Malaria

General: Once thought to be due to "bad air" ("mal" "aria"), Plasmodium sp., a protozoan, is in fact vectored by the bite of the female Anopheles mosquito (and rarely by transfusion or mother to fetus). About 90% of deaths occur in sub-Saharan Africa, primarily in young children. Rarely found in the U.S.; most infections are in sub-Saharan Africa, as well as other undeveloped areas globally. It has a complex life cycle; ....

Clinical: Highest mortality among children and pregnant women. Flu-like symptoms develop 9~14 days following bite, with some variance among species. It infects and destroys erythrocytes (after utilizing hemoglobin and other intracellular proteins), causing some degree of anemia and flu-like symptoms secondary to released RBC metabolic byproducts, and may be so abundant as to clog capillaries. It is associated with normal or reduced leukocytes, though leukocytosis may develop in terminal cases, and severe thrombocytopenia is common. The parasites exclusively use glucose as an energy source, causing host hypoglycemia and lactic acidosis. Homozygosity for sickle cell disease is relatively protective from infection.

Resistance: Generally increasing resistances worldwide. Control is often by way of insecticides and mosquito nets — prevention of infection and destruction of the vector.

Growth characteristics: Produce plasmodial histidine rich protein-2 (HRP-2) or parasite-specific lactate dehydrogenase (pLDH), present in P. falciparum (the highest and most rapid mortality) infections; these are the basis for several simple blood "dipstick" tests, which have a rare reported cross-reactivity with rheumatoid factor positive sera (up to ~6%). The levels, however, may be positively elevated for ~2wks even in the absence of viable organisms. The "gold standard" test remains the examination of thick & thin peripheral blood smears; thick distorts the morphology but increases the concentration per field. Parasites may appear distorted due to treatment, including prophylaxis. Ideally blood should be collected as patient's temperature is rising. PCR is becoming more important/common in speciation.

Common/important pathogens:

• Plasmodium falciparum (highest and most rapid mortality)
• Plasmodium malariae
• Plasmodium ovale
• Plasmodium vivax