A man from southern India with lymphedema of one leg is tested for Wuchereria bancrofti. When should the blood sample for microfilariae be drawn?

At any time, as counts stay constant

Early in the morning, before breakfast

In P. falciparum malaria, finding many mature trophozoites and schizonts in the peripheral blood film matters because it:

Suggests a heavy, severe infection

Means the parasites are drug resistant

Shows that a second species is present

Shows that the infection is resolving

Blood and tissue parasites

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Blood and tissue parasites, part of Microbiology. The first 10 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 · Hard
A 40-year-old man from Uganda is treated in Abu Dhabi with intravenous artesunate for Plasmodium falciparum malaria. His day-0 thick film density was 20,000 asexual parasites/µL. On day 3 he is still febrile. The day-3 thick film shows 180 asexual parasites and 60 gametocytes counted against 200 white cells, and his WBC count that morning is 3.5 × 10^9/L. The hospital protocol flags possible early treatment failure when the day-3 asexual density is 25% or more of the day-0 density. Which result is correct?
1. A4,200/µL, below 25% of day 0
2. B31,500/µL, above 25% of day 0
3. C3,150/µL, below 25% of day 0
4. D7,200/µL, above 25% of day 0
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Answer: C · 3,150/µL, below 25% of day 0
Thick-film density = (asexual parasites counted ÷ white cells counted) × WBC count per µL. With the measured WBC count of 3,500/µL: 180 ÷ 200 × 3,500 = 3,150 asexual parasites/µL. This is about 16% of the day-0 density of 20,000/µL, below the 25% flag, so the parasites are clearing despite the fever. Gametocytes are counted and reported separately, because artesunate does not clear mature gametocytes quickly and their presence is not a sign of treatment failure. The assumed value of 8,000 white cells/µL is used only when no WBC count is available.
- A: 4,200 wrongly includes the gametocytes in the asexual density.
- B: 31,500 comes from dividing by 20 instead of by 200 white cells.
- D: 7,200 assumes 8,000 white cells/µL, but the measured count must be used.
Question 2 · Medium
A man from southern India with lymphedema of one leg is tested for Wuchereria bancrofti. When should the blood sample for microfilariae be drawn?
1. ABetween about 10 pm and 2 am
2. BAt any time, as counts stay constant
3. CBetween about 10 am and 2 pm
4. DEarly in the morning, before breakfast
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Answer: A · Between about 10 pm and 2 am
W. bancrofti in most of Asia and Africa shows nocturnal periodicity: microfilariae circulate in peripheral blood mainly at night, peaking around midnight, and stay in the lung capillaries by day. A sample taken between about 10 pm and 2 am gives the best yield, and a concentration method such as membrane filtration or Knott's technique improves sensitivity. Loa loa shows the opposite, daytime periodicity. Antigen tests for W. bancrofti can be done on blood taken at any time.
- B: Microfilarial counts in peripheral blood vary strongly over 24 hours.
- C: Midday sampling suits Loa loa, which has daytime periodicity.
- D: Fasting has no effect; the timing follows the parasite's night-time cycle.
Question 3 · Easy
Which Plasmodium species forms dormant liver hypnozoites that can cause relapses months after the first attack?
1. APlasmodium malariae
2. BPlasmodium knowlesi
3. CPlasmodium falciparum
4. DPlasmodium vivax
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Answer: D · Plasmodium vivax
P. vivax and P. ovale form hypnozoites, dormant liver stages that can reactivate weeks to months later and cause relapse. Treating the blood stages alone does not remove them, so a drug such as primaquine or tafenoquine is added after G6PD testing. P. vivax is common in malaria imported from South Asia. P. malariae can persist at low levels in the blood for years, but it does not form hypnozoites.
- A: P. malariae can recrudesce from long-lasting blood stages, not liver hypnozoites.
- B: P. knowlesi has no dormant liver stage.
- C: P. falciparum has no hypnozoites; late illness comes from untreated blood-stage infection.
Question 4 · Easy
Leishmania parasites are transmitted to people by the bite of:
1. ATriatomine (reduviid) bugs
2. BFemale Anopheles mosquitoes
3. CTsetse flies
4. DFemale phlebotomine sand flies
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Answer: D · Female phlebotomine sand flies
Leishmania is spread by female phlebotomine sand flies (Phlebotomus in the Old World, Lutzomyia in the Americas), which inject promastigotes while feeding. In the human host the parasites live inside macrophages as amastigotes. Cutaneous leishmaniasis occurs in parts of the Middle East and North Africa, and visceral disease in East Africa and South Asia. Tsetse flies and triatomine bugs transmit trypanosomes.
- A: Triatomine bugs transmit Trypanosoma cruzi.
- B: Anopheles mosquitoes transmit Plasmodium.
- C: Tsetse flies transmit African trypanosomes.
Question 5 · Medium
In P. falciparum malaria, finding many mature trophozoites and schizonts in the peripheral blood film matters because it:
1. ASuggests a heavy, severe infection
2. BMeans the parasites are drug resistant
3. CShows that a second species is present
4. DShows that the infection is resolving
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Answer: A · Suggests a heavy, severe infection
Red cells holding mature P. falciparum trophozoites and schizonts stick to the walls of small vessels (sequestration), so normally only rings and gametocytes are seen in peripheral blood. When many mature stages appear in the film, it suggests a large sequestered parasite load and a higher risk of severe malaria. The finding should be reported to the clinician urgently. Malaria pigment in more than 5% of neutrophils is another marker of poor prognosis.
- B: The mix of stages on a film does not show drug resistance.
- C: Falciparum's own schizonts can appear in severe infection; no second species is needed.
- D: Mature stages in the film point to a larger burden, not recovery.
Question 6 · Medium
A thin film shows slightly enlarged oval red cells, many with ragged (fimbriated) edges and Schüffner's dots, holding compact trophozoites. Mature schizonts contain about 8 merozoites. The species is most likely:
1. APlasmodium malariae
2. BPlasmodium ovale
3. CPlasmodium vivax
4. DPlasmodium falciparum
Answer and explanation in LearnFree account
Question 7 · Hard
A thin film from a traveller with P. falciparum malaria is examined. Among 1,000 red cells, 38 contain ring forms and 4 others contain gametocytes. The laboratory reports asexual parasitemia. What is the result?
1. A0.38%
2. B4.2%
3. C3.8%
4. D38%
Answer and explanation in LearnFree account
Question 8 · Hard
A night blood film from a man from Kerala, India shows sheathed microfilariae. The sheath stains pink with Giemsa, and the tapering tail holds two separate nuclei, one at the very tip. The species is most likely:
1. ABrugia malayi
2. BMansonella perstans
3. CWuchereria bancrofti
4. DLoa loa
Answer and explanation in LearnFree account
Question 9 · Hard
A worker recently arrived from Eritrea has fever. The thin film shows P. falciparum rings and crescent-shaped gametocytes at 0.4% parasitemia. The rapid test is negative on its HRP2 line but positive on its pan-pLDH line. The most likely explanation is:
1. AA prozone effect from high parasitemia
2. BA mixed infection with Plasmodium vivax
3. CPersisting antigen from a past infection
4. DParasites lacking the pfhrp2/pfhrp3 genes
Answer and explanation in LearnFree account
Question 10 · Medium
For microscopy in suspected cutaneous leishmaniasis, the skin sample should be taken from:
1. AThe crust over the center of the ulcer
2. BThe pus at the base of the ulcer
3. CNormal skin next to the lesion
4. DThe raised, active edge of the lesion
Answer and explanation in LearnFree account

