Is the malaria parasite winning the war against people? The microscopic organism that is transmitted by a biting mosquito is staging a major comeback in Southeast Asia, South America and especially in Africa.

"There's no getting around it," says Duane Gubler, director of the Division of Vector-Borne Infectious Diseases for the Centers for Disease Control, "we're losing ground fast."

Kent Campbell, the CDC's specialist on parasitic diseases, says that the most lethal form of malaria is caused by Plasmodium falsiparum, an organism "with the very troubling capacity to develop resistance to anything we can devise to try to kill it."

Chloroquine, a drug developed in the late 1940s, worked well when taken as a preventative against the one-celled parasite for about 15 years. Then, almost simultaneously in the most affected regions, drug-resistant cases began occurring. Today, although it is still useful as a treatment in very high doses, chloroquine is of little help in preventing malaria, which causes shaking chills, high fever and headache and can be fatal.

A new drug, mefloquine (brand name Lariam), has been found useful as a prophylactic, but it is neither as effective as chloroquine was nor as safe.

Pregnant women, people taking such heart drugs as beta blockers or calcium channel blockers and those with a history of epilepsy or psychiatric disorders are cautioned not to take Mefloquine. It is not approved for children.

Another anti-malarial called Paludrine is currently being reviewed by the Food and Drug Administration. Paludrine is approved in England and is available in most of Europe, Canada and in parts of Africa. According to the American Society of Tropical Medicine, it is the best tolerated of all anti-malarial drugs.