Parasitology: helminths

33 Kerala MSc MLT Entrance practice questions on Parasitology: helminths, 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.

1. Question 1 · Easy

   Unlike most other trematodes that infect humans, Schistosoma species:

   1. ANeed no snail intermediate host
   2. BHave separate male and female worms
   3. CLay operculated eggs
   4. DLive in the bile ducts

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   Answer: B · Have separate male and female worms

   Most flukes, such as Fasciola and Paragonimus, are hermaphrodite, but schistosomes have separate sexes. The female lies in the gynaecophoric canal of the male, and the pair live in the mesenteric or vesical venous plexuses. Their eggs have no operculum but carry a spine, and cercariae released from the snail host penetrate human skin. The other flukes infect when metacercariae are eaten.

   • A: Schistosomes, like all flukes, need a snail intermediate host.
   • C: Schistosome eggs have no operculum; operculated eggs belong to other flukes.
   • D: Schistosomes live in veins; bile-duct flukes include Fasciola and Clonorchis.

2. Question 2 · Easy

   Humans acquire Dracunculus medinensis, the guinea worm, by drinking water containing infected:

   1. AMosquito larvae
   2. BSmall freshwater fish
   3. CFreshwater snails
   4. DCyclops (water fleas)

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   Answer: D · Cyclops (water fleas)

   The female guinea worm emerges through a blister on the leg and releases larvae when the limb is put into water. The larvae are swallowed by Cyclops, a tiny crustacean, and develop to the infective stage inside it. People are infected by drinking unfiltered water containing these Cyclops; the larvae are released in the stomach and migrate to the tissues. Filtering drinking water through cloth broke the cycle, and India was certified free of dracunculiasis in 2000.

   • A: Mosquito larvae are not hosts of Dracunculus; mosquitoes carry filarial worms.
   • B: Fish carry Dibothriocephalus and some flukes, not the guinea worm.
   • C: Snails are intermediate hosts of flukes, not of the guinea worm.

3. Question 3 · Medium

   What is the sheath that surrounds the microfilaria of Wuchereria bancrofti?

   1. AA layer of host eosinophil granule proteins
   2. BA cuticle shed by the larva in the mosquito
   3. CThe stretched egg membrane around the embryo
   4. DA coat of host plasma proteins on the larval surface

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   Answer: C · The stretched egg membrane around the embryo

   Wuchereria and Brugia are ovoviviparous: the embryo uncoils inside the egg, and the thin egg membrane stretches to enclose the larva as a loose sheath. The sheath projects beyond the head and tail and is shed in the mosquito's midgut. Its presence, and the arrangement of nuclei in the tail, help identify microfilariae in stained films. Mansonella perstans and Onchocerca volvulus microfilariae are unsheathed.

   • A: Eosinophil proteins do not form the sheath.
   • B: The sheath is cast off in the mosquito; it is not formed there.
   • D: The sheath is of parasite origin, the egg membrane, not host protein.

4. Question 4 · Hard

   Ten days after a village feast where undercooked pork was served, several guests have fever, swelling around the eyes and severe muscle pain. One man's results: WBC 15,000/µL with 34% eosinophils; creatine kinase 2,600 U/L (reference 30-200 U/L); stool microscopy negative. The most likely cause is:

   1. AToxocara canis
   2. BTrichinella spiralis
   3. CTaenia solium cysticercosis
   4. DStrongyloides stercoralis

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   Answer: B · Trichinella spiralis

   Fever, periorbital oedema and myalgia in a cluster of people a week or two after eating undercooked pork are classic for trichinellosis. Larvae released from the meat mature in the gut, and the new larvae spread in the blood to encyst in striated muscle, causing marked eosinophilia and a raised creatine kinase. Stool examination is unhelpful; diagnosis is by serology and, if needed, a muscle biopsy showing coiled larvae. Cysticercosis follows swallowing eggs rather than eating meat and does not cause an outbreak like this.

   • A: Toxocara is acquired from eggs in dog-contaminated soil and does not raise creatine kinase.
   • C: Cysticercosis comes from swallowed T. solium eggs and does not cause an acute myositis outbreak after a meal.
   • D: Strongyloides is acquired through the skin and does not cause periorbital oedema with myositis.

