MLT GlobeParasitology: Nematodes (roundworms) – page 2
66 Parasitology MCQs on Nematodes (roundworms) with answers and explanations.
A patient with fever, periorbital edema, muscle pain and high eosinophils ate undercooked pork. A muscle biopsy is ordered to look for:
Trichinella larvae encyst in striated muscle and can be seen in compressed or stained biopsy tissue. The other worms are intestinal and diagnosed by stool examination.
To detect Wuchereria bancrofti microfilariae in most endemic regions, blood should be collected:
Most W. bancrofti strains show nocturnal periodicity, peaking in blood at night when Culex vectors bite. Loa loa has diurnal periodicity.
The Knott concentration method (2% formalin) on venous blood is used to detect:
Knott's technique lyses red cells and concentrates microfilariae in the sediment, improving sensitivity in low-density filarial infection. Malaria is diagnosed by thick and thin films.
Which nematode lives in human tissues rather than the intestine?
The Guinea worm, D. medinensis, lives in subcutaneous tissue and emerges through a skin blister. The other three are intestinal nematodes.
The female Culex mosquito is an important vector of:
Culex quinquefasciatus is the main urban vector of W. bancrofti. Malaria is transmitted by Anopheles; ascariasis and amoebiasis are fecal-oral.
Which worm can reinfect the same person by transfer of eggs from the perianal skin to the mouth?
Scratching the itchy perianal area moves pinworm eggs to fingers and mouth, causing autoinfection. Ascaris and hookworm need soil development, and Trichinella needs a new host.
What is the usual diagnostic stage of Ascaris lumbricoides in stool?
Eggs with a thick mammillated coat are shed in large numbers and identified on wet mount. Cysts and trophozoites are protozoan stages.
Which statement about the life cycle of Enterobius vermicularis is correct?
The pinworm has a direct life cycle: eggs become infective within hours on the perianal skin and are swallowed. No vector or second host is involved.
Humans acquire Ascaris lumbricoides by swallowing:
Eggs become infective after about 2 to 3 weeks in soil when a larva develops inside. Filariform skin penetration is typical of hookworm and Strongyloides.
A colorless, oval egg flattened on one side, with a larva inside, is found on a tape preparation. It belongs to:
Pinworm eggs are plano-convex (D-shaped), thin-shelled and often contain a larva. Trichuris eggs are barrel-shaped with polar plugs, and Ascaris eggs are mammillated.
River blindness is another name for:
Onchocerca volvulus, spread by Simulium blackflies breeding near rivers, damages the eye. Loiasis is eye worm disease without blindness.
Which finding is characteristic of onchocerciasis?
Adult O. volvulus lie coiled in fibrous skin nodules (onchocercomata) over bony areas. Microfilariae cause itchy dermatitis and eye lesions.
Which specimen is used to find microfilariae of Onchocerca volvulus?
Onchocerca microfilariae live in the skin, not the blood, so bloodless skin snips are incubated in saline and examined. Blood films are used for Wuchereria and Loa loa.
Which helminth infects the largest number of people worldwide?
Ascaris is the most common soil-transmitted helminth, infecting several hundred million people. Trichinella and Strongyloides are far less common.
Which of these parasites completes its life cycle in a single host with no intermediate host?
Ascaris is transmitted directly by eggs matured in soil. Taenia needs pigs, Plasmodium needs mosquitoes and Fasciola needs snails.
The normal habitat of adult Ascaris lumbricoides is the:
Adults live free in the lumen of the jejunum and ileum. They may migrate to the appendix or bile duct, but this is abnormal.
Elephantiasis of the legs or scrotum is most often caused by:
W. bancrofti (and Brugia species) cause lymphatic filariasis, leading to chronic lymphedema. The others are intestinal or hepatic helminths.
In Ascaris, the male can be distinguished from the female by its curved tail. Differences in form between sexes are called:
Many nematodes show sexual dimorphism: males are smaller with a curved posterior end. Hermaphroditism means both sexes in one individual, as in most tapeworms.
For suspected Loa loa infection, blood for microfilariae should be collected:
Loa loa shows diurnal periodicity, with peak numbers between about 10:00 and 14:00. Nocturnal collection is used for Wuchereria and Brugia.
A round-to-oval egg about 60 µm with a thick, bumpy (mammillated) outer layer is seen in stool. It is:
Fertile Ascaris eggs have a thick mammillated coat and are often bile-stained brown. Trichuris eggs are barrel-shaped with polar plugs.