Phylum Nematoda. Roundworms

1. 1
Theme: Medical helmintology.
Phylum Nematoda - Roundworms.

2. 2
1. Bilaterally symmetrical, elongate, unsegmented
worms.
2. Cylindrical, round in cross sections
(Roundworms).
3. Separate sexes. Sexual dimorphism: 1) males are
smaller than females; 2) posterior end of male worm
is rounded.
4. Pseudocoel containing body fluid.
5. Body wall is made by 3 layers:
a). Outer laminated non-cellular cuticle.
b). Subcuticular epithelium (hypodermis);
c). Muscle layer (4 groups of longitudinal cords).
Phylum Nematoda: general description

3. 3
• 6. Digestive system: mouth, pharynx,
oesophagus, intestine, anus (opens to cloaca).
• 7. Excretory system: special cells which function
as glands and systems of excretory canals.
• 8. Nervous system: peripharyngeal nervous ring,
dorsal and ventral longitudinal nerve cords.
• 9. Reproductive system:
a). Male reproductive organs: testis (long
convoluted tube), vas deferens, seminal
vesicle, ejaculatory duct (opens to cloaca).
• b). Female reproductive organs: two ovaries
(convoluted tubes), oviducts, uteri, vagina, vulva.

4. 4
Parasite: Ascaris lumbricoides
Disease: ascariasis
Distribution: Worldwide
Morphology: Adult worms are creamy
or pink, spindle-shaped, covered by
striated cuticle. Adult male about 20
cm in length, posterior end curved
ventrally, adult female about 25-40 cm
in length, posterior end straight.
Eggs are brown, oval, covered by
membranes. An external membrane is
tuberous.
Host: man
Way of transmission: fecal-oral
(alimentary).
Infective stage: eggs
Localisation: small intestine (adult),
liver, lungs, heart (larvae).

5. Sponsored
Medical Lecture Notes – All Subjects
USMLE Exam (America) – Practice

6. 6
1.Immature eggs pass in the
feces (200,000 eggs/day).
2.Under favourable environmental
conditions (temperature 20-25 °C,
oxygen, humidity 70-90%) larvae
develop inside the eggs in the soil
within 24 days (infective stage).
3.Eggs may be ingested through
contaminated, water or raw vege-
tables, hands. Eggs hatch in the
small intestine.
4.Larvae migrate through the gut
wall into the bloodstream and then to
the liver, heart, lungs. They enter the
alveoli, pass up the bronchi and
trachea, and are swallowed.
5.Within the small intestine, larvae
become adult worms.
6.Eggs appear in feces about 2
Life cycle of Ascaris lumbricoides

7. 7
Clinical manifestation:
1) Migrating larvae may lead to pneumonia, eosinophilia.
2) Adults in the intestine may cause intestinal obstruction,
penetration of the intestinal wall, occlusion of the bile
duct, the pancreatic duct or the appendix, toxic effects
(nausea, vomiting). Most infection are asymptomatic.
Laboratory diagnostics: microscopic examination of
feces (availability of eggs);
larvae may be found in sputum.
Prevention: washing hands before meals;
proper washing of vegetables eaten raw;
treatment of patients;
health education.

8. 8
Ascaris lumbricoides

9. 9
Parasite: Enterobius
vermicularis - Pinworm
Disease: enterobiasis
Distribution: Worldwide
Morphology: Adult female worms
are up to 10 mm in length, and male
worms are up to 5 mm. Eggs are
transparent and colourless,
asymmetrical, have thin and smooth
membrane, 40-60 μm.
Host: man.
Way of transmission: fecal-oral
(alimentary).
Infective stage: eggs.
Localisation: large intestine
(caecum).
MaleFemale

10. 10
Life cycle of Enterobius vermicularis
• 1.The adult pinworms live in the colon
approximately 30 days.
• 2.After fertilisation female worm
migrates from the anus and releases
thousands of fertilized eggs on
perianal skin.
• 3.Within 6 hours, eggs develop into
larvae and become infectious.
• 4.Reinfection can occur if they are
carried to the mouth by fingers after
scratching of the itching skin.
• 5.Clinical manifestation: Infection is
frequent among children. Perianal
pruritus (itching) is most common
symptom.
• 6.Laboratory diagnostics: the eggs
are recovered from perianal skin by
using the “Scotch tape” technique and
can be microscopically.
• 7.Prevention: keep sanitary condition,
dehelminthization of the population.
External
environment

11. 11
Parasite: Trichuris trichiura - Whipworm
Disease: trichocephaliasis (whipworm infection)
Distribution: Worldwide
Morphology: Adult female worms are up to 5,5
cm in length, and male are up to 4 cm. The front
end of the body is thread-like extend. The eggs
are brown, barrel-shaped with a plug at each end,
20-50 μm in size.
Host: man
Way of transmission: fecal-oral (alimentary)
Infective stage: eggs
Localisation: caecum, appendix, first 1/3 part of
large intestine.
Clinical manifestation: adult worms burrow their
hairlike anterior ends into the intestinal mucosa.
They feed blood. Trichuris may cause diarrhea,
abdominal pain, nausea, acute appendicitis. Most
infections are asymptomatic.
Laboratory diagnostics: microscopic
examination of feces (availability of eggs).
Prevention: washing hands before meals; proper
washing of vegetables eaten raw; treatment of

12. 12
1. Immature eggs pass in the
feces (2,000 eggs/day).
2. Larvae develop inside the
eggs under favourable environ-
mental conditions (temperature
26-28 °C, oxygen, humidity 80-
90%) in the soil within 4 weeks
(infective stage).
3. Embryonated eggs may be
ingested through contaminated,
water, raw vegetables and
hands.
4. Eggs hatch in the small
intestine; larvae become adults
in few days, then migrate to the
large intestine.
Life cycle of Trichuris trichiura

13. 13
Parasites: Ancylostoma duodenale -
Hookworm
Disease: ancylostomiasis
Distribution: Middle East, North
Africa, India, Southern Europe
(formerly).
Morphology: Adult worms about 1 cm
in length;
Eggs are trans-lucent, oval with blunt
poles, 40-60 μm in size;
Rhabditiform larva is about 0.25-0.5
μm with rhabditiform oesophagus (1/3
body length), pointed tail end;
Filariform larva is about 0.6-0.7 μm
with cylindrical oesophagus (1/4 body
length), sharply pointed tail.
Host: man
Way of transmission: penetration of
skin by filariform larva
Buccal capsule
of Ancylostoma duodenale

14. 14
1. Filariform larvae penetrate the skin, usually
of feet or legs in moist soil.
2. They are carried by the blood to the lungs,
migrate into the alveoli and up the bronchi
and trachea, and then are swallowed. They
develop into adults in the small intestine,
attaching to the wall with teeth. They feed
blood.
4. Immature eggs pass in the feces about 2
months after infection.
5. Eggs develop into rhabditiform larva and
into filariform larvae (infective stage) under
favourable environmental conditions in the
soil.
6. Clinical manifestation: 1)invasion stage:
dermatitis and itching (“ground itch”);
2)migration stage: pneumonia, eosinophilia;
3)intestinal stage: anemia, diarrhea,
abdominal pain, nausea.
7. Laboratory diagnostics: microscopic
examination of feces (availability of eggs).
Blood in the stool is frequent.
8. Prevention: disposing of sewage properly
Life cycle of
Ancylostoma
duodenale

15. 15
Parasite: Strongyloides
stercoralis - Threadworm
Disease: strongyloidiasis
Distribution: Worldwide
Life stages: 1) adults; 2) eggs;
3) rhabditiform larvae; 4)
filariform larvae; 5) free-living
female and male.
Localisation: small intestine.
Host: man
Way of transmission:
penetration of the skin by
filariform larva.
Infective stage: filariform larva

16. 16
1) within the human body:
1. Filariform larvae penetrate the skin, usually of feet
or legs in moist soil. They migrate to the lungs, enter
the alveoli, pass up the bronchi and trachea, and then
are swallowed.
2. Larvae develop into adults in the small intestine and
produce eggs.
3. The eggs develop into rhabditiform larvae that are
passed in the feces and appear in stool within 4
weeks of infection.
4. Some rhabditiform larvae develop into filariform
larvae, which penetrate the intestinal wall directly
without leaving the host and migrate to the lungs
(autoreinfection).
5. In the soil, the rhabditiform larvae develop into
filariform larvae (infective for man).
Life cycle of Strongyloides stercoralis

17. 17
2) free-living in the soil:
1. The rhabditiform larvae molt into free-living males
and females.
2. Female worms lay eggs in the soil.
3. The eggs develop into rhabditiform larvae.
4. Rhabditiform larvae develop in filariform larvae
(infective for man).
5. Clinical manifestation: 1) invasion stage: pruritis
(ground itch) at the site of larval penetration of the
skin; 2) migration stage: pneumonia, eosinophilia; 3)
intestinal stage: diarrhea, abdominal pain.
5. Laboratory diagnostics: microscopic examination
of faeces (availability of rhabditiform larvae).
6. Prevention: disposing of sewage properly and
wearing shoes.

