A 26-year-old man from Sudan who now works in Abu Dhabi has eosinophilia of 1.8 × 10^9/L (reference under 0.5 × 10^9/L) and intermittent abdominal pain. Microscopy of a midday urine is negative. A Kato-Katz thick smear is made from his stool with a template that holds 41.7 mg of faeces. It contains 18 large, oval, light-brown eggs about 150 × 60 µm, each with a prominent spine on one side and a ciliated miracidium inside. The correct identification and egg count are:

Schistosoma mansoni, about 430 eggs per gram

Schistosoma haematobium, about 430 eggs per gram

Schistosoma mansoni, about 750 eggs per gram

Schistosoma mansoni, about 18 eggs per gram

Elongated eggs about 90 µm long, with a thin, irregular bumpy coat and a mass of disorganised refractile granules inside, are:

Unfertilized Ascaris lumbricoides eggs

Fertile Ascaris lumbricoides eggs

Helminths

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Helminths, 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 26-year-old man from Sudan who now works in Abu Dhabi has eosinophilia of 1.8 × 10^9/L (reference under 0.5 × 10^9/L) and intermittent abdominal pain. Microscopy of a midday urine is negative. A Kato-Katz thick smear is made from his stool with a template that holds 41.7 mg of faeces. It contains 18 large, oval, light-brown eggs about 150 × 60 µm, each with a prominent spine on one side and a ciliated miracidium inside. The correct identification and egg count are:
1. ASchistosoma mansoni, about 430 eggs per gram
2. BSchistosoma haematobium, about 430 eggs per gram
3. CSchistosoma mansoni, about 750 eggs per gram
4. DSchistosoma mansoni, about 18 eggs per gram
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Answer: A · Schistosoma mansoni, about 430 eggs per gram
Large oval eggs with a prominent lateral spine are those of Schistosoma mansoni, whose adults live in the mesenteric veins and release eggs into the stool. The Kato-Katz template holds 41.7 mg of faeces, so the count is multiplied by 24 (1,000 ÷ 41.7) to give eggs per gram: 18 × 24 = 432, about 430 eggs per gram. WHO classes S. mansoni infections with 400 or more eggs per gram as heavy, so this man has a heavy infection. The miracidium inside the eggs shows they are viable. S. haematobium has a terminal spine and is looked for in midday urine, which was negative here.
- B: S. haematobium eggs have a terminal spine and are found mainly in urine.
- C: 750 comes from multiplying by 41.7 instead of by 24 (1,000 ÷ 41.7).
- D: Eggs counted in 41.7 mg must be scaled up to 1 g.
Question 2 · Easy
Oval, thin-shelled eggs about 65 µm long, each with an embryo of 4-8 cells and a clear space under the shell, belong to:
1. AHookworm species
2. BTrichuris trichiura
3. CAscaris lumbricoides
4. DTaenia species
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Answer: A · Hookworm species
Hookworm eggs are oval, about 60-75 µm long, with a thin smooth shell and a cleaving embryo that stands back from the shell. Eggs of Necator americanus and Ancylostoma duodenale look the same, so they are reported as hookworm eggs. The embryo keeps developing if stool is not examined or preserved promptly. Chronic infection causes iron deficiency anemia from intestinal blood loss.
- B: Trichuris eggs are barrel-shaped with polar plugs.
- C: Fertile Ascaris eggs have a thick, mammillated coat.
- D: Taenia eggs are round with a radially striated shell and a six-hooked embryo.
Question 3 · Easy
A barrel-shaped brown egg about 50 µm long, with a clear plug at each end, is from:
1. AEnterobius vermicularis
2. BTrichuris trichiura
3. CAscaris lumbricoides
4. DA hookworm
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Answer: B · Trichuris trichiura
Trichuris trichiura (whipworm) eggs are barrel- or lemon-shaped, about 50-55 µm long, with a thick brown shell and a clear polar plug at each end. They are passed unembryonated and need weeks in soil to become infective. Heavy infection in children can cause chronic dysentery and rectal prolapse. The eggs are found by routine stool concentration.
- A: Enterobius eggs are flattened on one side and contain a larva.
- C: Fertile Ascaris eggs are round to oval with a thick, bumpy (mammillated) coat.
- D: Hookworm eggs are oval and thin-shelled, with a cleaving embryo.
Question 4 · Medium
Elongated eggs about 90 µm long, with a thin, irregular bumpy coat and a mass of disorganised refractile granules inside, are:
1. AUnfertilized Ascaris lumbricoides eggs
2. BHookworm eggs
3. CFertile Ascaris lumbricoides eggs
4. DFasciola hepatica eggs
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Answer: A · Unfertilized Ascaris lumbricoides eggs
Unfertilized Ascaris eggs are longer (about 85-95 µm) and narrower than fertile ones, with a thinner shell and an irregular mammillated layer. They are filled with refractile granules instead of a single-celled embryo. They come from female worms without males and can be the only eggs seen, so they must be recognised and reported. Decorticated eggs, which have lost the outer bumpy coat, can also be seen.
- B: Hookworm eggs are thin-shelled and smooth, with a cleaving embryo.
- C: Fertile eggs are rounder, 45-75 µm, with a thick shell and a single-celled embryo.
- D: Fasciola eggs are much larger, about 140 µm, with an operculum.
Question 5 · Medium
Rounded eggs about 80 x 60 µm, each holding a miracidium and bearing a tiny lateral knob, are found in the stool of a farmer from rural central China. The species is:
1. ASchistosoma haematobium
2. BFasciola hepatica
3. CSchistosoma mansoni
4. DSchistosoma japonicum
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Answer: D · Schistosoma japonicum
Schistosoma japonicum eggs are smaller and rounder than other schistosome eggs and have only a tiny lateral knob, which is often hidden by debris. They contain a mature miracidium and are passed in stool. S. mansoni eggs have a large lateral spine, and S. haematobium eggs have a terminal spine and are found mainly in urine. S. japonicum produces many eggs and can cause severe liver fibrosis.
- A: S. haematobium eggs have a terminal spine and are usually found in urine.
- B: Fasciola eggs are larger, have an operculum and contain no miracidium.
- C: S. mansoni eggs are larger and elongated, with a prominent lateral spine.
Question 6 · Hard
A stool from a farm worker was left unpreserved at room temperature for 2 days before testing. It shows rhabditiform larvae but no eggs. Why must the larvae be examined closely before Strongyloides stercoralis is reported?
1. ATrichuris eggs can hatch into look-alike larvae
2. BTaenia eggs can hatch into look-alike larvae
3. CAscaris eggs can hatch into look-alike larvae
4. DHookworm eggs can hatch into look-alike larvae
Answer and explanation in LearnFree account
Question 7 · Medium
In the agar plate culture for Strongyloides stercoralis, a positive result is recognised by:
1. AClear zones of hemolysis around the stool
2. BA color change in a pH indicator in the agar
3. CBlack colonies from hydrogen sulfide made by larvae
4. DTracks of bacterial colonies left by crawling larvae
Answer and explanation in LearnFree account
Question 8 · Hard
A man who often eats raw freshwater fish has a macrocytic anemia. His stool contains oval, operculated, unembryonated eggs about 65 µm long with a small knob at the end opposite the operculum. Which parasite is most likely?
1. AClonorchis sinensis
2. BParagonimus westermani
3. CDibothriocephalus latus
4. DFasciola hepatica
Answer and explanation in LearnFree account
Question 9 · Hard
India ink injected into a gravid tapeworm proglottid shows 9 main lateral uterine branches on each side. Which identification, with its key implication, is correct?
1. ATaenia solium: its eggs are harmless to laboratory staff
2. BTaenia solium: its eggs can cause human cysticercosis
3. CTaenia saginata: its eggs can cause human cysticercosis
4. DTaenia saginata: acquired from undercooked beef only
Answer and explanation in LearnFree account
Question 10 · Medium
A stool concentrate contains large, ellipsoidal, unembryonated eggs about 140 µm long, each with a small operculum. They should be reported as:
1. ASchistosoma mansoni/S. japonicum
2. BParagonimus species
3. CFasciola hepatica/Fasciolopsis buski
4. DClonorchis/Opisthorchis species
Answer and explanation in LearnFree account

Helminths

Oval, thin-shelled eggs about 65 µm long, each with an embryo of 4-8 cells and a clear space under the shell, belong to:

A barrel-shaped brown egg about 50 µm long, with a clear plug at each end, is from:

Elongated eggs about 90 µm long, with a thin, irregular bumpy coat and a mass of disorganised refractile granules inside, are:

Rounded eggs about 80 x 60 µm, each holding a miracidium and bearing a tiny lateral knob, are found in the stool of a farmer from rural central China. The species is:

A stool from a farm worker was left unpreserved at room temperature for 2 days before testing. It shows rhabditiform larvae but no eggs. Why must the larvae be examined closely before Strongyloides stercoralis is reported?

In the agar plate culture for Strongyloides stercoralis, a positive result is recognised by:

A man who often eats raw freshwater fish has a macrocytic anemia. His stool contains oval, operculated, unembryonated eggs about 65 µm long with a small knob at the end opposite the operculum. Which parasite is most likely?

India ink injected into a gravid tapeworm proglottid shows 9 main lateral uterine branches on each side. Which identification, with its key implication, is correct?

A stool concentrate contains large, ellipsoidal, unembryonated eggs about 140 µm long, each with a small operculum. They should be reported as: