Question 1

A biology graduate student who recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye. She tells you that she is concerned because she had been warned about eye disease transmitted by black flies. When in Africa, she was in a river area, and despite her best efforts she received a lot of black fly bites. She also has some subcutaneous nodules. If her infection was acquired by black fly bite, what is the most likely causative agent?

A) Ancylostoma braziliense
B) Dracunculus medinensis
C) Loa loa
D) Onchocerca volvulus
E) Wuchereria bancrofti

Onchocerca volvulus

Accepted Answer

Onchocerca volvulus causes river blindness and is transmitted by the bite of a black fly. The patient may be able to detect movement of the parasite in the eye.

Question 2

A woman who imports food from Mexico and spends several months per year in rural Mexico had to have a compound leg fracture pinned and set in Mexico and has returned 3 days later. She now has signs of acute appendicitis and is taken to surgery in Houston. When her appendix is removed, it is found to contain a light-colored, 20.5-cm-long roundworm as well as bile-stained, knobby eggs consistent with Ascaris. How did she acquire this infection?

A) Ingestion of water containing filariform larvae
B) Skin penetration by filariform larvae
C) Skin penetration by rhabditiform larvae
D) Ingestion of food contaminated with the eggs
E) Inhalation of dust carrying the cysts

Ingestion of food contaminated with the eggs

Accepted Answer

Fertilized Ascaris eggs released in feces may contaminate food or water, which is then consumed. Ascaris does not attach to the intestine but maintains its position by mobility. The worm may become hypermotile (e.g., during febrile periods, anesthetic use, or antibiotic use) and may migrate into the appendix or bile duct.

Question 3

A patient whose major source of protein is smoked and cooked fish develops what appears to be pernicious anemia. What parasite is noted for causing a look-alike vitamin B12 anemia in certain genetically predisposed infected individuals?

A) Echinococcus granulosus
B) Diphyllobothrium latum
C) Hymenolepis nana
D) Dipylidium caninum
E) Taenia solium

Diphyllobothrium latum

Accepted Answer

Diphyllobothrium is the tapeworm associated with anemia. It is transmitted in fish found in cool lake regions.

Question 4

Which of the following protozoans is free living and is such that acquisition does not generally indicate fecal contamination?&#10;A) Acanthamoeba&#10;B) Dientamoeba fragilis&#10;C) Entamoeba histolytica&#10;D) Entamoeba coli&#10;E) Giardia

Accepted Answer

Acanthamoeba is a free-living organism with a sturdy cyst stage that is found in dust. A common way of acquiring Acanthamoeba infections in the United States is through homemade saline solutions for soft contact lenses. Giardia may be from animal contamination of water (rather than human) but is still not probably truly free living.

Question 5

A 26-year-old woman with uncomplicated malaria who was treated initially with chloroquine now has relapsed. What is the reason for a chloroquine-treated case of Plasmodium vivax relapsing?&#10;A) P. vivax has a significant level of chloroquine resistance.&#10;B) P. vivax has a persistent erythrocytic stage.&#10;C) P. vivax has a persistent exoerythrocytic stage (hypnozoite).&#10;D) Chloroquine is not one of the drugs of choice.

Accepted Answer

Both Plasmodium ovale and Plasmodium vivax may have resting liver forms, which are very slow to develop into schizonts with merozoites and proceed onto the chloroquine-sensitive erythrocytic stages after treatment is over. (It is not over with P. ovale or P. vivax unless you also treat with primaquine phosphate, which kills the liver stages.) (Papua, New Guinea, and Indonesia now have chloroquine-resistant Plasmodium vivax.)

Question 6

How is Leishmania donovani transmitted?&#10;A) Anopheles mosquito bite&#10;B) Black fly bite&#10;C) Culex mosquito bite&#10;D) Sandfly bite&#10;E) Skin penetration by trauma

Accepted Answer

All leishmaniae are transmitted by sandflies.

Question 7

How is Schistosoma haematobium transmitted?&#10;A) Ingestion of raw or undercooked snail, frog, or snake&#10;B) Invasion of filariform larvae from soil&#10;C) Handling aquatic birds&#10;D) Standing or swimming in contaminated water&#10;E) Tsetse fly bite

Accepted Answer

All schistosomes are transmitted by skin penetration from standing or swimming in contaminated water. Remember that snails are intermediate hosts.

