MCQs in Parasitology (11-20): Malaria with Answers and Explanations

Ten malaria multiple choice questions with answers and explanations, covering the Plasmodium life cycle, the differences between the species, blood-smear morphology, and clinical features. Write down your answers first, then check them against the key and explanations at the end.

Start with parasitology MCQs 1-10

11. Which is the infective form of the malaria parasite?

a. Oocyst
b. Sporozoite
c. Bradyzoite
d. Tachyzoite

12. Trophozoites, schizonts, and gametocytes of all the malarial parasites are seen in the peripheral blood smear except:

a. P. falciparum
b. P. malariae
c. P. ovale
d. P. vivax

13. Blackwater fever is a special manifestation of malaria caused by:

a. P. falciparum
b. P. malariae
c. P. ovale
d. P. vivax

14. Which Plasmodium species has the longest incubation period?

a. P. falciparum
b. P. malariae
c. P. ovale
d. P. vivax

15. Which of the following statements regarding Plasmodium falciparum are true?

a. Causes more severe disease in pregnancy
b. Is associated with recurrent relapses due to liver hypnozoites
c. Is the only malarial parasite causing greater than 20% parasitemia
d. Infection is typically associated with thrombocytopenia
e. Is the only cause of cerebral malaria

16. Mosquitoes are the vector in which of the following disorders?

a. Onchocerciasis
b. Visceral leishmaniasis
c. African trypanosomiasis
d. Bancroftian filariasis

17. Which of the following statements regarding vivax malaria are true?

a. May be complicated by anemia
b. May be complicated by jaundice
c. In a traveler, may present more than six months after exposure
d. Is sensitive to chloroquine
e. May co-exist with falciparum malaria in the same patient

18. Crescent-shaped or banana-shaped gametocytes are seen in infection with:

a. Plasmodium vivax
b. Plasmodium falciparum
c. Plasmodium ovale
d. Plasmodium malariae

19. Match each type of red-cell dot or stippling with the Plasmodium species in which it is prominently seen:

a. a-I, b-II, c-III, d-IV
b. a-II, b-I, c-IV, d-III
c. a-III, b-II, c-IV,
d-I d. a-IV, b-III, c-II, d-I

20. A situation where persistent blood-stage parasites that were never fully eliminated begin to multiply again, causing renewed clinical symptoms, is called:

a. Latency
b. Re-infection
c. Relapse
d. Recrudescence

Answer key

11. b. Sporozoite
12. a. P. falciparum
13. a. P. falciparum
14. b. P. malariae
15. a, c, and d
16. d. Bancroftian filariasis
17. a, b, c, d, and e (all)
18. b. Plasmodium falciparum
19. b. a-II, b-I, c-IV, d-III
20. d. Recrudescence

Why these are the answers

11. Sporozoite. When an infected female Anopheles mosquito takes a blood meal, it injects sporozoites from its salivary glands into the human host. These sporozoites travel through the blood to the liver and infect hepatocytes, beginning the pre-erythrocytic (liver) stage. So the sporozoite is the infective form passed from mosquito to human. Oocysts form in the mosquito, while bradyzoites and tachyzoites belong to Toxoplasma, not malaria.

12. P. falciparum. In P. falciparum infection, the maturing trophozoites and schizonts express surface proteins (such as PfEMP1) that make infected red cells stick to capillary walls deep in the organs, a process called sequestration. As a result, only the early ring forms and the crescent-shaped gametocytes are usually seen in a peripheral smear; the intermediate stages are hidden. In the other three species, all stages circulate freely and can be found peripherally.

13. P. falciparum. Blackwater fever is sudden, massive intravascular hemolysis with hemoglobinuria (the dark, cola-colored urine that names it) and a risk of acute kidney injury. It is a complication of severe P. falciparum malaria, classically linked to irregular quinine use. The milder species do not typically cause it.

14. P. malariae. P. malariae has the slowest erythrocytic cycle, taking 72 hours (quartan malaria, with fever every fourth day), and it has the longest incubation period, often 18 to 40 days or more. By contrast, P. vivax and P. ovale run 48-hour (tertian) cycles. P. malariae is also notable for causing very long-lasting, low-level infection.

15. a, c, and d. P. falciparum causes more severe disease in pregnancy (statement a is true), because of lowered immunity and heavy sequestration in the placenta. It can invade red cells of all ages, so parasitemia can exceed 20 percent, far higher than the other species (statement c is true). Thrombocytopenia is a common finding (statement d is true). The two false statements: P. falciparum does not form liver hypnozoites, so it does not cause true relapses (that is P. vivax and P. ovale), and while P. falciparum is overwhelmingly the cause of cerebral malaria, rare cerebral cases have been reported with P. vivax, so it is not the only cause.

16. Bancroftian filariasis. Lymphatic filariasis due to Wuchereria bancrofti is spread by mosquitoes (Culex, Anopheles, and Aedes). The other three have different biting-fly vectors: onchocerciasis by the blackfly (Simulium), visceral leishmaniasis by the sandfly (Phlebotomus), and African trypanosomiasis by the tsetse fly (Glossina). The trap is that all four are fly-borne, but only filariasis uses the mosquito.

17. All of them (a, b, c, d, and e). Vivax malaria can cause hemolytic anemia (a) and can affect the liver enough to cause jaundice (b). Because P. vivax forms dormant liver hypnozoites, a returning traveler can relapse and present more than six months after exposure (c). The blood-stage parasite generally remains sensitive to chloroquine (d), though radical cure of the liver stage needs a separate drug. And in endemic areas mixed infections with P. falciparum do occur in the same patient (e). All five statements are true.

18. Plasmodium falciparum. P. falciparum produces distinctive elongated, crescent-shaped (banana-shaped) gametocytes that stretch and distort the host red cell, a highly recognizable feature on a smear. The gametocytes of P. vivax, P. ovale, and P. malariae are round or oval, not crescentic. Seeing banana-shaped gametocytes is essentially diagnostic of P. falciparum.

19. a-II, b-I, c-IV, d-III. The red-cell dots and stipplings each point to a species: Maurer's clefts (coarse, comma-shaped) to P. falciparum; Schüffner's dots (fine, brick-red) to P. vivax; Ziemann's stippling (fine and faint, needing prolonged staining) to P. malariae; and James' dots to P. ovale. One precise point worth knowing: Schüffner's-type stippling actually appears in both P. vivax and P. ovale, and James' dots are essentially the P. ovale form of that stippling. For exam purposes the signature pairing is Schüffner's with vivax and James' with ovale, which gives the match a-II, b-I, c-IV, d-III.

20. Recrudescence. Recrudescence is the return of symptoms from blood-stage parasites that fell below detectable levels but were never fully cleared, then multiplied again. It is important to separate this from relapse, which is renewed infection from dormant liver hypnozoites and therefore happens only with P. vivax and P. ovale. Re-infection means a fresh mosquito bite, and latency refers to the dormant period itself. The key distinction: recrudescence comes from surviving blood-stage parasites, relapse from the liver.