Question 1

Which of the following best explains the pattern of trypanosome population changes shown in the first image, where different clones (A, B, C) rise and fall in succession over several weeks after infection?

Accepted Answer

The host's immune system eliminates each clone as it appears, but the parasite evades immunity by antigenic variation, allowing new clones to emerge.

Question 2

The second image shows a person with severe swelling and thickening of the lower limbs. Which parasitic infection is most likely responsible for this condition, and what is the underlying mechanism?

Accepted Answer

Filarial elephantiasis caused by Wuchereria bancrofti, due to obstruction of lymphatic vessels by adult worms.

Question 3

The third image shows a heart with numerous white, thread-like structures. Which parasite is responsible for this pathology, and what is a common clinical consequence in dogs?

Accepted Answer

Dirofilaria immitis (dog heartworm); can cause heart failure due to obstruction and tissue damage.

Question 4

Which stage of Entamoeba histolytica, shown in the fourth and fifth images, is responsible for transmission to new hosts, and why?

Accepted Answer

The cyst stage, because it is protected by a thick wall and survives outside the host.

Question 5

A patient presents with severe eye pain and vision loss after using homemade saline solution for contact lenses. The eighth image shows a cloudy cornea. Which parasite is most likely responsible, and what is the typical route of infection?

Accepted Answer

Acanthamoeba, which infects the cornea through contaminated water or poor contact lens hygiene.

Question 6

Balantidium coli, shown in the ninth and tenth images, is unique among protozoan parasites of humans because:

Accepted Answer

It is the only ciliate known to infect humans.

Question 7

Which of the following best describes the life cycle of Balantidium coli, as illustrated in the images and text?

Accepted Answer

Cysts are ingested, excyst in the small intestine, trophozoites multiply in the large intestine, and cysts are released in feces.

Question 8

A patient develops watery, frothy diarrhea after drinking untreated stream water while camping. The organism is resistant to chlorine but can be removed by filtration. Which parasite is most likely responsible, and what is its main mode of attachment in the intestine?

Accepted Answer

Giardia lamblia; attaches to the intestinal wall using an adhesive disk.

Question 9

Which of the following statements about Trichomonas vaginalis is correct?

Accepted Answer

It exists only as a trophozoite and is primarily transmitted by sexual contact.

Question 10

A major waterborne outbreak of diarrhea in Milwaukee in 1993 was caused by which protozoan, and why was standard water treatment ineffective?

Accepted Answer

Cryptosporidium parvum; its oocysts are resistant to chlorination and ozone.

Question 11

Which of the following best explains why Plasmodium falciparum infection can lead to severe anemia and jaundice?

Accepted Answer

Destruction of erythrocytes during the asexual blood stage releases hemoglobin, leading to hemolysis and jaundice.

Question 12

A pregnant woman is advised to avoid cleaning cat litter boxes to prevent infection with which parasite, and what is the risk to the fetus?

Accepted Answer

Toxoplasma gondii; risk of congenital toxoplasmosis causing physical or mental retardation.

Question 13

Trypanosoma brucei, the causative agent of African sleeping sickness, evades the host immune system primarily by which mechanism?

Accepted Answer

Antigenic variation, changing its surface glycoproteins to avoid antibody detection.

Question 14

A cattle farmer in Africa is unable to keep livestock due to a disease that causes chronic wasting in cattle. Which parasite is responsible, and what is the disease called?

Accepted Answer

Trypanosoma species; the disease is called Nagana.

Question 15

Which of the following statements about schistosome (blood fluke) infection is correct?

Accepted Answer

The life cycle requires a snail intermediate host, and infection occurs when cercariae penetrate human skin.

Question 16

A patient presents with chronic cough and orange-brown flecks in their sputum after eating undercooked crab. Which parasite is most likely responsible, and what is a possible complication?

Accepted Answer

Paragonimus westermani (Oriental lung fluke); complication includes chronic tuberculosis-like lung disease.

Question 17

Which structure of the tapeworm is responsible for attachment to the host's intestine, and what is its function?

Accepted Answer

Scolex; it uses hooks and suckers to anchor the worm to the intestinal wall.

Question 18

A child in North America is found to have intense perianal itching, especially at night. Which parasite is most likely responsible, and how is the infection typically diagnosed?

Accepted Answer

Enterobius vermicularis (pinworm); diagnosis is by finding eggs on the perianal skin.

Question 19

A person develops a severe intestinal blockage after eating vegetables grown in soil fertilized with human feces. The parasite is a large roundworm that migrates through the lungs during its life cycle. Which parasite is responsible, and what is a key step in its life cycle?

Accepted Answer

Ascaris lumbricoides; larvae migrate from the intestine to the lungs and are then coughed up and swallowed.

Study Notes: Medically Important Parasites and Protozoa

Study Guide - Practice Questions

Study Guide - Flashcards