MLT GlobeParasitology: Nematodes (roundworms) – page 3
66 Parasitology MCQs on Nematodes (roundworms) with answers and explanations.
A thin-shelled oval egg about 60 × 40 µm containing an early cleaving embryo (4–8 cells) and a clear space under the shell is seen in stool. It is:
Hookworm eggs are thin-shelled with a cleaving embryo. Necator and Ancylostoma eggs cannot be separated by morphology.
Guinea worm (Dracunculus medinensis) infection is acquired by:
Larvae inside water fleas (Cyclops) are swallowed in unfiltered drinking water; filtering water prevents infection.
Loa loa, the African 'eye worm', is transmitted by the bite of:
Day-biting Chrysops flies transmit Loa loa, which is why its microfilariae show daytime periodicity.
Heavy Trichuris trichiura infection in young children can cause:
Many whipworms embedded in the colonic and rectal mucosa cause dysentery-like illness and rectal prolapse in heavily infected children.
Which intestinal nematode can pass through several free-living generations in soil in addition to its parasitic cycle?
S. stercoralis has a heterogonic cycle with free-living adult males and females in soil. Hookworm larvae live in soil but do not form free-living adult generations, and Ascaris has no free-living stage.
Which intestinal helminth does NOT cause autoinfection (reinfection of the same host without an external phase)?
Ascaris eggs must embryonate in soil for weeks, so autoinfection cannot occur. H. nana, Enterobius and Strongyloides can all reinfect the same host.
For which parasite are pigs or dogs NOT a usual source of human infection?
A. lumbricoides spreads human to human via soil-contaminated eggs. Pigs transmit T. solium and Trichinella, and dogs shed Echinococcus eggs.
Which is a manifestation of acute (early) lymphatic filariasis?
Acute filarial attacks cause painful inflamed lymph nodes and vessels with fever. Elephantiasis, hydrocele and chyluria are chronic results of lymphatic obstruction.
The stage of W. bancrofti infective to humans is the third-stage (filariform) larva found in the mosquito's:
Microfilariae develop to L3 in the thoracic muscles, then move to the proboscis and enter the skin when the mosquito feeds. Larvae in the thorax are not yet infective.
Which of the following does not cause cutaneous larva migrans?
Creeping eruption results from skin migration of animal hookworm, Gnathostoma or Strongyloides larvae (larva currens). Filarial microfilariae circulate in blood and do not migrate in skin.
In bancroftian filariasis, which stage is chiefly responsible for lymphatic damage?
Adult worms and the host reaction to them (including dying adults and Wolbachia antigens) cause lymphatic dilation and blockage. Microfilariae mainly matter for transmission and diagnosis.
Which parasite is not a cause of visceral larva migrans?
Visceral larva migrans is caused by nematode larvae of animals (Toxocara, Baylisascaris) that wander through human organs. T. saginata is an intestinal tapeworm with no migrating larva in humans.
Oxyuriasis is an older name for infection with:
Enterobius was formerly placed in the genus Oxyuris, so pinworm infection was called oxyuriasis. It is now called enterobiasis.
A patient from South Asia has nocturnal cough, wheeze, very high eosinophils and high anti-filarial antibodies. This tropical pulmonary eosinophilia is linked to:
Tropical pulmonary eosinophilia is an immune reaction to microfilariae of W. bancrofti or Brugia trapped in the lungs. It responds to diethylcarbamazine.
Milky urine (chyluria) in a patient from an endemic area suggests:
Blocked lymphatics can rupture into the urinary tract, releasing chyle into urine. S. haematobium causes terminal hematuria instead.
Which helminth egg is not bile-stained (appears colorless)?
Hookworm eggs have a thin clear shell with a segmented embryo. Ascaris, Trichuris and Taenia eggs are stained yellow-brown by bile.
The dog heartworm, which occasionally causes coin lesions in human lungs, is:
D. immitis is a filarial nematode spread by mosquitoes; in humans larvae die in pulmonary arteries and form nodules. Toxocara causes larva migrans.
A stool concentrate shows larvae with a short buccal cavity and a prominent genital primordium. The patient has eosinophilia and is starting corticosteroid therapy. The organism is:
Rhabditiform larvae of Strongyloides have a short buccal canal and a visible genital primordium; hookworm larvae have a long buccal canal. Steroids can trigger fatal hyperinfection, so detection is urgent.
A child with pica and a puppy at home has eosinophilia, hepatomegaly and a retinal lesion. No eggs are found in stool. Diagnosis is best made by:
Visceral and ocular larva migrans from Toxocara do not produce eggs in human stool because larvae do not mature. Serology supports the diagnosis.
Hookworm eggs are found in a stool concentrate. How should the species be reported?
Eggs of Necator americanus and Ancylostoma duodenale cannot be told apart by microscopy, so they are reported as 'hookworm eggs'. Species identification needs adult worms, cultured larvae or molecular tests.