BCSE Veterinary Parasitology

Question 1

A dog presents with a pot-bellied appearance, poor coat, and a positive fecal flotation showing oval eggs with thick, mammillated shells. Which parasite is most likely responsible?

Accepted Answer

Toxocara canis

Answer

Toxocara canis produces large, oval eggs with a thick, pitted (mammillated) outer shell. Ascarid infections are common in puppies and can cause pot-bellied appearance and poor thrift. Ancylostoma produces thin-shelled eggs, Trichuris produces barrel-shaped eggs with bipolar plugs, and Dipylidium proglottids contain egg packets not individual eggs.

Question 2

Which of the following Plasmodium-like protozoa infects cattle erythrocytes, is transmitted by Ixodes ticks, and can cause severe hemolytic anemia in splenectomized animals?

Accepted Answer

Babesia bovis

Answer

Babesia bovis is an intraerythrocytic protozoan transmitted by Rhipicephalus (Boophilus) microplus ticks that causes bovine babesiosis (redwater fever). Splenectomized animals are especially vulnerable because the spleen normally removes parasitized red cells. Theileria infects lymphocytes first, Trypanosoma is flagellated and extracellular, and Anaplasma is a rickettsial organism, not a protozoan.

Question 3

Ivermectin exerts its antiparasitic effect primarily by:

Accepted Answer

Potentiating glutamate-gated chloride channels, causing paralysis

Answer

Ivermectin binds to glutamate-gated chloride channels (and to a lesser degree GABA-gated channels) in invertebrate nerve and muscle cells, causing hyperpolarization and irreversible paralysis. Benzimidazoles inhibit tubulin polymerization; organophosphates block acetylcholinesterase; and antiprotozoals like atovaquone target mitochondrial transport.

Question 4

The intermediate host responsible for transmission of Taenia solium cysticercosis to humans is:

Accepted Answer

Pigs ingesting tapeworm eggs

Answer

Taenia solium uses pigs as the intermediate host. Pigs ingest proglottids or eggs shed in human feces; oncospheres hatch and develop into cysticerci in pig muscle (pork measles). Humans become definitive hosts by eating undercooked pork. Taenia saginata uses cattle. Dipylidium requires fleas. Mosquitoes transmit filarial nematodes, not cestodes.

Question 5

Giardia duodenalis trophozoites are best characterized by which morphological feature on a fecal smear?

Accepted Answer

Two nuclei and a ventral adhesive disc giving a 'falling leaf' motility

Answer

Giardia trophozoites are binucleate, pear-shaped flagellates with a concave ventral adhesive disc used to attach to intestinal epithelium. Their characteristic 'falling leaf' tumbling motility is seen in fresh wet mounts. Cysts (not trophozoites) contain 4 nuclei. Tritrichomonas has an undulating membrane and single nucleus. Axostyle prominence is a feature of Trichomonas.

BCSE - Basic and Clinical Sciences Examination Practice Test

BCSE - Basic and Clinical Sciences Examination Practice Test

BCSE Veterinary Parasitology