Malaria

• Most common cause of fever in recent travelers (20%)
• Malaria is present in 40% of patients from Africa with fever (contrast with dengue, which is present in only 1%)
• 90% of falciparum is acquired in sub-Saharan Africa - given high degree of parasitemia, 90% of patients have symptoms within one month
• 70% of vivax/ovale is acquired in Asia/S. America – only 50% have symptoms within one month
• Life cycle:
• Anopheles mosquito bite à sporozoites travel to liver à form tissue schizonts
• Tissue schizonts rupture à release merozoites into bloodstream, which invade RBCs à mature to trophozoites (ring forms) à form RBC schizonts à rupture and invade additional RBCs, or mature into gametocytes
• Pathogenesis:
• Increased glycolysis, leading to hypoglycemia and lactic acidosis
• Reduction in RBC membrane deformity, resulting in hemolysis, anemia, splenomegaly
• RBCs become sticky and adhere to microvasculature, leading to end organ hypoperfusion
• Prevention:
• Mosquito prevention: avoiding outdoors at dusk/dawn, repellant, bed nets, screened/air conditioned rooms
• Chemoprophylaxis: initiated before travel, and continued after return
• Atovaquone-proguanil: expensive, daily dosing, continued for one week after return
• Mefloquine: weekly dosing, continued for 4 weeks after return; psychiatric side effects can be troubling to patients
• Doxycycline: daily dosing, continued for  4 weeks after return; photosensitization may be issue in travelers
• Chloroquine: weekly dosing, continued for 4 weeks after return
• Primaquine: for vivax and ovale, has activity against liver hypnozoites (terminal prophylaxis)
• Symptoms:
• Uncomplicated: fever without localizing symptoms (though up to 40% afebrile at presentation), headache, cough, GI complaints, arthralgias, myalgias
• Complicated: in patients with a high burden of parasitemia (>5%), end organ dysfunction may be present
• Neuro: AMS, seizures
• CV: hypotension
• Pul: ARDS
• Renal: AKI, hemoglobinuria, lactic acidosis
• GI: liver failure
• Heme: DIC, anemia
• Endo: hypoglycemia
• Diagnosis:
• Physical exam: splenomegaly, jaundice
• Labs: thrombocytopenia, hyperbilirubinemia
• LP: mildly elevated protein and cell count
• Microscopy
• Thick smear: more sensitive
• Thin smear: allows for speciation and quantitation of parasitic load
• ·Characteristic findings of falciparum are thin ring forms found at periphery of RBCs, multiple rings/cell, rings with “double dots” (headphones), and banana-shaped gametocytes
• If smears initially negative, should be repeated every 6-12 hours for two days, given cyclical nature of parasitemia
• Rapid diagnostic tests: utilize specific malarial antigens including plasmodium LDH (“Binax” is the only RDT that is currently FDA approved); limitations include inability to quantify parastitemia, limited sensitivity for particular species  
• Treatment:
• Uncomplicated:
• Chloroquine (central America west of Panama Canal, Middle East, Haiti, Dominican Republic)
• Chloroquine-resistant regions:
• ·Artemisinin combination therapy
• Atovaquone-proguanil
• Quinine
• Mefloquine (high resistance rates in SE Asia)
• Complicated: requires parenteral therapy with quinidine or artesunate
  

(Christopher Woo MD, 1/20/11)

(Victoria Kelly MD, 9/9/10)