malaria

malaria infectious parasitic disease that can be either acute or chronic and is frequently recurrent. Malaria is common in Africa, Central and South America, the Mediterranean countries, Asia, and many of the Pacific islands. In the United States it was found in the South and less frequently in the northern and western parts of the country.

The primary causative organism, Plasmodium falciparum, requires both the Anopheles mosquito and humans to complete its life cycle: sexual reproduction of the protozoan occurs in the mosquito; an immature form is then transmitted to the human via the bite of the mosquito. In a person the parasite goes to the liver, replicates, and moves into the bloodstream, where it attacks red blood cells for their hemoglobin. Some of the plasmodia become sexually mature and are transmitted back to another biting mosquito. Three other Plasmodium species also infect humans.

Symptoms

At the onset of malaria, bouts of chills (ague) and fever lasting several hours and occurring every three or four days are the usual symptoms. If the disease is not treated, the spleen and the liver become enlarged, anemia develops, and jaundice appears. Death may occur from general debility, anemia, or clogging of the vessels of cerebral tissues by affected red blood cells. Cerebral malaria is most commonly seen in infants, pregnant women, and nonimmune travelers to endemic areas.

Immune Response

P. falciparum creates protein knobs on the surfaces of the red blood cells it attacks. These knobs attach the cell to the lining of the blood vessel, preventing its removal to the spleen for destruction. The parasite slows detection by the immune system by changing the makeup of the knobs periodically, substituting or rearranging its 150 "var" (variability) genes, a strategy unique to malaria. A pattern of remission and relapse results as the immune system learns each new "code" only to have it again changed. Patients with malaria gradually do develop immunity that modifies the course of the disease, but this immunity has a degree of strain specificity.

Treatment and Control

The bark of the cinchona and its product, quinine , have been used in the treatment of malaria for centuries. After World War II, they were largely replaced by the synthetic analog chloroquine. The use of chloroquine, in addition to the use of DDT for mosquito control, was expected to eradicate the disease, but a World Health Organization campaign (1955-69) to eradicate the disease globally (by controlling mosquitoes long enough to allow the human population to become disease free) proved unsuccessful. Despite that, spraying successfully eradicated the disease in some areas (Sardinia, Japan, and Taiwan).

In the 1960s several strains of the malarial parasite developed resistance to chloroquine. This, plus the growing immunity of mosquitoes to insecticides, has caused malaria to become one the of world's leading re-emerging infectious diseases, infecting an estimated 300 million people a year and killing more than a million. Mefloquine may be used in areas where the disease has become highly resistant to chloroquine, but some strains are now resistant to it and other drugs. Artemisinin (derived from sweet wormwood) in combination with other drugs is now in many cases the preferred treat for resistant strains. Amodiaquine in combination with sulfadoxine and pyrimethamine has also been shown to be effective, and malarone (atovaquone and proguanil) also is used for resistant strains. Vaccines against malaria are still experimental. Spraying is still used to control malaria-transmitting mosquitoes, but fish that feed on mosquito larva also have been employed.

malaria fever formerly supposed to be caused by exhalations from marshy places. XVIII. — It. mal'aria for mala aria ‘bad AIR’; cf. MAL-.

Malaria. A mosquito‐borne disease once attributed to foul air emanating from swamps, malaria came to America in the bodies of both African and European colonists during the seventeenth century.While at times it appeared in states as far north as New Hampshire and Minnesota, it was a particular scourge of the South. The ravages of the most severe type of malaria (falciparum) influenced the choice of African slave labor for plantations in Carolina and Virginia, because African workers tolerated the disease and remained at work after European field hands had become incapacitated. Malaria also played an important role on the early frontier, since the principal form of transportation, river travel, dictated prolonged exposure to wetland areas.

By the twentieth century malaria, for a variety of environmental reasons, had retreated largely to the southern states. British physician Ronald Ross's discovery in 1897 that the anopheles mosquito transmitted malaria prompted southern towns in the early twentieth century to the destruction of mosquito larvae. A similar strategy of eradication eliminated the scourge of malaria from the Panama Canal Zone. Still, rural malaria persisted in the South because the cost per capita for malaria control in the sparsely populated countryside was so high. The federal government supported antimosquito work in the South, including drainage programs in the 1930s and extensive spraying of the pesticide DDT after 1945. These measures, along with the migration of susceptible sharecroppers from the rural South into disease‐free cities and towns, contributed to the disappearance of indigenous malaria from the United States by 1950.
See also Public Health; Sickle‐Cell Anemia; Slavery: Development and Expansion of Slavery.

Bibliography

Erwin H. Ackerknecht , Malaria in the Upper Mississippi Valley, 1760–1900, 1945.
Margaret Humphreys , Kicking a Dying Dog: DDT and the Demise of Malaria in the American South, 1942–1952, Isis 87 (1996): 1–17.

Margaret Humphreys