Question 8

An untreated AIDS patient $(CD4^4 count of 180 cells/mm^3)$ from southern California has developed a progressively severe headache and mental confusion, along with ataxia and retinochoroiditis. Focal lesions are present on a computed tomography scan of his brain. No mucocutaneous lesions are found. He has been living under a bridge for the past 2 years. His level of immunoglobulin G (IgG) to the infectious agent is high. What is the most likely explanation for how this current infection started?

A) Earlier exposure to pigeons
B) Earlier exposure to desert sand
C) Reactivation of bradyzoites in cysts from an earlier infection
D) Recent exposure to cat feces
E) Recent exposure to bats

Accepted Answer

The most likely disease in this case is encephalitis with focal lesions. Because the patient has high levels of immunoglobulin G, the current infection is likely a reactivation of an earlier infection; therefore, recent exposures (choices D and E) can be eliminated. Exposure to pigeons suggests cryptococcosis, which is often a reactivational infection. However, in cryptococcosis antibody levels are rarely monitored, and there is no mention of India ink stain or capsular polysaccharide in the cerebrospinal fluid, which are the major diagnostic methods. In addition, based on the patient's symptoms, the infection is more likely to be encephalitis rather than meningitis or meningoencephalitis; also, retinochoroiditis is usually not present in cryptococcosis. The retinochoroiditis and lack of mucocutaneous lesions makes infection with Coccidioides less likely. Reactivation of toxoplasmosis is most likely.

Question 9

Which of the following is the tapeworm acquired from eating undercooked pork?&#10;A) Dipylidium spp.&#10;B) Echinococcus granulosus&#10;C) Taenia saginata&#10;D) Taenia solium&#10;E) Trichinella spiralis

Accepted Answer

If you answered Trichinella spiralis, you fell for a typical testing "bait and switch." T. spiralis is the pork roundworm and Taenia solium is the pork tapeworm. Dipylidium caninum is the common tapeworm of both cats and dogs. It may be transmitted by ingestion of fleas harboring cysticercoid larvae. Transmission to humans usually occurs when crushed fleas harboring the disease are transmitted from a pet when it licks a child's mouth.

Question 10

What roundworm is most likely to be transmitted by ingestion of food or water contaminated with feces?&#10;A) Ascaris lumbricoides&#10;B) Enterobius vermicularis&#10;C) Necator americanus&#10;D) Taenia saginata&#10;E) Toxocara canis

Accepted Answer

Ascaris lumbricoides is transmitted via the fecal-oral route. Enterobius is most likely transmitted via contaminated hands, clothing, or bedding. Necator enters by skin penetration. Taenia is not a roundworm. Toxocara is most commonly acquired from eating fecally contaminated dirt or soil.

Question 11

What roundworm is transmitted by filariform larvae that are found in the soil and penetrate the skin?&#10;A) Dracunculus medinensis&#10;B) Enterobius vermicularis&#10;C) Strongyloides stercoralis&#10;D) Taenia saginata&#10;E) Toxocara canis

Accepted Answer

The answer of What roundworm is transmitted by filariform larvae...

Question 12

How is Clonorchis sinensis (Chinese liver fluke) most likely transmitted to humans?&#10;A) Fish ingestion&#10;B) Mosquito bite&#10;C) Swimming or water contact&#10;D) Rare beef ingestion&#10;E) Mango fly (Chrysops)

Accepted Answer

The answer of How is Clonorchis sinensis (Chinese liver fluke)...

Question 13

A 48-year-old subsistence farmer from rural Brazil dies of heart failure. His autopsy shows a greatly enlarged heart. What was the vector for the most likely infectious agent that may have been responsible for his death?

A) Ixodes tick
B) Mosquito
C) Reduviid bug
D) Sandfly
E) Tsetse fly

Accepted Answer

The answer of A 48-year-old subsistence farmer from rural Brazil...

Question 14

A 16-year-old man who recently returned from camping in Canada presents with fatty diarrhea and acute abdominal pain following many meals. How does the most likely agent cause the diarrhea?&#10;A) Coinfection with bacteria&#10;B) Enterotoxin production&#10;C) Suction disk attachment&#10;D) Tissue invasion leading to an inflammatory response and prostaglandin production

Accepted Answer

The answer of A 16-year-old man who recently returned from...

Question 15

Which of the following protozoans is transmitted primarily by the motile trophozoite form?&#10;A) Balantidium coli&#10;B) Entamoeba histolytica&#10;C) Giardia lamblia&#10;D) Taenia solium&#10;E) Trichomonas vaginalis

Accepted Answer

The answer of Which of the following protozoans is transmitted...

Deck 8: Parasitic Diseases