A 30-year-old woman has a frothy, yellow-green vaginal discharge. Why should the saline wet mount for Trichomonas vaginalis be examined within minutes of collection?

The trophozoites stop moving as they cool

Vaginal lactobacilli lyse the trophozoites

The trophozoites turn into cysts outside the body

Clue cells soon hide the trophozoites

In the Sabin-Feldman dye test for toxoplasmosis, a serum containing specific antibody is shown by live tachyzoites that:

Fail to take up alkaline methylene blue

Stain deep blue with methylene blue

Clump together in visible agglutinates

Turn green under ultraviolet light

Two weeks after a blood transfusion in Kochi, a 60-year-old woman who has never left Kerala develops fever. Her thin film shows P. vivax with Schüffner's dots, and she is cured with chloroquine. Why is primaquine not needed for her?

Transfused blood carries no sporozoites, so no hypnozoites form

Only gametocytes are passed on by transfusion

Chloroquine also destroys the hypnozoites in the liver

Storage of the donor blood killed the liver stages

A 38-year-old man with HIV (CD4 count 60 cells/µL) has fever, headache and right-sided weakness. MRI shows several ring-enhancing lesions in the basal ganglia. Toxoplasma IgG is strongly positive and Toxoplasma IgM is negative. What is the best interpretation?