18. 18
Life cycle of Strongyloides stercoralis

19. 19
Parasite: Trichinella spiralis
Disease: trichinosis
Distribution: Worldwide,
especially Europe, west Africa.
Morphology: 1) The adult female
worms are up to 3-4×0.6 mm;
adult male worms are up to
1.5×0.04 mm; 2) incysted larvae
(1mm) is enclosed in a fibrous
cyst wall.
Localisation: small intestine
(adult worms) and striated
muscles (larvae).
Hosts: man, pig, rat, bear, fox.
Infective stage: larva
Way of transmission: alimentary
(eating raw or undercooked meat
(usually pork), containing larvae).

20. 20
Larva of Trichinella spiralis in muscles

21. 21
1. The larvae excyst and mature into adults within the small
intestine of host.
2. Male worms die after fertilization, female worms lay larvae.
3. Larvae are released and distributed via the bloodstream to
striated muscles (diaphragm, tongue, m.deltoideus, m.pectoralis,
m.intercostalis).
4. Larvae encyst in the muscles within fibrous capcule and can
remain viable for several years.
5. Clinical manifestation: initially diarrhea, abdominal pain; by
1-2 weeks later – fever, muscle pain, periorbital edema,
eosinophilia.
6. Laboratory diagnostics: muscle biopsy reveals larvae within
striated muscle; serologic test (become positive 3 weeks after
infection).
7. Prevention: by properly cooking pork and by feeding pigs
only cooked garbage; pork inspection in slaughter houses using
a trichinoscope.
Life cycle of Trichinella spiralis

22. 22

23. 23
Pork inspection in
slaughter houses
using
a trichinoscope

24. 24
Parasite: Wuchereria
bancrofti
Common name of diseases:
Filariasis, chronic disease –
elephantiasis.
Endemic areas: Tropics
primarily
Way of transmission:
mosquito’s bite
Clinical findings: obstruction
of lymphatic vessels, causing
edema of legs and genitalia
(elephantiasis).
Diagnostics: blood smear
(microfilariae can be
demonstrated).

25. 25
Wuchereria
bancrofti causes
elephantiasis

26. 26
Life cycle of Wuchereria
bancrofti
Infective larvae are transmitted
by infected biting
mosquitoes.
The larvae migrate to
lymphatic vessels and lymph
nodes of the human host,
where they develop into
microfilariae-producing
adults.
The adults dwell in lymphatic
vessels and lymph nodes
where they can live for
several years. The female
worms produce
microfilariae which circulate
in the blood.
The microfilariae infect biting
mosquitoes. Inside the
mosquito, the microfilariae
develop in 1-2 weeks into
infective filariform (third-
stage) larvae. During a
subsequent blood meal by
the mosquito, the larvae

27. 27
Distribution of filariosis (different species)

28. 28
Parasite: Onchocerca
volvulus
Disease: Onchocerciasis
(river blindness)
Distribution: Africa, Central
America
Way of transmission:
blackfly bite
Clinical findings:
inflammation of
subcutaneous tissue,
formation of pruritic papules
and nodules; lesions of the
eyes (blindness).
Diagnostics: skin biopsy.

29. 29
Life cycle of Onchocerca volvulus

30. 30
Parasite: Loa loa – eye worm
Disease: Loiasis
Endemic areas: Tropical Africa
Way of transmission: deer fly
bite
Clinical findings: transient,
localized, nonerythematous,
subcutaneous edema (Calabar
swellings);
adult worm crawling across the
conjuctiva of the eye.
Diagnostics: blood smear
(microfilariae can be
demonstrated).

31. 31
Parasite: Dracunculus
medinensis
Disease: dracunculiasis
Endemic Areas: Tropical
Africa and Asia
Way of Transmission:
ingestion of copepods in
water.
Clinical findings:
inflammation, blistering, and
ulceration of the skin;
papule itches.
Diagnostics: clinical (by
finding the head of the worm
in the skin ulcer).

32. 32
Dracunculus medinensis
causes dracunculiasis

33. 33
Parasite: Toxocara canis –
dog roundworm
Disease: visceral larva
migrans.
Distribution: Worldwide
Host: dogs (men are not
typical hosts).
Way of transmission:
ingestion of eggs.
Clinical findings: fever,
hepatomegaly, blindness,
eosinophilia.
Diagnostics: clinical and
serologic.

34. 34
Life cycle
of
Toxocara
canis

35. 35
Thank you for attention!