris trichiura
• Are the whip worms or thread worms
• Its whiplike in form having a thick posterior
part of the body containing the reproductive
organs and a longer lash-like anterior occupied
only by the slender oesophagus.
• Also called trichocephalus
• Habitat: caecum and large intestines of many
animals including dogs, rodents, pigs, all sorts
of ruminants, man and monkeys

6. Morphology
• Measures 30-50mm in length of which the
thread like oesophageal region occupies two
thirds.
• Mouth has no lips but has a minute spear
• Males a little smaller than females
• Males have a curled tail
• Eggs are barrel shaped

7. Life cycle

8. Life cycle
• Has a very simple life cycle
• Eggs develop slowly and are less resistant to
dessication
• When embryonated eggs are swallowed, they
hatch near the caecum
• Then embryos burrow into the villi for afew days
• Finally, they take their residence into the caecum,
appendix and rectum where they mature in
about a month.
• After mating, females start to produce eggs which
are voided along with faeces.

9. EPIDEMIOLOGY
• A high incidences of Trichiuris infection is
always associated with an abundance of
moisture in the soil
• Heavy and well distributed rainfall or dense
shade.
• Infection may result from polluted moist soil.

10. Pathology
• If only a few worms are present, it does not produce
pathological effects.
• Under heavy infestation, hookworm disease results.
Symptoms
– Loss of appetite
– Nausea
– Diarrhea
– Blood streaked stool
– Weakness
– Loss of weight
– Anaemia
– Eosinophilia-increased white blood cells in circulation
– Abdominal discomfort
– Emaciation and sometimes fever
– In chronic cases, there is prolapse of rectum

11. Diagnosis
• Finding barrel shaped eggs in faeces or stool
• Concentration technique
Chemotherapy
• Trichiuris trichiura is difficult to eliminate because
of its remote position in the caecum which is far
from either the mouth or anus.
• Therefore, most antihelminthics are not effective
but the following can be used:
1. Latex
2. Enema
3. Dithiazanine

12. Trichinella spiralis (Trichnosis)
• It causes trichinosis - a cosmopolitan infection.
• Major reservoir host for human infections is
swine.
• Morphology:
– Adult female worm measures 3-4 mm in length
– Adult male worm measures 1.4-2.6 mm in length.
– The encysted larvae measure 800-1300 μm in
length.

14. Life cycle
• After ingesting infected meat, the capsule of the
encysted larvae is digested by gastric juice
• Larvae are released in the duodenum or jejunum
• They molt four times to become adult worm.
• After mating, the male worm dies and the female
worm begins to deliver the embryos 4-7 days
after the infection.
• Larvae penetrate the intestinal wall and migrate
through the lymphatic vessels to the blood
stream, which carries them to various organs.
• Skeletal muscles and diaphragm are most
frequently parasitized.
• Others include the tongue, masseter and ocular
muscles.

15. Life cycle

16. Clinical features
Two clinical phases:
1. The intestinal phase: lasting 1-7 days -
asymptomatic; sometimes cause nausea,
vomiting, diarrhea, constipation, pain, etc,
2. The muscle phase: causes myalgia, palpabral
edema, eosinophilia, fever, myocarditis,
meningitis, bronchopneumonia etc.

17. Diagnosis
• Muscle Biopsy
• Detection of larvae in blood or CSF
• Detection of larvae and adult worms in stool
(rare).
• ELISA
Treatment - Thiabendazole
Prevention
• Cooking of all meat before consumption
• Inspection of pigs
• Pork must be stored at -150C for 20 days.

18. HOOK WORMS
There are two species of hookworm:
1. Ancylostoma duodenale
2. Necator americanus
• The adults are found in the small intestines of
man.

19. Ancylostoma duodenale
• Grayish-white in color.
• Body is slightly ventrally curved.
• Distribution: the northern part of the world
including China, Japan, Europe, North Africa
and Ethiopia.
Morphology
• The male measures 10 cm in length.
• The female measures 12 cm in length.

20. Life cycle
• Eggs are passed in the stool, and under favorable conditions (moisture,
warmth, shade),
• larvae hatch in 1 to 2 days.
• The released rhabditiform larvae grow in the feces and/or the soil,
• After 5 to 10 days (and two molts) they become filariform (third-stage)
larvae that are infective.
• These infective larvae can survive 3 to 4 weeks in favorable environmental
conditions.
• On contact with the human host, the larvae penetrate the skin and are
carried through the blood vessels to the heart and then to the lungs.
• They penetrate into the pulmonary alveoli, ascend the bronchial tree to
the pharynx, and are swallowed.
• The larvae reach the small intestine, where they reside and mature into
adults.
• Adult worms live in the lumen of the small intestine, where they attach to
the intestinal wall with resultant blood loss by the host.
• Most adult worms are eliminated in 1 to 2 years, but the longevity may
reach several years.

22. Pathogenesis
• A.duodenale (third-stage) larvae follow thermal gradients and are
guided by heat to human skin where they may irritate or invade the
skin.
• A pruritic, erythematous, papular rash develops and produces what
is known as “ground itch” around penetration sites of the infective
larvae, usually on the hands and feet.
• Invasive infection occurs when larvae enter the bloodstream and
are carried to the lungs.
• A mild cough and pharyngeal irritation may occur during larval
migration in the airways; however, passage through the lungs is
usually asymptomatic.
• The larvae are swallowed down the oesophagus and migrate to the
gastrointestinal tract.
• Larvae then hook onto the intestinal mucosa where they mature
into adult hookworms by feeding on blood.
• The major-hookworm related injury occurs due to intestinal blood
loss, which can lead to iron-deficiency anaemia in moderate to
heavy infections.

23. Pathogenesis cont’d
• In the gut, adult worms may produce epigastric pain and
abnormal peristalsis.
• Clinical features are highly dependent on worm burden and
dietary iron levels.
• In children this condition may precipitate heart failure or
kwashiorkor.
• Retardation of mental, sexual, and physical development has
also been noted in children.
• Intrauterine growth retardation, prematurity and low birth
weight among newborns born to infected mothers has been
noted.
• Acute/heavy infections may result in fatigue, weakness,
abdominal pain, and diarrhea with blood loss.
• Adult’s lifespan in human intestine is 1-2 years but can be as
long as 10-12 years

24. Epidemiology
• Temperature is a prime controlling factor
• Rainfall is also fundamental: when soils dry up after a shower or as
faeces dry up, some of the larvae escape desiccation b y going
down the surface
• Clay or sandy soil is bad for survival of hookworm larvae but humus
soil is favorable.
• Soil impregnation by salt is injurious to the larvae
• Excessive rainfall is also not favorable but moderate rainfall
• Vegetation and dense shade are favorable for larvae survival
• Animals which feed on faces are injurious to larvae
• Age and sex of man; youngones are more susceptible than adults
because of soft skins and habit of playing with soil; females are
more susceptible than males
• Occupation: mining and agriculture are more susceptible
• Wearing of shoes
• Poor sanitation
• Expectoration habits:

25. Diagnosis
• Examination of stool by direct saline smear to
detect the eggs.
• Treatment: Mebendazole: 1 tab 2x daily for 3
days.
• Larval migrans
• Visceral larva migrans