Reactivation of a latent Toxoplasma infection

Past infection that cannot explain the lesions

A false-positive IgG from raised globulins

Recent primary infection with Toxoplasma

Parasitology: protozoa

47 Kerala MSc MLT Entrance practice questions on Parasitology: protozoa, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A 30-year-old woman has a frothy, yellow-green vaginal discharge. Why should the saline wet mount for Trichomonas vaginalis be examined within minutes of collection?
1. AVaginal lactobacilli lyse the trophozoites
2. BThe trophozoites stop moving as they cool
3. CThe trophozoites turn into cysts outside the body
4. DClue cells soon hide the trophozoites
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Answer: B · The trophozoites stop moving as they cool
Trichomonas vaginalis is recognised in a wet mount by its jerky, twitching motility and its rippling undulating membrane. As the specimen cools and dries, the trophozoites round up and stop moving, and a motionless trichomonad is hard to tell from a pus cell. Even a prompt wet mount misses many infections, so culture or a nucleic acid test is used when the mount is negative. The parasite has no cyst stage and is transmitted as the trophozoite.
- A: Lactobacilli are reduced in trichomoniasis and do not lyse the parasite.
- C: Trichomonas vaginalis has no cyst stage; it exists only as a trophozoite.
- D: Clue cells mark bacterial vaginosis and do not hide motile trophozoites.
Question 2 · Medium
In the Sabin-Feldman dye test for toxoplasmosis, a serum containing specific antibody is shown by live tachyzoites that:
1. AStain deep blue with methylene blue
2. BClump together in visible agglutinates
3. CTurn green under ultraviolet light
4. DFail to take up alkaline methylene blue
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Answer: D · Fail to take up alkaline methylene blue
The dye test mixes live tachyzoites with the patient's serum and an accessory factor, a complement-like factor from normal human serum. Specific antibody with the accessory factor damages the parasite membrane, so the cytoplasm no longer takes up alkaline methylene blue and the tachyzoites look thin and colourless. Without antibody the parasites stain deep blue. The titre is the highest dilution at which half the parasites are unstained; because live organisms are needed, it is used as a reference test.
- A: Deep blue staining is the result when antibody is absent.
- B: The dye test reads staining, not agglutination; agglutination is a separate Toxoplasma test.
- C: Fluorescence is read in the indirect immunofluorescence test, not the dye test.
Question 3 · Easy
Which part of the Giardia duodenalis trophozoite holds it onto the duodenal mucosa?
1. AThe undulating membrane
2. BThe pair of median bodies
3. CThe ventral adhesive disc
4. DIts four pairs of flagella
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Answer: C · The ventral adhesive disc
The flat ventral surface of the Giardia trophozoite carries a concave adhesive (sucking) disc that grips the brush border of duodenal and jejunal cells. Heavy attachment flattens the villi and impairs fat absorption, giving the pale, greasy stools of giardiasis. Because the trophozoites cling to the mucosa, they may be missed in stool and found more easily in duodenal fluid. The flagella give the falling-leaf motility, and the median bodies are internal structures used in identification.
- A: An undulating membrane belongs to Trichomonas and trypanosomes, not Giardia.
- B: Median bodies are internal microtubule bundles used to identify Giardia, not for attachment.
- D: The flagella move the trophozoite; they do not attach it.
Question 4 · Hard
Two weeks after a blood transfusion in Kochi, a 60-year-old woman who has never left Kerala develops fever. Her thin film shows P. vivax with Schüffner's dots, and she is cured with chloroquine. Why is primaquine not needed for her?
1. ATransfused blood carries no sporozoites, so no hypnozoites form
2. BOnly gametocytes are passed on by transfusion
3. CChloroquine also destroys the hypnozoites in the liver
4. DStorage of the donor blood killed the liver stages
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Answer: A · Transfused blood carries no sporozoites, so no hypnozoites form
Transfusion malaria is started by asexual blood-stage parasites in the donor's red cells, which go straight into the recipient's red cells. Without sporozoites there is no liver (exoerythrocytic) cycle and so no hypnozoites, and relapse cannot occur. A blood schizonticide such as chloroquine therefore cures P. vivax acquired this way, and primaquine, given to kill hypnozoites, is not needed. Donor screening and questioning about recent fever are the main preventive measures.
- B: Asexual blood stages cause transfusion malaria; gametocytes alone could not cause the infection.
- C: Chloroquine kills blood stages only; primaquine is the drug that acts on hypnozoites.
- D: Liver stages are never present in donor blood, so storage has nothing to kill.
Question 5 · Hard
A 38-year-old man with HIV (CD4 count 60 cells/µL) has fever, headache and right-sided weakness. MRI shows several ring-enhancing lesions in the basal ganglia. Toxoplasma IgG is strongly positive and Toxoplasma IgM is negative. What is the best interpretation?
1. APast infection that cannot explain the lesions
2. BReactivation of a latent Toxoplasma infection
3. CA false-positive IgG from raised globulins
4. DRecent primary infection with Toxoplasma
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Answer: B · Reactivation of a latent Toxoplasma infection
Toxoplasmic encephalitis in AIDS almost always comes from reactivation of bradyzoite cysts acquired years earlier, once the CD4 count falls below about 100 cells/µL. These patients have IgG antibody, usually without IgM, because this is not a primary infection. A positive IgG with multiple ring-enhancing basal ganglia lesions therefore supports the diagnosis, while a negative IgG would make it unlikely. Response to empirical anti-Toxoplasma treatment, or PCR on CSF or biopsy tissue, confirms it.
- A: With a CD4 count under 100 and typical lesions, a positive IgG supports active disease rather than excluding it.
- C: Strongly positive specific IgG is not explained by raised globulins, and the picture fits Toxoplasma.
- D: A recent primary infection would usually show IgM; its absence fits reactivation.
Question 6 · Medium
In African trypanosomiasis, why does parasitaemia rise and fall in repeated waves?
1. AThe parasites hide as amastigotes in heart muscle
2. BThe parasites leave the blood for the liver each cycle
3. CThe tsetse fly reinfects the patient at intervals
4. DThe parasites keep switching their surface glycoprotein
Answer and explanation in LearnFree account
Question 7 · Medium
Why does Napier's formol-gel (aldehyde) test become positive in visceral leishmaniasis?
1. AA large polyclonal rise in serum IgG
2. BLarge numbers of circulating LD bodies
3. CA rise in serum albumin above normal
4. DAntibody binding to the rK39 antigen
