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Malaria must be considered in any person who has traveled to the tropics and presents with an unexplained febrile illness. Five species of the protozoan Plasmodium infect humans: P falciparum, P vivax, P ovale, P malariae, and P knowlesi. The organism is transmitted by the anopheline mosquito bite and travels hematogenously first to the liver, where asexual reproduction occurs (exoerythrocytic stage). The liver cell ruptures, releasing merozoites that invade erythrocytes, multiply, and cause hemolysis (erythrocytic stage). Malaria also may be transmitted by blood transfusion or passed transplacentally from mother to fetus.

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Malaria transmission occurs in large areas of Central and South America, the Caribbean, sub-Saharan Africa, the Indian subcontinent, Southeast Asia, the Middle East, and Oceania (New Guinea, Solomon Islands, etc). More than 50% of all the cases of malaria in the United States, including most cases due to P falciparum, arise from travel to sub-Saharan Africa. Resistance of P falciparum to chloroquine and other drugs continues to spread (see Table 95-1). Strains of P vivax with chloroquine resistance have been identified. The Centers for Disease Control and Prevention (CDC) has a malaria hotline: 770-488-7788 M-F, 8 am to 4:30 pm EST, and 770-488-7100 after hours, weekends and holidays. Alternatively, the CDC website can be accessed at http://www.cdc.gov/malaria/ for information on resistance patterns in various countries and information on malaria prophylaxis and treatment. When in doubt, chloroquine resistance for initial treatment should be assumed.

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Table 95-1 Geographic Distribution of Malaria, Including Resistant Strains
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The incubation period ranges from 1 to 4 weeks. Partial chemoprophylaxis or incomplete immunity can prolong the incubation period to months or even years. Initially malaria manifests with nonspecific fever and malaise, then progresses to chills and high grade fevers; frequent symptoms include headache, myalgia, arthralgia, cough, abdominal pain, nausea, and diarrhea. The patient may have tachycardia, orthostatic dizziness, and extreme weakness. Classically, cycles of fever and chills followed by profuse diaphoresis and exhaustion occur at regular intervals, reflecting hemolysis of infected erythrocytes.

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Physical examination findings are typically nonspecific. During a febrile paroxysm, most patients appear acutely ill, ...

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