MLT GlobeParasitology: Blood & tissue protozoa – page 3
108 Parasitology MCQs on Blood & tissue protozoa with answers and explanations.
The promastigote form of Leishmania is normally found in:
Promastigotes develop in the sandfly midgut and in culture. Inside the human host, the parasite lives as amastigotes.
Which of these is an obligate intracellular parasite?
Toxoplasma multiplies only inside nucleated host cells. The other three live extracellularly in the gut or genital tract.
In the life cycle of Toxoplasma gondii, humans act as:
Humans harbor tachyzoites and tissue cysts only; the sexual cycle and oocyst shedding occur in cats (the definitive host).
In African trypanosomiasis, which form is looked for in blood, lymph node aspirate or CSF?
T. brucei exists in humans only as extracellular trypomastigotes with an undulating membrane. Promastigotes belong to Leishmania in the vector or culture.
Flagellated protozoa that live in human blood and tissues, such as Trypanosoma and Leishmania, are called:
Hemoflagellates are kinetoplastid flagellates of blood and tissue. Sporozoa (Apicomplexa) include Plasmodium, which has no flagella in human stages.
After an infected Anopheles bite, where do Plasmodium sporozoites first go to multiply in the human body?
Sporozoites travel to the liver and undergo exo-erythrocytic schizogony in hepatocytes. Only the merozoites released from the liver invade red cells.
A thin blood film shows many small ring forms, some with two chromatin dots, in normal-sized red cells, plus crescent (banana)-shaped gametocytes. The species is:
P. falciparum shows multiple small rings, double chromatin dots and appliqué forms in unenlarged cells; its gametocytes are crescent shaped. Mature stages are usually absent from the blood.
Crescent- or banana-shaped gametocytes on a thin blood film are characteristic of:
P. falciparum gametocytes are crescent-shaped, while the other species have round gametocytes. P. vivax shows enlarged cells with Schüffner dots instead.
A young man develops rapidly fatal meningoencephalitis a few days after swimming in a warm freshwater lake. Motile amoebae are seen in a wet mount of CSF. The organism is:
Primary amoebic meningoencephalitis from Naegleria follows freshwater exposure through the nose. CSF should be examined warm and not refrigerated. Acanthamoeba causes slower granulomatous encephalitis or keratitis.
Trypanosoma cruzi, the cause of Chagas disease, is transmitted by:
Infective trypomastigotes are passed in the bug's faeces and enter through the bite wound or mucous membranes.
African sleeping sickness (Trypanosoma brucei) is transmitted by the bite of the:
Tsetse flies transmit T. brucei gambiense and rhodesiense; sandflies transmit Leishmania.
Which inherited red cell condition gives partial protection against severe falciparum malaria?
Red cells of HbAS carriers sickle and are removed when parasitised, reducing the risk of severe falciparum malaria.
Two weeks after eating undercooked hamburger, a patient has lethargy, fatigue and tender lymph nodes; heterophil test is negative. Which organism is most likely?
Tissue cysts in undercooked meat transmit toxoplasmosis, causing a mononucleosis-like illness after 1-3 weeks. The bacteria listed cause acute gastroenteritis within hours to days.
When should a blood film be collected from a patient with suspected malaria, according to current guidance?
WHO/CDC advise sampling as soon as malaria is suspected, before treatment and regardless of fever timing; if negative, films are repeated (usually every 12–24 h, three sets). Waiting for a paroxysm delays diagnosis.
In Trypanosoma and Leishmania, the 'kinetoplast' seen near the base of the flagellum is:
The kinetoplast is a DNA-rich region of the single large mitochondrion, lying next to the basal body. It stains dark with Giemsa and helps identify amastigotes.
In the human host, Plasmodium multiplies asexually in liver cells and red blood cells by which process?
Schizogony (multiple nuclear division producing merozoites) occurs in hepatocytes and RBCs. Sporogony is the sexual-phase multiplication in the mosquito.
In current classification, malaria parasites belong to which phylum?
Plasmodium, with Toxoplasma and Cryptosporidium, belongs to the Apicomplexa (older term: Sporozoa), named for the apical complex used to invade cells. Platyhelminthes are flatworms.
On a thin film, ring forms sit flattened against the edge of the red cell ('appliqué' or accolé forms). This is typical of:
Accolé forms, along with multiple rings per cell and double chromatin dots, are characteristic of P. falciparum.
Coarse, irregular red-staining clefts (Maurer's clefts) in red cells containing mature trophozoites are associated with:
Maurer's clefts are membrane structures made by P. falciparum. Vivax and ovale show fine Schüffner's dots, and malariae shows Ziemann's dots.
Fine, uniform red stippling (Schüffner's dots) in enlarged infected red cells is a feature of which species?
Schüffner's (James's) dots appear in RBCs infected by P. vivax and P. ovale. P. falciparum shows Maurer's clefts and P. malariae Ziemann's dots.