MLT GlobeParasitology: Blood & tissue protozoa
108 Parasitology MCQs on Blood & tissue protozoa with answers and explanations.
Which parasite is identified within red cells on a Giemsa-stained blood film?
Plasmodium species infect erythrocytes, appearing as rings, trophozoites, schizonts or gametocytes. The other protozoa live in the intestine or urogenital tract.
A traveler returns with fever. Which test is the laboratory gold standard for diagnosing and speciating malaria?
Thick films detect parasites sensitively, while thin films allow species identification and parasitemia counts. Widal is for typhoid; malaria is not diagnosed from stool or urine.
A pregnant woman is advised to avoid cleaning a litter tray to reduce the risk of:
Cats are the definitive host of Toxoplasma gondii and shed oocysts in faeces. Congenital infection can damage the fetus.
A pregnant woman acquires a primary protozoan infection from undercooked meat, and her newborn develops chorioretinitis and intracranial calcifications. Which parasite was transmitted across the placenta?
Toxoplasma gondii tachyzoites cross the placenta during acute maternal infection, causing congenital toxoplasmosis. The other parasites are acquired by ingesting cysts or eggs and are not transmitted vertically.
On a thin film, infected red cells are enlarged to about 1.5–2 times normal and contain irregular amoeboid trophozoites. Which Plasmodium species is most likely?
P. vivax prefers reticulocytes, which it enlarges markedly, and has amoeboid trophozoites. P. falciparum, P. malariae and P. knowlesi leave the red cell normal-sized or smaller.
In the malaria life cycle, which insect acts as the definitive host because sexual reproduction of Plasmodium occurs in it?
Only female Anopheles mosquitoes take blood meals, ingest gametocytes and support fertilisation and sporogony, making them the definitive host. Males feed on plant juices; Culex and Aedes do not transmit human malaria.
Which Plasmodium species is responsible for most severe, potentially fatal ('malignant tertian') malaria with cerebral involvement?
P. falciparum causes high parasitaemia and cytoadherence of infected red cells in microvessels, leading to cerebral malaria and death. The other species usually cause benign malaria, although severe vivax does occur.
A fin-like undulating membrane running along the body, with a free anterior flagellum, is characteristic of the trypomastigote of which genus?
Trypanosome trypomastigotes have a flagellum attached to the body by an undulating membrane. Leishmania amastigotes lack an external flagellum, Plasmodium has none, and Giardia has four pairs of free flagella.
Novy–MacNeal–Nicolle (NNN) biphasic medium is used to culture which parasite?
On NNN medium Leishmania amastigotes transform into motile promastigotes. Trichomonas is grown in Diamond's/InPouch media, Entamoeba in xenic media, and Cryptococcus is a yeast grown on fungal media.
Which Plasmodium stage does the female Anopheles mosquito inject into human skin during a blood meal?
Sporozoites from the mosquito salivary glands are inoculated and travel to the liver. Merozoites are released from schizonts in humans, gametocytes are taken up by the mosquito, and hypnozoites are dormant liver forms.
Chagas disease (American trypanosomiasis) is caused by:
T. cruzi causes Chagas disease, transmitted by triatomine bugs. T. b. gambiense causes African sleeping sickness and L. donovani causes kala-azar.
A thin blood film shows banana-shaped (crescentic) gametocytes. Which species is present?
Crescent-shaped gametocytes are diagnostic of P. falciparum. The gametocytes of the other species are round or oval.
Which Leishmania form, injected by the sandfly, initiates human infection?
Flagellated metacyclic promastigotes are inoculated by the sandfly and become amastigotes inside macrophages. Trypo- and epimastigotes are trypanosome stages.
Which statement about human malaria is INCORRECT?
Gametocytes develop inside red blood cells in the circulation, not in the gut. The other statements correctly describe the cycle.
Members of the phylum Apicomplexa such as Plasmodium and Toxoplasma reproduce by:
Apicomplexans alternate asexual schizogony with sexual gametogony and sporogony, often in different hosts.
Brown-black pigment granules seen in malaria-infected red cells and in monocytes are hemozoin. What is hemozoin?
Plasmodium digests haemoglobin and polymerises the toxic haem into insoluble hemozoin (malaria pigment). Schistosomes make a similar pigment, but the term classically refers to malaria.
Which of the following is NOT a haemoflagellate?
Plasmodium knowlesi is an apicomplexan malaria parasite with no flagellum. The trypanosomes are flagellated blood parasites.
A patient from Bihar has fever, massive splenomegaly and pancytopenia; a bone marrow smear shows amastigotes. Which species causes this visceral disease?
Visceral leishmaniasis (kala-azar) in South Asia and East Africa is caused by L. donovani. L. tropica causes cutaneous and L. braziliensis mucocutaneous disease.
Old World cutaneous leishmaniasis ('oriental sore', Baghdad boil) is classically caused by:
L. tropica (and L. major) cause cutaneous 'oriental sore'. L. donovani is visceral and L. braziliensis is New World mucocutaneous.
West African (chronic) sleeping sickness is caused by:
T. b. gambiense causes chronic West/Central African trypanosomiasis, spread by tsetse flies. T. cruzi causes Chagas disease; Leishmania are sandfly-borne.