Theme: Medical helminthology: Roundworms – human parasites   Lecturer: ass. prof. Tetyana Bihunyak

The main questions: 1. General characteristic of class Nematoda. 2.  Intestinal Nematodes: 2.1. Ascaris lumbricoides. 2.2. Enterobius vermicularis (Pinworm). 2.3. Trichuris trichiura (Whipworm). 2.4. Hookworms: Ancylostoma duodenale, Necator americanus. 2.5. Strongyloides stercoralis (Threadworm). 2.6. Trichinella spiralis. 3. Tissue Nematodes: 3.1. Dracunculus medinensis. 3.2. Wuchereria bancrofti. 3.3. Onchocerca volvulus. 3.4. Toxocara canis. 3.5. Loa loa.

2. Cylindrical, round in cross sections (Roundworms). Class Nematoda (Roundworms): 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: 1)    Outer laminated non-cellular cuticle. 2)    Subcuticular epithelium (hypodermis); 3)Muscle layer (4 groups of longitudinal cords).

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. 9.1. Male reproductive organs: testis (long convoluted tube), vas deferens, seminal vesicle, ejaculatory duct (opens to cloaca). 9.2.Female reproductive organs: two ovaries (convoluted tubes), oviducts, uteri, vagina, vulva.

Parasite: Ascaris lumbricoides Disease: ascariasis Geographical distribution: cosmopolitan 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 Mode of transmission: fecal-oral (alimentary). Infective stage: eggs. Localisation: small intestine (adult), liver, lungs, heart (larvae).

Female Male Ascaris lumbricoides

Egg Ascaris lumbricoides

Life cycle of Ascaris lumbricoides 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 vegetables, hands. 4. Eggs hatch in the small intestine. 5. 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. 6. Within the small intestine, larvae become adult worms. Eggs appear in feces about 2 months after infection.

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 diagnosis: microscopic examination of feces (availability of eggs); larvae may be found in sputum. Prophylaxis: washing hands before meals; proper washing of vegetables eaten raw; treatment of patients; health education.

Ascaris lumbricoides

Parasite: Enterobius vermicularis Disease: enterobiasis Geographical distribution: cosmopolitan 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, with thin and smooth membrane, 40-60 micro;m. Host: man. Mode of transmission: fecal-oral (alimentary). Infective stage: eggs. Localisation: large intestine (caecum).

Enterobius vermicularis Male Female Enterobius vermicularis

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. Clinical manifestation: Infection is frequent among children. Perianal pruritus (itching) is most common symptom. Laboratory diagnosis: the eggs are recovered from perianal skin by using the “Scotch tape” technique and can be microscopically. Prophylaxis: keep sanitary condition, dehelminthization of the population.

Disease: trichocephaliasis (whipworm infection) Parasite: Trichuris trichiura Disease: trichocephaliasis (whipworm infection) Geographical distribution: cosmopolitan 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 micro;m in size. Host: man. Mode of transmission: fecal-oral (alimentary). Infective stage: eggs. Localisation: caecum, appendix, first 1/3 part of large intestine.

Trichuris trichiura

Egg

Life cycle of Trichuris trichiura: 1. Immature eggs pass in the feces (2,000 eggs/day). 2. Under favourable environmental conditions (temperature 26-28 C, oxygen, humidity 80-90%) larvae develop inside the eggs 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. 5. Eggs appear in feces about 2 months after infection. Pathogenesis and 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 diagnosis: microscopic examination of feces (availability of eggs). Prophylaxis: washing hands before meals; proper washing of vegetables eaten raw; treatment of patients; health education.

Parasites: Ancylostoma duodenale, Necator americanus Disease: ancylostomiasis Morphology: 1) Adult worms about 1 cm in length; 2) Eggs are translucent, oval with blunt poles, 40-60 micro;m in size; 3) the rhabditiform larva is about 0.25-0.5 micro;m with rhabditiform oesophagus (1/3 body length), pointed tail end; 4) the filariform larva is about 0.6-0.7 micro;m with cylindrical oesophagus (1/4 body length), sharply pointed tail. Host: man. Mode of transmission: penetration of skin by filariform larva Infective stage: filariform larva.

of Ancylostoma duodenale Buccal capsule of Ancylostoma duodenale

Life cycle of Ancylostoma and Necator: 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. 3. They develop into adults in the small intestine, attaching to the wall with either cutting plates (Necator) or teeth (Ancylostoma). They feed blood. 4. Immature eggs pass in the feces about 2 months after infection. 5.Under favourable environmental conditions in the soil eggs develop into rhabditiform larva and then into filariform larvae. (infective stage). Clinical manifestation: 1) invasion stage: dermatitis and itching (“ground itch”); 2) migration stage: pneumonia, eosinophilia; 3) intestinal stage: anemia, diarrhea, abdominal pain, nausea. Laboratory diagnosis: microscopic examination of feces (availability of eggs). Blood in the stool is frequent. Prophylaxis: disposing of sewage properly and wearing shoes.

