– An infectious disease transmitted by a mosquito bite and characterized by fever, sweats, and chills.
Causes and Incidence
Malaria is caused by four species of protozoan parasites: Plasmodium vivax, P. falciparum, P. malariae, and P. ovale. Infection occurs through the bite of an infected mosquito or by contact with blood products from an infected individual. It is estimated that there are more than 100 million cases of malaria worldwide each year; 1 million people die of the disease annually in Africa alone. Most endemic areas are in the tropics, and underdeveloped countries are particularly hard hit. Relatively few cases are reported in the United States annually, and most involve travelers to endemic regions.
A mosquito carrier bites a human host and injects the sporozoites, which reside and multiply in the parenchymal cells of the liver. After a maturation period averaging 2 to 4 weeks, merozoites are released and invade the erythrocytes. The infected erythrocytes rupture and release merozoites, pyrogens, and toxins, which cause hemolysis, sluggish blood flow in the capillaries, and adherence of infected erythrocytes to venous walls, obstructing blood flow, increasing the permeability of the capillaries, and causing tissue extravasation, particularly in the brain and gastrointestinal system.
The incubation period is followed by a 2- to 3-day prodromal period marked by low-grade fever, malaise, headache, joint aches, and chills similar to the flu and often misdiagnosed and treated as such. A paroxysmal pattern is then established, beginning with a shaking chill and followed by fever and sweats. After the fever and sweats (usually lasting 1 to 8 hours), the person feels well until the next chill begins. One cycle ranges from 20 to 72 hours, depending on the parasite involved.
Chronic malaria with accompanying parasitemia may occur in partially immune individuals in hyperendemic areas. It is characterized by recurring symptoms resembling a mild, short attack of acute malaria. Blackwater fever is a rare complication characterized by severe hemolytic anemia and renal failure. Uremia and renal failure are common complications. Cerebral malaria causes seizure, psychosis, and coma. Pulmonary edema and splenic rupture are also seen. Untreated malaria caused by P. falciparum has a 20% mortality rate.
A physical evaluation revealing the paroxysmal pattern and an enlarged spleen plus a history of exposure to an endemic area within the year is significant. A blood smear that isolates the parasite provides the definitive diagnosis.
Antimalarial drugs for acute attacks and as prophylaxis if traveling to endemic areas; vaccines are experimental.
Individual prophylaxis includes insect repellent, covering of skin, use of mosquito netting for bed, and avoidance of outdoors at night when in endemic areas; community prophylaxis includes control of mosquito breeding grounds and protection of the blood supply.