A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 29-year-old woman comes to the physician with high-grade fever, headache, and muscle pain. A week ago, she returned from India, where she was working with an NGO to build houses in rural areas. The patient took one dose of chloroquine one week before her trip. She also took a further dose during her trip. She has no history of a serious illness. Her temperature is 39.3°C (102.7°F), pulse is 102/min, respirations are 22/min, and blood pressure is 112/78 mm Hg. Physical examination shows jaundice. The abdomen is soft and nontender. The remainder of the examination shows no abnormalities. Her hemoglobin concentration is 10 g/dL and a blood smear shows fragmented erythrocytes and occasional ring-shaped inclusion bodies within erythrocytes. Which of the following is the most likely cause of infection in this patient?
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A
Plasmodium ovaleIncorrect. P. ovale causes relapsing tertian malaria due to hypnozoite formation, is generally milder, and rarely causes severe hemolysis or jaundice as seen here.
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B
Plasmodium falciparumCorrect. Chloroquine-resistant P. falciparum is the predominant species in India and produces severe hemolysis with intra-erythrocytic ring forms, jaundice, and high fever.
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C
Chikungunya virusIncorrect. Chikungunya causes fever and severe arthralgia after travel to South Asia but does not produce hemolytic anemia or intraerythrocytic ring forms.
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D
Hepatitis A virusIncorrect. Hepatitis A causes acute hepatitis with jaundice but not hemolysis, fragmented red cells, or ring forms on blood smear.
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E
Dengue virusIncorrect. Dengue causes high fever, retro-orbital pain, and thrombocytopenia after travel to South Asia, but produces no intra-erythrocytic ring forms on smear and does not cause classic hemolytic anemia with jaundice.
↑ Tap an answer to reveal the reasoning
Answer: B. This young woman returning from rural India presents with high fever, headache, myalgias, jaundice, anemia, and intra-erythrocytic ring-form parasites on smear — classic findings for malaria. The presence of fragmented red cells (schistocytes) signals intravascular hemolysis, and the fact that she developed disease despite chloroquine prophylaxis points to Plasmodium falciparum, which is the most common species in India and is essentially universally chloroquine-resistant in endemic areas.
P. falciparum is the most virulent species because it can parasitize erythrocytes of any age, producing high parasitemias, microvascular sequestration, intravascular hemolysis, cerebral malaria, and acute renal failure — features not typically seen with the more benign P. vivax/ovale. Treatment of severe falciparum malaria is IV artesunate.
Clinical pearl: chloroquine remains effective only for P. vivax, ovale, malariae, and a few geographic pockets; for India and most of Africa, atovaquone-proguanil, mefloquine, or doxycycline are appropriate prophylaxis. Chikungunya causes fever and arthralgia but not hemolysis or ring forms in red cells.
**Why each option:**
**A.** P. ovale causes relapsing tertian malaria due to hypnozoite formation, is generally milder, and rarely causes severe hemolysis or jaundice as seen here.
**B.** Correct. Chloroquine-resistant P. falciparum is the predominant species in India and produces severe hemolysis with intra-erythrocytic ring forms, jaundice, and high fever.
**C.** Chikungunya causes fever and severe arthralgia after travel to South Asia but does not produce hemolytic anemia or intraerythrocytic ring forms.
**D.** Hepatitis A causes acute hepatitis with jaundice but not hemolysis, fragmented red cells, or ring forms on blood smear.