5. Question 5 · Medium

   In the formol-ether (formalin-ethyl acetate) concentration method, what is the main role of the ether?

   1. AIt extracts fat and debris into the top layer
   2. BIt stains the nuclei of protozoan cysts
   3. CIt fixes and preserves the eggs and cysts
   4. DIt raises the density so that eggs float

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   Answer: A · It extracts fat and debris into the top layer

   Stool is fixed in formalin, strained, then shaken with ether or ethyl acetate and centrifuged. The solvent dissolves fat and pulls light debris upward, forming a plug of debris between the solvent on top and the formalin below. Eggs, larvae and cysts are heavier and collect in the sediment, which is examined unstained and with iodine. Formalin, not ether, fixes the parasites and makes the specimen safe to handle.

   • B: Nuclei are stained afterwards with iodine; ether does not stain.
   • C: Fixation is the job of the formalin, not the ether.
   • D: Flotation in a dense solution is the principle of salt or zinc sulfate methods.

6. Question 6 · Hard

   A Kato-Katz smear is made with a template delivering 41.7 mg of stool, and 52 Ascaris eggs are counted on it. What is the egg count per gram of stool?

   1. A2,168 eggs per gram
   2. B12,470 eggs per gram
   3. C1,248 eggs per gram
   4. D2,600 eggs per gram

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7. Question 7 · Easy

   The scolex of Taenia solium differs from that of Taenia saginata in having:

   1. AA rostellum with two rows of hooks
   2. BA single row of hooks on a retractile rostellum
   3. CFour suckers and no hooks at all
   4. DTwo slit-like sucking grooves

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8. Question 8 · Hard

   A 50-year-old plantation worker from Idukki on long-term prednisolone has eosinophilia, but three stool concentrates show no eggs. A Harada-Mori filter-paper culture of his stool shows, on day 7, unsheathed filariform larvae with a notched tail and an oesophagus about half the body length. Which parasite is this?

   1. ANecator americanus
   2. BTrichostrongylus orientalis
   3. CAncylostoma duodenale
   4. DStrongyloides stercoralis

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9. Question 9 · Medium

   Why is a human with hydatid disease a dead-end host for Echinococcus granulosus?

   1. AHuman antibody destroys all its protoscolices
   2. BIts larvae are unable to leave the human gut wall
   3. CIts cysts in human organs are not eaten by dogs
   4. DIts eggs cannot hatch in the human intestine

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10. Question 10 · Medium

    Kato-Katz thick smears examined for hookworm must be read within about an hour of preparation, because the hookworm eggs:

    1. AClear in the glycerol and become invisible
    2. BShrink below the size range used in counting
    3. CTake up too much malachite green to identify
    4. DHatch into rhabditiform larvae on the slide

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11. Question 11 · Hard

    A 58-year-old woman from Cherthala has had gross swelling of the right leg with thick, folded skin for 12 years. Two night blood films and a Knott's concentrate show no microfilariae. What best explains this?

    1. ALate obstructive filariasis often has no microfilaraemia
    2. BThe night samples were drawn too early in the evening
    3. CLymphoedema in Kerala is never due to filarial worms
    4. DBrugia malayi microfilariae are never seen in thick films

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12. Question 12 · Medium

    The Baermann funnel technique recovers Strongyloides larvae from stool by relying on the larvae:

    1. AFloating to the top of a dense salt solution
    2. BMigrating out of the stool into warm water
    3. CSticking to cellophane tape on the funnel wall
    4. DCollecting at the ether-water layer on spinning

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13. Question 13 · Easy

    Adult worms of Wuchereria bancrofti live in the human:

    1. ALymphatic vessels and lymph nodes
    2. BMucosa of the small intestine
    3. CSubcutaneous connective tissues
    4. DPortal and mesenteric veins

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14. Question 14 · Hard

    A 30-year-old estate worker carries an estimated 300 Ancylostoma duodenale worms. Assume each worm takes 0.2 mL of blood a day, his hemoglobin is 10 g/dL and 1 g of hemoglobin holds 3.4 mg of iron. His daily iron loss is about:

    1. A204 mg
    2. B20 mg
    3. C6 mg
    4. D2 mg

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15. Question 15 · Easy

    In human cystic echinococcosis, the organ most often holding the hydatid cyst is the:

    1. ALung
    2. BBrain
    3. CLiver
    4. DKidney

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16. Question 16 · Hard

    A school child's stool shows many elongated, thin-shelled eggs, about 90 µm long, filled with refractile granules, and no other egg type. What does this finding mean?

    1. AMale and female worms are present in large numbers
    2. BThey are artefacts and the report should be negative
    3. CThe eggs are fertile and will cause autoinfection in the gut
    4. DOnly female Ascaris worms are present; treatment is still needed

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17. Question 17 · Medium

    Strongyloides stercoralis infection can persist for decades in a person who has left the endemic area. What allows this?

    1. AEggs remain viable in the bowel for many years
    2. BAdult worms survive for several decades in the gut mucosa
    3. CRhabditiform larvae moult to filariform larvae inside the gut
    4. DEncysted larvae stay dormant for years in skeletal muscle

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18. Question 18 · Hard

    A 3-year-old who plays with puppies and eats soil has fever, an enlarged liver and WBC 28,000/µL with 45% eosinophils (reference 1-6%). Three stool examinations show no eggs or larvae. Which test best supports the likely diagnosis?

    1. ANight blood film for sheathed microfilariae
    2. BELISA for Toxocara excretory-secretory antigen
    3. CKato-Katz thick smear of a fresh stool sample
    4. DMuscle biopsy for encysted coiled larvae

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19. Question 19 · Medium

    Per worm, Ancylostoma duodenale causes more blood loss than Necator americanus because it:

    1. AAttaches to the gastric mucosa and erodes vessels
    2. BReleases a toxin that suppresses red cell production
    3. CLives in the colon, where the mucosa bleeds more
    4. DTakes about 0.2 mL of blood a day, against 0.03 mL

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20. Question 20 · Medium

    Ten days after eating raw vegetables, a 6-year-old has cough, wheeze and eosinophilia with fleeting lung shadows. Which nematode's larvae pass through the lungs and cause this picture?

    1. ADracunculus medinensis
    2. BEnterobius vermicularis
    3. CTrichuris trichiura
    4. DAscaris lumbricoides

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21. Question 21 · Medium

    A patient with suspected bancroftian filariasis cannot give a night blood sample. A daytime sample may still show microfilariae if it is taken:

    1. AAbout 45 minutes after an oral dose of diethylcarbamazine
    2. BImmediately after the patient has eaten a large, heavy meal
    3. CAfter the patient has rested quietly in bed for two hours
    4. DFrom the ear lobe instead of from a vein in the arm

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22. Question 22 · Medium

    Taenia eggs seen in a stool concentrate are reported only as 'Taenia species'. Why?

    1. ABoth species are cleared by the same drug and dose
    2. BOnly adult worms can be grown in culture for typing
    3. CThe eggs lose their identifying hooklets in formalin
    4. DT. solium and T. saginata eggs look identical

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23. Question 23 · Medium

    For Fasciola hepatica, Clonorchis sinensis and Paragonimus westermani, the stage that infects humans is the:

    1. ACiliated miracidium
    2. BEncysted metacercaria
    3. CSporocyst in the snail
    4. DFree-swimming cercaria

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24. Question 24 · Easy

    Long-standing urinary schistosomiasis due to Schistosoma haematobium is a recognised cause of which bladder cancer?

    1. AMucinous adenocarcinoma
    2. BSquamous cell carcinoma
    3. CSmall cell carcinoma
    4. DUrothelial papilloma

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25. Question 25 · Hard

    A 45-year-old sheep farmer suddenly coughs up a large amount of salty, clear fluid containing white, grape-skin-like membranes. Chest X-ray last month showed a round lung shadow. What should the laboratory look for in the sputum?

    1. AGolden-brown operculated eggs
    2. BProtoscolices and free hooklets
    3. CAcid-fast bacilli on a ZN smear
    4. DBranching septate fungal hyphae

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