MLT GlobeParasitology: Cestodes (tapeworms)
34 Parasitology MCQs on Cestodes (tapeworms) with answers and explanations.
A fisherman who often eats raw freshwater fish presents with macrocytic anaemia and a low serum vitamin B12. Operculated eggs are seen in his stool. Which parasite is responsible?
The fish tapeworm D. latum (Dibothriocephalus latus) absorbs vitamin B12 in the jejunum, causing megaloblastic anaemia; its eggs are operculated. The other parasites do not typically cause B12 deficiency.
Humans acquire Taenia saginata by eating undercooked meat from its intermediate host. Which animal is that?
Cysticercus bovis develops in cattle muscle; humans are the definitive host. Pigs are the intermediate host of T. solium, fish of Diphyllobothrium, and dogs are definitive hosts of Echinococcus.
Which of these helminths is a tapeworm rather than a fluke?
D. latum is a cestode (fish tapeworm). Fasciola (liver), Fasciolopsis (intestine) and Paragonimus (lung) are trematodes.
Taenia solium has a flat, segmented body with a scolex bearing suckers and hooks. To which helminth class does it belong?
Segmented, ribbon-like worms with a scolex are cestodes (tapeworms). Nematodes are unsegmented and cylindrical; trematodes are leaf-shaped and unsegmented.
Humans acquire intestinal Taenia infection by eating undercooked meat that contains which stage?
Cysticerci in beef or pork evaginate in the gut and develop into adult tapeworms. Ingesting T. solium eggs instead causes cysticercosis, not intestinal taeniasis.
Echinococcus granulosus, the cause of hydatid disease, is classified as a:
E. granulosus is a small cestode living in the dog intestine; its larval hydatid cyst develops in humans. It is not a protozoan.
Which parasite requires an intermediate host as well as a definitive host (an indirect life cycle)?
T. saginata needs cattle as intermediate hosts. Entamoeba, Giardia and hookworm complete their cycles with humans as the only host.
Which tapeworm lives as an adult in the intestine of dogs, the 'dog tapeworm' that causes hydatid cysts in humans?
Dogs are the definitive hosts of E. granulosus; humans and sheep acquire hydatid cysts by ingesting eggs from dog faeces.
Which feature does NOT describe tapeworms (cestodes)?
Cestodes are flat, segmented hermaphrodites. A cylindrical unsegmented body is characteristic of nematodes.
Ultrasound shows a liver cyst with daughter cysts in a shepherd; aspirated fluid contains protoscolices ('hydatid sand'). Which parasite?
Hydatid cysts with daughter cysts and protoscolices are the larval stage of E. granulosus, acquired from dog faeces.
Which parasitic infection is usually afebrile?
The dwarf tapeworm H. nana usually causes mild or no gut symptoms without fever. Naegleria meningoencephalitis, malaria and the invasive phase of trichinellosis all cause fever.
The fish (broad) tapeworm of humans is:
D. latum (now also Dibothriocephalus latus) is acquired from raw freshwater fish and can cause vitamin B12 deficiency. T. solium is the pork tapeworm.
A cestode is a:
Cestodes are segmented, flat tapeworms. Flukes are trematodes, while roundworms and hookworms are nematodes.
Taenia saginata is best classified as a(n):
The adult beef tapeworm lives in the human small intestine; humans do not develop tissue larvae of T. saginata. Trematodes are flukes.
A stool from a child in a crowded daycare shows small, thin-shelled eggs with polar filaments between the oncosphere and shell. Which cestode, known as the dwarf tapeworm, is responsible?
H. nana is the smallest human tapeworm; its eggs show polar filaments and it can autoinfect without an intermediate host. D. latum is the broad fish tapeworm, and Taenia species are large.
Why must spillage of hydatid cyst fluid be avoided during aspiration or surgery?
Cyst fluid is highly antigenic and contains protoscolices, so leakage can cause anaphylactic shock and secondary cysts.
The segments that make up the body of a tapeworm are called:
The strobila is a chain of proglottids; the scolex is the attachment organ at the head end.
Children usually acquire the dog tapeworm Dipylidium caninum by:
The larval stage develops in fleas, so children who swallow fleas while playing with pets become infected.
A patient who eats undercooked beef passes motile proglottids; India-ink injection shows 15–30 lateral uterine branches per side. Identify the tapeworm.
T. saginata (beef tapeworm) gravid proglottids have more than 12 lateral uterine branches per side. T. solium has 7–13, and the other two have different proglottid structure.
The larval stage of Taenia solium that forms cysts in pig muscle (and in human brain in neurocysticercosis) is called:
T. solium larvae are Cysticercus cellulosae. Cysticercus bovis belongs to T. saginata, cysticercoids to Hymenolepis, and hydatid cysts to Echinococcus.