Malaria is a highly infectious disease transmitted from human to human by mosquitoes. Coined from the Italian for "bad air," this illness was originally thought to be caused by exposure to swampy air. When the relationship between the mosquito population and the transmission of the disease was finally recognized, controlling its spread became much easier.
Almost unknown in the US and Europe, malaria is more prevalent in tropical climates, where children and pregnant women are more at risk. Symptoms are fever, joint pain, shivering, vomiting, and anemia, which can appear months or even years after initially contracting the infection. The best way to deal with the disease is to prevent mosquito bites. Preventative measures like using DEET and other insect repellents, covering one's bed with mosquito-netting in the tropics, and wearing long sleeves are all recommended.
Malaria is diagnosed through microscopic examination of the blood cells. Once a patient is diagnosed, a variety of drugs can be helpful. Quinine, distilled from the bark of a South American tree, the cinchona, was an early drug that both treated and protected against contracting the parasite that causes the illness. It is still used against variants that have developed immunity to more modern drugs. It is of historical interest that quinine is the "tonic" ingredient in tonic water, which helps to explain the popularity of gin and tonic drinks in the tropics.
Sickle cell anemia, a genetic blood disease, is a caused by a mutation that evolved in humans living in high malaria risk areas. A person who inherits the mutation from "carrier" parents will have the chronic disease, which periodically flares up and causes bouts of extreme pain. Those who only receive one copy of the mutated gene, however, have an increased resistance to malaria. This resistance for some outweighed the painful disease in others, and the mutation prospered in parts of the tropics.