A 45-year-old woman comes to the emergency department due to 2 days of fever, chills, malaise, and fatigue. The patient returned from an African jungle safari 3 weeks ago. She received mefloquine chemoprophylaxis during the travel, which she stopped taking upon arrival in the United States. Temperature is 38.9 C (102 F), blood pressure is 122/68 mm Hg, pulse is 110/min, and respirations are 20/min. Physical examination shows mucosal pallor. Laboratory results reveal mild anemia and thrombocytopenia. Peripheral blood smear shows intraerythrocytic Plasmodium falciparum. Which of the following is the most likely underlying cause of this patient's infection?

Question

A 45-year-old woman comes to the emergency department due to 2 days of fever, chills, malaise, and fatigue.  The patient returned from an African jungle safari 3 weeks ago.  She received mefloquine chemoprophylaxis during the travel, which she stopped taking upon arrival in the United States.  Temperature is 38.9 C (102 F), blood pressure is 122/68 mm Hg, pulse is 110/min, and respirations are 20/min.  Physical examination shows mucosal pallor.  Laboratory results reveal mild anemia and thrombocytopenia.  Peripheral blood smear shows intraerythrocytic Plasmodium falciparum.  Which of the following is the most likely underlying cause of this patient's infection?

Quizplus · Accepted Answer

11ec160b_3874_746d_9249_73aa939c2ce9_MD0001_00 Travelers to malaria-endemic regions should be counseled on mosquito avoidance measures and given chemoprophylaxis. Mosquito avoidance strategies include staying indoors at dawn/dusk (when mosquitos are most active), wearing insect repellant, limiting exposed skin, and sleeping within insecticide-treated nets. Chemoprophylaxis targets the predominant species of the region and takes into account the presence of drug resistance. In Africa, where chloroquine-resistant Plasmodium falciparum is endemic, common chemoprophylaxis regimens include atovaquone-proguanil, doxycycline, and mefloquine. Mefloquine is a schizonticide that actively destroys replicating parasites within red blood cells. However, it is inactivated in the liver and has no efficacy against hepatic schizonts. Therefore, patients must receive mefloquine chemoprophylaxis for 4 weeks upon return to ensure that parasites released from the liver are destroyed when they infect red blood cells (liver schizonts rupture over 8-30 days). Individuals who do not take mefloquine upon return (as in this case) are at risk for hepatic schizont release and subsequent red cell infection, leading to symptomatic malaria. (Choice A) Malaria undergoes asexual reproduction in humans. However, a minority of circulating merozoites differentiate into male and female gametocytes that can be passed to feeding Anopheles mosquitos to continue their replicative cycle (malaria undergoes sexual reproduction in the midgut of the mosquito). Gametocytes do not undergo sexual reproduction in humans and do not cause symptoms. (Choice B) Cases of P falciparum in Africa are usually resistant to chloroquine. Therefore, alternate agents (eg, mefloquine) are given for chemoprophylaxis. Cross-resistance between classes of medications does not typically occur. (Choice C) Malaria has been eradicated from the United States; therefore, individuals who develop malaria in the United States were infected while in other countries. This patient continued prophylaxis during the duration of her travels but ceased prophylaxis upon her return, which allowed developing hepatic schizonts to infect red blood cells and cause malaria. (Choice E) P ovale and P vivax have a dormant hepatic phase (hypnozoite) that may reactivate several months after return from an endemic region (if not treated with primaquine). In contrast, P falciparum does not have a dormant hepatic phase; it matures in (and is released from) the liver over 8-30 days. Educational objective: Mefloquine chemoprophylaxis for malaria must be continued for 4 weeks after return from an endemic region to ensure the elimination of hepatic schizonts (which develop in the liver over 8-30 days).

A 45-Year-Old Woman Comes to the Emergency Department Due to 2