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Old 06-29-2011
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Microbiology most likely parasite!

One week following a visit to the woods along an Eastern seaboard beach,
a 50-year-old woman develops fever, headache, chills, and fatigue. A blood
smear demonstrates protozoa within erythrocytes. Which of the following is
the most likely pathogen?

A. Babesia microti
B. Leishmania donovania
C. Plasmodium falciparum
D. Plasmodium vivax
E. Trypanosoma cruzi
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Old 06-29-2011
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Quote:
Originally Posted by earthpole View Post
One week following a visit to the woods along an Eastern seaboard beach,
a 50-year-old woman develops fever, headache, chills, and fatigue. A blood
smear demonstrates protozoa within erythrocytes. Which of the following is
the most likely pathogen?

A. Babesia microti
B. Leishmania donovania
C. Plasmodium falciparum
D. Plasmodium vivax
E. Trypanosoma cruzi
answer is A
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Old 06-29-2011
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The answer is A.

The combination of a one week incubation period, the Eastern seaboard clue, and the intra-erythrocyte parasites strongly suggest Babesia microti as the infecting organism. The clinical disease is called babesiosis. The infecting protozoan is related to Plasmodium and is transmitted by the bite of the Ixodes dammini tick. Occasional cases have been transmitted by blood transfusions. Most patients are asymptomatic; symptomatic cases in reasonably healthy individuals have the features listed in the question stem. Rare severe cases, which may be fatal, may develop in severely debilitated or asplenic individuals and can be accompanied by severe hemolysis (up to 30% of RBCs may have the parasites) with subsequent hemoglobinuria, hemolysis, and renal failure.
Leishmania donovania (choice B) is an intracellular tissue protozoan, not a blood protozoan.
Plasmodium falciparum (choice C) and Plasmodium vivax (choice D) are malarial parasites not encountered on the Eastern seaboard.
Trypanosoma cruzi (choice E) is an intracellular tissue protozoan, and does not infect blood cells.
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