MLT GlobeParasitology: Blood & tissue protozoa – page 5
108 Parasitology MCQs on Blood & tissue protozoa with answers and explanations.
In a routine peripheral smear, schizonts are usually absent and only rings and gametocytes are seen in infection with:
Mature P. falciparum stages sequester in deep capillaries, so blood films show mainly rings and banana-shaped gametocytes. Schizonts in the film suggest very heavy, severe infection.
The spleen enlarges in kala-azar mainly because of:
Leishmania donovani multiplies in macrophages, causing marked proliferation of the reticuloendothelial cells in the spleen, liver and marrow. Portal hypertension is the mechanism in schistosomiasis.
Blackwater fever in falciparum malaria results from:
Sudden widespread intravascular hemolysis releases free hemoglobin that is filtered into urine, making it dark. Capillary blockage underlies cerebral malaria, not blackwater fever.
In a Leishmania promastigote, the free flagellum arises from which part of the cell?
Promastigotes are elongated with the kinetoplast and basal body near the front, and a free flagellum projects from the anterior end. Amastigotes lack a free flagellum.
A wet, rapidly ulcerating skin sore (rural cutaneous leishmaniasis) is mainly caused by:
L. major, with a rodent reservoir, causes the wet rural type of Old World cutaneous leishmaniasis. L. tropica causes the dry urban type, and L. donovani is visceral.
The main reservoir hosts of Leishmania major are:
L. major is a zoonosis maintained in desert rodents like gerbils. Dogs are the main reservoir for L. infantum (visceral leishmaniasis).
Which protozoan has no flagella, cilia or pseudopodia and moves by gliding?
Apicomplexans such as Toxoplasma lack locomotory organelles and use gliding motility. Amoebae use pseudopodia, while Giardia and Trichomonas have flagella.
Leishmania donovani survives the host's immune response mainly by:
Amastigotes live inside macrophage phagolysosomes, inhibiting oxidative burst and antigen presentation. This lets them multiply in the cells meant to destroy them.
Before transmission, Leishmania promastigotes in the sandfly mature into which infective form?
Procyclic promastigotes multiply in the midgut and then become non-dividing metacyclic promastigotes, which are injected during feeding. Amastigotes form only after entering host cells.
Which sign is not typical of human babesiosis?
Babesia infects red cells, causing hemolysis with anemia, jaundice and dark urine. Lymph node enlargement is not a feature.
To check for CNS involvement (stage 2) in African trypanosomiasis, which specimen is examined?
CSF is tested for trypanosomes and raised white cells to stage the disease, which guides treatment choice. Blood and lymph node aspirates detect early infection.
Crescent-shaped tachyzoites that multiply inside nucleated host cells by endodyogeny are characteristic of:
Toxoplasma tachyzoites are arc-shaped and divide by internal budding within many cell types. P. falciparum gametocytes are crescent-shaped but do not multiply, and Plasmodium reproduces by schizogony.
A patient returned from a tick-infested area of the northeastern USA with fever and hemolysis. The smear shows small rings, some in tetrads ('Maltese cross'), with no pigment. The most likely organism is:
Babesia forms tetrads and lacks hemozoin pigment and gametocytes, and is transmitted by Ixodes ticks. P. falciparum shows small rings too but has banana-shaped gametocytes and no tetrads.
Infected red cells are enlarged and contain fine pink-red stippling (Schüffner dots) with amoeboid trophozoites. The most likely species is:
P. vivax prefers reticulocytes, so infected cells are enlarged, and they show Schüffner dots. P. malariae infects older cells, which stay normal-sized, and forms band trophozoites.
A thin blood film shows normal-sized red cells containing band-shaped trophozoites across the cell and a schizont with 8 merozoites arranged in a rosette around pigment. The species is:
Band forms and rosette schizonts with about 8 merozoites in normal or small red cells suggest P. malariae. P. vivax enlarges red cells and has 12–24 merozoites.
A traveller from Malaysian Borneo has daily fevers and high parasitemia. Early forms look like P. falciparum and later forms look like P. malariae band forms. The most likely species is:
P. knowlesi, a zoonotic macaque malaria in Southeast Asia, has a 24-hour cycle, can reach high parasitemia, and mimics P. falciparum rings and P. malariae bands. PCR confirms it.
A splenectomised patient from the north-eastern USA has intraerythrocytic ring forms with no pigment, extracellular forms, and occasional tetrads ('Maltese cross'). The likely organism is:
Babesia rings lack haemozoin pigment and schizonts, may be extracellular, and tetrads are diagnostic. Plasmodium produces pigment and schizonts.
A thick film from a patient in Central America shows a trypomastigote with a large posterior kinetoplast, often curved into a 'C' shape. The organism is:
T. cruzi trypomastigotes have a large kinetoplast and a typical C shape; it causes Chagas disease in the Americas. African trypanosomes have a small kinetoplast.
A bone marrow aspirate shows small oval organisms inside macrophages, each with a nucleus and a rod-shaped kinetoplast. The patient has fever, weight loss and splenomegaly. The diagnosis is:
Leishmania amastigotes are identified by a nucleus plus a bar-shaped kinetoplast. Histoplasma yeasts look similar but have no kinetoplast.
A traveller returns from a safari in East Africa with a painful skin chancre, high fever and enlarged lymph nodes. A thin blood film shows slender flagellates with an undulating membrane and a small subterminal kinetoplast. The organism is:
East African sleeping sickness (T. b. rhodesiense) produces many trypomastigotes in blood, with a small kinetoplast. T. cruzi has a large kinetoplast and a C-shaped form and occurs in the Americas.