It responds well to modern drugs, but after recovery from the acute attack, it tends to be chronic with occasional relapses. It is endemic to parts of Africa, Asia, and Central and South America, and is estimated to occur at the rate of 100 million cases each year worldwide. It is one of the world's major causes of death, causing about a million deaths a year, and the number is increasing. Epidemics usually occur in areas where mosquitoes persist in large numbers and the parasite is introduced into a region populated with persons who are not immune to malaria.
Acute cases occur when nonimmune persons travel to regions where the disease is endemic.
A worldwide cooperative program begun in the 1960s has met with limited success. Some difficulties encountered have been resistance of mosquitoes to insecticides, insufficient funding in some underdeveloped countries, resistance of plasmodia to antimalarial drugs, and the discovery that malaria in monkeys can be transmitted to man. In view of these difficulties recent efforts have been toward malaria control rather than eradication. C AUSE . Malaria is caused by a protozoan parasite, Plasmodium, which is carried by the Anopheles mosquito.