Answer and explanation in LearnFree account
Question 8 · Easy
In the Plasmodium life cycle, the stage that must be swallowed by a female Anopheles for the mosquito to become infected is the:
1. ARing-stage trophozoite
2. BGametocyte
3. CSporozoite
4. DMerozoite
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Question 9 · Medium
Sporulated sporocysts about 15 x 10 µm, each holding four sporozoites, are found singly in the stool of a man who often eats undercooked beef. The most likely parasite is:
1. ASarcocystis hominis
2. BCystoisospora belli
3. CCryptosporidium parvum
4. DCyclospora cayetanensis
Answer and explanation in LearnFree account
Question 10 · Hard
A 25-year-old man in Kochi has had bloody diarrhoea and fever for 2 days. Stool wet mount: many pus cells (over 50 per high-power field), red cells, and a few large, non-motile cells 20-30 µm across with a big irregular nucleus and ingested red cells. The report reads 'Entamoeba histolytica trophozoites seen'. Next day the culture grows Shigella flexneri. The most likely explanation of the first report is:
1. AA mixed infection with both organisms
2. BEntamoeba dispar was misread as E. histolytica
3. CMacrophages were mistaken for trophozoites
4. DTrophozoites rounded up during transport
Answer and explanation in LearnFree account
Question 11 · Easy
Round oocysts 8-10 µm across that stain variably with modified acid-fast stain and glow under ultraviolet light are:
1. ACyclospora cayetanensis
2. BCystoisospora belli
3. CToxoplasma gondii
4. DCryptosporidium parvum
Answer and explanation in LearnFree account
Question 12 · Hard
A 28-year-old man has dysuria and a scanty urethral discharge; Gram stain shows pus cells but no Gram-negative diplococci. A fresh urine sediment shows pear-shaped cells about 15 µm long, slightly larger than pus cells, moving with a jerky, twitching motion. The most likely cause is:
1. AMotile spermatozoa
2. BGiardia from faecal contamination
3. CTrichomonas vaginalis
4. DFree-living flagellates from a dirty container
Answer and explanation in LearnFree account
Question 13 · Easy
How does the trypomastigote of Trypanosoma cruzi typically appear in a stained blood film?
1. ARound, with a rod-shaped kinetoplast and no flagellum
2. BCrescent-shaped, with a single central nucleus
3. CLong and slender, with a tiny kinetoplast
4. DC-shaped, with a large, bulging kinetoplast
Answer and explanation in LearnFree account
Question 14 · Medium
How is xenodiagnosis for Chagas disease carried out?
1. ACulturing the patient's blood on NNN medium for several weeks
2. BLetting clean triatomine bugs feed on the patient and examining their faeces
3. CInjecting parasite antigen into the skin and reading it at 48 hours
4. DInoculating the patient's blood into mice and examining their blood
Answer and explanation in LearnFree account
Question 15 · Medium
Among the intestinal coccidian parasites of humans, which one typically causes peripheral blood eosinophilia?
1. ASarcocystis hominis
2. BCyclospora cayetanensis
3. CCystoisospora belli
4. DCryptosporidium parvum
Answer and explanation in LearnFree account
Question 16 · Medium
The rK39 strip test is widely used for kala-azar in India. Its main limitation is that it:
1. AIs positive in most people with cutaneous leishmaniasis
2. BDetects parasite antigen only when splenic parasites are very high
3. CNeeds a fresh bone marrow aspirate as the test sample
4. DStays positive for years after cure, so it cannot diagnose relapse
Answer and explanation in LearnFree account
Question 17 · Medium
In a patient treated for Plasmodium falciparum malaria, an HRP-2 based rapid test is not used to judge whether treatment has worked, because HRP-2:
1. ADisappears from the blood within a few hours of treatment
2. BCross-reacts with P. vivax lactate dehydrogenase
3. CStays in the blood for weeks after the parasites are cleared
4. DIs produced by gametocytes, which survive standard treatment
Answer and explanation in LearnFree account
Question 18 · Medium
Trichomonas vaginalis can be told apart from the intestinal flagellate Pentatrichomonas hominis because its undulating membrane:
1. AIs absent, with flagella only at the front end
2. BReaches only about half the length of the body
3. CRuns the whole length and ends in a free flagellum
4. DLies along a ventral disc used for attachment
Answer and explanation in LearnFree account
Question 19 · Medium
In a healthy adult, acquired toxoplasmosis that causes symptoms most often presents as:
1. APainless cervical lymph node enlargement
2. BRing-enhancing lesions in the brain
3. CSevere watery diarrhoea
4. DRetinochoroiditis with loss of vision
Answer and explanation in LearnFree account
Question 20 · Hard
A trainee reports early ring forms in a thin film from a febrile patient whose malaria rapid test is negative. On review, the bodies are purple and granular with a pale halo, show no blue cytoplasm ring, lie on top of the red cells, and similar bodies lie free between cells. What are they?
1. AEarly P. falciparum ring forms
2. BHowell-Jolly bodies in red cells
3. CStain precipitate on the film
4. DPlatelets lying over red cells
Answer and explanation in LearnFree account
Question 21 · Medium
Giemsa or Leishman stain for malaria films is diluted with water buffered to pH 7.2 mainly so that:
1. ABackground white cells are removed from the film
2. BSchüffner's dots and parasite chromatin stain clearly
3. CThe parasite cytoplasm takes up the eosin and turns red
4. DThe red cells lyse completely in the thin film
Answer and explanation in LearnFree account
Question 22 · Medium
The intestinal ulcer of amoebic colitis is classically flask-shaped because the trophozoites:
1. AErode the full thickness of the wall at a single point
2. BInvade along the lymphatics and form tubercle-like nodules
3. CPass through the mucosa and spread sideways in the submucosa
4. DDestroy the mucosa widely but stop at the muscularis mucosae
Answer and explanation in LearnFree account
Question 23 · Easy
The LD bodies seen inside macrophages in a bone marrow smear in kala-azar are:
1. APromastigotes
2. BAmastigotes
3. CTrypomastigotes
4. DEpimastigotes
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Question 24 · Hard
A 46-year-old woman with HIV (CD4 count 140 cells/µL) has had watery diarrhoea for 2 months. Absolute eosinophil count is 900/µL (reference under 500/µL). Modified acid-fast stain of stool shows red, ellipsoidal oocysts about 25 x 13 µm. Which parasite is most likely?
1. ACryptosporidium parvum
2. BCyclospora cayetanensis
3. CMicrosporidia
4. DCystoisospora belli
Answer and explanation in LearnFree account
Question 25 · Medium
How does the timing of a primary Toxoplasma infection in pregnancy affect the fetus?
1. ATransmission rises with gestation, but damage is worst when infected early
2. BTransmission and damage are both greatest in the third trimester
3. CTransmission happens only in the first trimester, when damage is greatest
4. DTiming has no effect, as the fetus is infected in every case
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Parasitology: protozoa

A 30-year-old woman has a frothy, yellow-green vaginal discharge. Why should the saline wet mount for Trichomonas vaginalis be examined within minutes of collection?

In the Sabin-Feldman dye test for toxoplasmosis, a serum containing specific antibody is shown by live tachyzoites that:

Which part of the Giardia duodenalis trophozoite holds it onto the duodenal mucosa?

Two weeks after a blood transfusion in Kochi, a 60-year-old woman who has never left Kerala develops fever. Her thin film shows P. vivax with Schüffner's dots, and she is cured with chloroquine. Why is primaquine not needed for her?

A 38-year-old man with HIV (CD4 count 60 cells/µL) has fever, headache and right-sided weakness. MRI shows several ring-enhancing lesions in the basal ganglia. Toxoplasma IgG is strongly positive and Toxoplasma IgM is negative. What is the best interpretation?

In African trypanosomiasis, why does parasitaemia rise and fall in repeated waves?

Why does Napier's formol-gel (aldehyde) test become positive in visceral leishmaniasis?

In the Plasmodium life cycle, the stage that must be swallowed by a female Anopheles for the mosquito to become infected is the:

Sporulated sporocysts about 15 x 10 µm, each holding four sporozoites, are found singly in the stool of a man who often eats undercooked beef. The most likely parasite is:

Round oocysts 8-10 µm across that stain variably with modified acid-fast stain and glow under ultraviolet light are:

A 28-year-old man has dysuria and a scanty urethral discharge; Gram stain shows pus cells but no Gram-negative diplococci. A fresh urine sediment shows pear-shaped cells about 15 µm long, slightly larger than pus cells, moving with a jerky, twitching motion. The most likely cause is:

How does the trypomastigote of Trypanosoma cruzi typically appear in a stained blood film?

How is xenodiagnosis for Chagas disease carried out?

Among the intestinal coccidian parasites of humans, which one typically causes peripheral blood eosinophilia?

The rK39 strip test is widely used for kala-azar in India. Its main limitation is that it:

In a patient treated for Plasmodium falciparum malaria, an HRP-2 based rapid test is not used to judge whether treatment has worked, because HRP-2:

Trichomonas vaginalis can be told apart from the intestinal flagellate Pentatrichomonas hominis because its undulating membrane:

In a healthy adult, acquired toxoplasmosis that causes symptoms most often presents as:

A trainee reports early ring forms in a thin film from a febrile patient whose malaria rapid test is negative. On review, the bodies are purple and granular with a pale halo, show no blue cytoplasm ring, lie on top of the red cells, and similar bodies lie free between cells. What are they?

Giemsa or Leishman stain for malaria films is diluted with water buffered to pH 7.2 mainly so that:

The intestinal ulcer of amoebic colitis is classically flask-shaped because the trophozoites:

The LD bodies seen inside macrophages in a bone marrow smear in kala-azar are:

A 46-year-old woman with HIV (CD4 count 140 cells/µL) has had watery diarrhoea for 2 months. Absolute eosinophil count is 900/µL (reference under 500/µL). Modified acid-fast stain of stool shows red, ellipsoidal oocysts about 25 x 13 µm. Which parasite is most likely?

How does the timing of a primary Toxoplasma infection in pregnancy affect the fetus?