Parasites: Strongyloides stercoralis Disease: strongyloidiasis Geographical distribution: cosmopolitan Morphology: 1) adults; 2) eggs; 3) rhabditiform larvae; 4) filariform larvae; 5) free-living female and male. Localisation: small intestine. Host: man. Mode of transmission: penetration of the skin by filariform larva. Infective stage: filariform larva.

Life cycle of Strongyloides stercoralis 1) within the human body: 1.  Filariform larvae penetrate the skin, usually of feet or legs in moist soil. 2.  They migrate to the lungs, enter the alveoli, pass up the bronchi and trachea, and then are swallowed. 3.   Larvae develop into adults in the small intestine and produce eggs. 4.   The eggs form rhabditiform larvae that are passed in the feces and appear in stool within 4 weeks of infection. 5.    Some rhabditiform larvae form filariform larvae, which penetrate the intestinal wall directly without leaving the host and migrate to the lungs (autoreinfection). 6.    In the soil, the rhabditiform larvae develop into filariform larvae (infective for man).

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; rhabditiform larvae form filariform larvae (infective for man). 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. Laboratory diagnosis: microscopic examination of faeces (availability of rhabditiform larvae). Prophylaxis: disposing of sewage properly and wearing shoes.

Parasites: Trichinella spiralis Disease: trichinosis Geographical distribution: especially Europe, west Africa Morphology: 1) The adult female worms are up to 3-4  0.6 mm; the adult male worms are up to 1.5  0.04 mm; 2) the incysted larvae (1 mm) 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 Mode of transmission: alimentary (eating raw or undercooked meat (usually pork), containing larvae.

Larva of Trichinella spiralis

Life cycle of Trichinella spiralis: 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. Clinical manifestation: initially diarrhea, abdominal pain; by 1-2 weeks later – fever, muscle pain, periorbital edema, eosinophilia. Laboratory diagnosis: muscle biopsy reveals larvae within striated muscle; serologic test (become positive 3 weeks after infection). Prophylaxis: by properly cooking pork and by feeding pigs only cooked garbage; pork inspection in slaughter houses using a trichinoscope.

Pork inspection in slaughter houses using a trichinoscope.

Species: Wuchereria bancrofti Common Name of Disease: Filariasis Endemic Areas: Tropics primarily Mode of Transmission: Mosquito bite Clinical Findings: Obstruction of lymphatic vessels, causing edema of legs and genitalia (elephantiasis). Diagnosis: Blood smear (microfilariae can be demonstrated).

Wuchereria bancrofti causes elephantiasis

Wuchereria bancrofti causes edema of leg and genitalia

Species: Onchocerca volvulus Common Name of Disease: Onchocerciasis (river blindness) Endemic Areas: Africa, Central America Mode of Transmission: Blackfly bite Clinical Findings: Inflammation of subcutaneous tissue, formation of pruritic papules and nodules; lesions of the eyes (blindness). Diagnosis: Skin biopsy.

Species: Loa loa Common Name of Disease: Loiasis Endemic Areas: Tropical Africa Mode of Transmission: Deer fly bite Clinical Findings: Transient, localized, nonerythematous, subcutaneous edema (Calabar swellings); adult worm crawling across the conjuctiva of the eye. Diagnosis: Blood smear (microfilariae can be demonstrated).

Species: Dracunculus medinensis Common Name of Disease: Dracunculiasis Endemic Areas: Tropical Africa and Asia Mode of Transmission: Ingestion of copepods in water Clinical Findings: Inflammation, blistering, and ulceration of the skin; papule itches. Diagnosis: Clinical (by finding the head of the worm in the skin ulcer).

Dracunculus medinensis causes dracunculiasis

Species: Toxocara canis Common Name of Disease: Visceral larva migrans Endemic Areas: Woldwide Mode of Transmission: Ingestion of eggs Clinical Findings: Fever, hepatomegaly, blindness, eosinophilia. Diagnosis: Clinical and serologic.

Life cycle of Toxocara canis

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