Blood and tissue parasites

A man from southern India with lymphedema of one leg is tested for Wuchereria bancrofti. When should the blood sample for microfilariae be drawn?

Which Plasmodium species forms dormant liver hypnozoites that can cause relapses months after the first attack?

Leishmania parasites are transmitted to people by the bite of:

In P. falciparum malaria, finding many mature trophozoites and schizonts in the peripheral blood film matters because it:

A thin film shows slightly enlarged oval red cells, many with ragged (fimbriated) edges and Schüffner's dots, holding compact trophozoites. Mature schizonts contain about 8 merozoites. The species is most likely:

A thin film from a traveller with P. falciparum malaria is examined. Among 1,000 red cells, 38 contain ring forms and 4 others contain gametocytes. The laboratory reports asexual parasitemia. What is the result?

A night blood film from a man from Kerala, India shows sheathed microfilariae. The sheath stains pink with Giemsa, and the tapering tail holds two separate nuclei, one at the very tip. The species is most likely:

A worker recently arrived from Eritrea has fever. The thin film shows P. falciparum rings and crescent-shaped gametocytes at 0.4% parasitemia. The rapid test is negative on its HRP2 line but positive on its pan-pLDH line. The most likely explanation is:

For microscopy in suspected cutaneous leishmaniasis, the skin sample should be taken from: