Parasitology Questions and Answers

Answer: D

The correct match is P-(iii), Q-(i), R-(iv), S-(ii).

• Ascaris lumbricoides, the large roundworm, lives as an adult in the small intestine (iii).
• Dracunculus medinensis, the guinea worm, lives in subcutaneous tissue; the female emerges through a blister, usually on the leg (i).
• Enterobius vermicularis, the pinworm, lives in the caecum and appendix and migrates to the perianal skin to lay eggs (iv).
• Wuchereria bancrofti adults live in the lymphatic vessels and lymph nodes, causing lymphatic filariasis and elephantiasis (ii).

Options A, B and C each put the guinea worm or the filarial worm in the wrong tissue.

Answer: D

The correct match is P-2 ; Q-1 ; R-4 ; S-3.

• African sleeping sickness is caused by Trypanosoma brucei, spread by the tsetse fly.
• Chagas disease, in the Americas, is caused by Trypanosoma cruzi, spread by triatomine (kissing) bugs.
• Elephantiasis (lymphatic filariasis) is caused by the nematode Wuchereria bancrofti, spread by mosquitoes.
• Lyme disease is caused by the spirochaete Borrelia burgdorferi, spread by ticks.

Rickettsia rickettsii causes Rocky Mountain spotted fever and matches none of the four. The option with P-2 but Q-4 and R-1 swaps the filarial worm and T. cruzi, and the others misplace the trypanosomes.

Answer: B

Toxoplasma gondii is a parasite; it is the only term the key accepts in this multiple-select question.

T. gondii is a protozoan of the phylum Apicomplexa, related to the malaria parasite. It is an obligate intracellular parasite: it can multiply only inside host cells. Cats are its definitive hosts, where sexual reproduction takes place, while humans and many other warm-blooded animals act as intermediate hosts, infected through oocysts or tissue cysts in undercooked meat.

It is a eukaryotic cell with a nucleus and organelles, so it is not a virus or a bacterium, and it is a protozoan rather than a fungus.

Answer: B

Exo-erythrocytic schizogony occurs in the Liver.

The sporozoites injected by the mosquito travel in the blood to the liver and enter hepatocytes. There they multiply asexually by schizogony, outside red cells (hence exo-erythrocytic), and release thousands of merozoites.

Only those merozoites then invade red blood cells and begin erythrocytic schizogony, which causes the fever. 'Blood' is too vague and is where the merozoites travel, and in the mosquito the stage is sporogony, with oocysts on the stomach wall, not schizogony.

Answer: D

Both are transmitted by Mosquitoes.

Yellow fever virus is spread mainly by Aedes mosquitoes, especially Aedes aegypti, and West Nile virus mainly by Culex mosquitoes, with birds as its main reservoir.

Ticks transmit diseases such as Lyme disease and Kyasanur Forest disease, kissing bugs (triatomines) transmit Chagas disease, and deer flies transmit tularaemia and loiasis. None of them is the vector of these two fevers.

Answer: A

The true combination is sand fly and Leishmania.

Kala-azar, visceral leishmaniasis, is caused by the protozoan Leishmania donovani. It is transmitted by the bite of the female sand fly, Phlebotomus argentipes in India. The parasite multiplies in macrophages of the spleen, liver and bone marrow, causing fever, an enlarged spleen and greyish skin, the 'black fever' of the name.

The tsetse fly (Glossina) and Trypanosoma cause African sleeping sickness. Mosquitoes and Plasmodium cause malaria, and mosquitoes and microfilarial worms cause lymphatic filariasis.

Answer: A

Parasites living on the body surface of the host constitute an Infestation.

The term is used for ectoparasites such as lice, ticks, mites and fleas, which live on the skin or hair rather than inside the body. Infection is the corresponding term for the entry and multiplication of a parasite or microbe inside the host's tissues, for example a bacterial or protozoan infection.

Pollution refers to harmful substances in the environment, and contamination to the presence of an agent on objects or in food, water or wounds; neither describes a parasite living on a host.

Answer: A

The free-living group is Turbellaria.

Turbellarians, such as the planarian Dugesia, are flatworms living in fresh water, the sea and damp soil. They are solitary, ciliated and free living, gliding over surfaces and feeding as predators or scavengers.

The other two flatworm classes are entirely parasitic: Trematoda (flukes such as Fasciola and Schistosoma) and Cestoda (tapeworms such as Taenia). Nematoda includes many free-living roundworms, but the question asks for the group whose representatives are free living, and among the helminths it is the Turbellaria that are standardly described this way.

Answer: B

The stage that does not occur in the liver fluke is the Cystecircus (cysticercus).

The life cycle of Fasciola hepatica runs: egg, miracidium (which enters a snail), sporocyst, redia, cercaria (which leaves the snail), and metacercaria (the cyst on vegetation eaten by sheep or cattle). The adult then develops in the bile ducts.

The cysticercus, or bladder worm, is the larva of tapeworms such as Taenia solium, found in the muscles of pigs. It belongs to the cestode life cycle, not the trematode one. Cercaria, metacercaria and sporocysts all occur in Fasciola.

Answer: B

The process is apolysis.

In tapeworms (class Cestoda), new proglottids form behind the neck and mature as they are pushed back. The terminal gravid proglottids, filled with eggs, detach from the strobila and are passed out with the host's faeces. This shedding is called apolysis.

Apoptosis is programmed death of individual cells, not detachment of body segments. 'Homolysis' and 'genolysis' are not terms for this process.