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The Park: Malaria 1/2

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In this section advise is offered on malaria as it is present in the Kruger National Park.

Malaria
Malaria, disease of animals, especially birds, monkeys, and humans, caused by infection by protozoans of the genus Plasmodium and characterized by chills and intermittent fever. The causative organisms of human malaria are transmitted by the bite of about 60 species of mosquitoes in the genus Anopheles. The disease may occur in subtropical and tropical regions in almost all parts of the world as well as in other temperature areas. With the advent of control programs based on the use of residual insecticides, the distribution of malaria changed rapidly. Since 1950 malaria has been eliminated from almost all of Europe and from large areas in Central and South America. It remains a major problem in parts of Africa and in southeastern Asia. About 100 million cases of human malaria develop each year; about 1 percent are fatal.

Malaria in humans
Human malaria occurs in four forms, each caused by a different species of parasite. In each form, the symptoms usually are chills, fever, and sweating. In untreated cases, these attacks recur periodically. The mildest form of malaria is benign tertian malaria, caused by Plasmodium vivax, in which the fever may occur about every second day after the initial attack (which may occur within two weeks after infection). Jungle fever, malignant tertian malaria, or estivo-autumnal malaria, caused by Plasmodium falciparum, is responsible for most of the deaths from malaria. The organisms in this form of the disease often block the blood vessels of the brain, producing coma, delirium, and finally death.

Quartan malaria, caused by Plasmodium malariae, has a longer incubation period than either tertian malaria or jungle fever; the first attack does not appear until 18 to 40 days after infection. The attacks recur about every third day. The fourth and rarest form of the disease, caused by Plasmodium ovale, is similar to benign tertian malaria. In all forms of the disease, periodic fevers may be less regularly spaced in some people. During the incubation period of malaria, the protozoan grows within cells in the liver; a few days before the first attack, the organisms invade the red blood cells, which they destroy in the course of their development, producing the typical febrile attack.

History
Since 1638 malaria has been treated with an extract from the bark of the cinchona tree, known as quinine. Quinine, which is somewhat toxic, suppresses the growth of protozoans within the bloodstream. In 1930, German chemists synthesized Atabrine, which is more effective than quinine and less toxic. A new drug, chloroquine, that became available at the end of World War II in 1945, was found to be capable of preventing and curing jungle fever completely and to be much more effective in suppressing the other forms of malaria than Atabrine or quinine. It also had a much lower toxicity than any of the earlier drugs and was effective in less frequent doses. Recently, strains of Plasmodium falciparum, the organism that causes jungle fever, have shown resistance to chloroquine and other synthetic anti-malaria drugs. These strains are encountered most frequently in Vietnam, and also in the Malay Peninsula, Africa, and South America.

Quinine is still the agent used against Plasmodium falciparum strains resistant to synthetics. In addition to the occurrence of strains of drug-resistant parasites, the fact that some vector mosquitoes (Anophelines) have become resistant to insecticides such as DDT has led to an upsurge of malaria in certain tropical countries. As a result, malaria has increased among American and Western European travellers to Asia and Central America and among refugees from these areas. Currently, work is progressing on the development of a malaria vaccine. Several vaccine candidates are now undergoing clinical trials for safety and effectiveness in human volunteers, and scientists look forward to having a vaccine for general distribution.

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