MCQs Parasitology (1-10) with Answers and Explanations

Ten parasitology multiple choice questions with answers and explanations, covering the major helminths and protozoa, how they are transmitted, and how they are diagnosed. Write down your answers first, then check them against the key and explanations at the end.

1. Each of the following statements concerning Ascaris lumbricoides is correct except:
a. Ascaris lumbricoides is one of the largest nematodes
b. Ascaris lumbricoides can cause pneumonia
c. Both dogs and cats are intermediate hosts of Ascaris lumbricoides
d. A. lumbricoides is transmitted by ingestion of eggs

2. Each of the following statements concerning kala-azar is correct except:

a. Kala-azar is caused by Leishmania donovani
b. Kala-azar is transmitted by the bite of sandflies
c. Kala-azar occurs primarily in rural Latin America
d. Kala-azar can be diagnosed by finding amastigotes in bone marrow

3. Each of the following statements concerning hookworm infection is correct except:

a. Hookworm infection can cause pneumonia
b. Hookworm infection is acquired when filariform larvae penetrate the skin
c. Hookworm infection is caused by Necator americanus
d. Hookworm infection can be diagnosed by finding the trophozoite in the stool

4. Each of the following statements concerning Trichomonas vaginalis is correct except:

a. T. vaginalis is transmitted sexually
b. T. vaginalis can be diagnosed by visualizing the trophozoite
c. T. vaginalis can be treated effectively with metronidazole
d. T. vaginalis causes bloody diarrhea

5. Each of the following statements concerning Giardia lamblia is correct except:

a. G. lamblia has both a trophozoite and a cyst stage in its life cycle
b. G. lamblia is transmitted by the fecal-oral route from both human and animal sources
c. G. lamblia causes hemolytic anemia
d. G. lamblia can be diagnosed by the string test

6. Each of the following statements concerning malaria is correct except:

a. The female Anopheles mosquito is the vector
b. In early infection, sporozoites enter hepatocytes
c. Release of merozoites from red blood cells causes fever and chills
d. The principal site of gametocyte formation is the human gastrointestinal tract

7. Each of the following parasites is transmitted by mosquitoes except:

a. Leishmania donovani
b. Wuchereria bancrofti
c. Plasmodium vivax
d. Plasmodium falciparum

8. Pigs or dogs are the source of human infection by each of the following parasites except:

a. Echinococcus granulosus
b. Taenia solium
c. Ascaris lumbricoides
d. Trichinella spiralis

9. In malaria, the form of plasmodia transmitted from mosquito to human is the:

a. Sporozoite
b. Gametocyte
c. Merozoite
d. Hypnozoite

10. Which of the following is used to prevent malaria?

a. Mebendazole
b. Chloroquine
c. Inactivated whole-cell vaccine
d. Zinc tablet

Continue with MCQs in Parasitology 11-20 focused mainly on (Malaria).

Answer key

1. c. Both dogs and cats are intermediate hosts of Ascaris lumbricoides
2. c. Kala-azar occurs primarily in rural Latin America
3. d. Hookworm infection can be diagnosed by finding the trophozoite in the stool
4. d. T. vaginalis causes bloody diarrhea
5. c. G. lamblia causes hemolytic anemia
6. d. The principal site of gametocyte formation is the human gastrointestinal tract
7. a. Leishmania donovani
8. c. Ascaris lumbricoides
9. a. Sporozoite
10. b. Chloroquine

Why these are the answers

1. Both dogs and cats are intermediate hosts of Ascaris lumbricoides. This is the false statement, so it is the answer. Ascaris has no intermediate host at all; humans are the only host, and infection spreads directly when eggs from human feces contaminate food or soil and are swallowed. The true statements are that it is one of the largest intestinal nematodes, that its migrating larvae can pass through the lungs and cause a pneumonia-like illness (Loffler syndrome), and that it is transmitted by ingesting eggs.

2. Kala-azar occurs primarily in rural Latin America. This is false, so it is the answer. Kala-azar (visceral leishmaniasis) is concentrated in South Asia (the Indian subcontinent), East Africa, and parts of the Middle East, not primarily Latin America. The true statements are that it is caused by Leishmania donovani, transmitted by the bite of sandflies, and diagnosed by finding amastigotes (Leishman-Donovan bodies) in bone marrow or splenic aspirate.

3. Hookworm infection can be diagnosed by finding the trophozoite in the stool. This is false, so it is the answer. Hookworms are helminths (worms), and worms do not have a trophozoite stage; that term belongs to protozoa such as Giardia. Hookworm is diagnosed by finding its characteristic eggs in the stool. The true statements are that migrating larvae can cause pulmonary symptoms, that infection is acquired when filariform larvae penetrate the skin (classically of the feet), and that Necator americanus is a cause.

4. T. vaginalis causes bloody diarrhea. This is false, so it is the answer. Trichomonas vaginalis infects the genital tract, not the gut: it causes vaginitis with a frothy discharge in women and is often asymptomatic in men. The true statements are that it is sexually transmitted, diagnosed by seeing the motile trophozoite (it has no cyst stage), and treated with metronidazole.

5. G. lamblia causes hemolytic anemia. This is false, so it is the answer. Giardia lives in the small intestine and interferes with fat and nutrient absorption, causing greasy, foul diarrhea and malabsorption, not hemolytic anemia. The true statements are that it has both trophozoite and cyst stages, spreads by the fecal-oral route from human and animal sources, and can be sampled from the duodenum by the string test (Enterotest).

6. The principal site of gametocyte formation is the human gastrointestinal tract. This is false, so it is the answer. Gametocytes form inside red blood cells in the human bloodstream, not the gastrointestinal tract, and the sexual stages then complete their development in the mosquito's gut after a blood meal. The true statements describe the rest of the cycle correctly: the female Anopheles is the vector, sporozoites first infect liver cells (hepatocytes), and the synchronized rupture of red cells releasing merozoites produces the fever-and-chills paroxysms of malaria.

7. Leishmania donovani. The question asks which parasite is not mosquito-transmitted. Leishmania donovani is transmitted by sandflies, not mosquitoes, so it is the exception. The others are all mosquito-borne: Wuchereria bancrofti (lymphatic filariasis) by Culex and other mosquitoes, and Plasmodium vivax and Plasmodium falciparum (malaria) by Anopheles. The trap is that sandflies and mosquitoes are both biting flies, but they are different vectors.

8. Ascaris lumbricoides. The question asks which parasite is not acquired from pigs or dogs. Ascaris is acquired by swallowing eggs from human-feces-contaminated soil, with no pig or dog involvement, so it is the exception. The others all involve those animals: Echinococcus granulosus uses dogs as the definitive host (humans get hydatid disease from dog feces), while Taenia solium (pork tapeworm) and Trichinella spiralis (trichinosis) are both acquired from eating undercooked pork.

9. Sporozoite. When an infected Anopheles mosquito bites, it injects sporozoites from its salivary glands into the human, and these travel to the liver to begin the infection. So the sporozoite is the form passed from mosquito to human. The other forms belong to different points in the cycle: merozoites and gametocytes develop in the human, and hypnozoites are the dormant liver stage of P. vivax and P. ovale.

10. Chloroquine. Of the options given, chloroquine is the antimalarial: it has long been used both to treat and to prevent malaria. Two important caveats belong with this answer. First, chloroquine resistance is now widespread in Plasmodium falciparum, so the drug chosen for prevention depends on the region and its resistance pattern; chloroquine is no longer universally effective. Second, prevention is no longer limited to drugs: the WHO now recommends two malaria vaccines for children in endemic areas, RTS,S/AS01 and R21/Matrix-M (these are recombinant subunit vaccines, not the "inactivated whole-cell vaccine" in option c, which does not exist for malaria). Mebendazole is an anthelmintic (for worms, not malaria), and a zinc tablet has no antimalarial role.