Malaria is a highly infectious disease transmitted from human to human by mosquitoes. Coined from the Italian for 'bad air', malaria was originally thought to be caused by exposure to swampy air. When the relationship between the mosquito population and the transmission of malaria was finally recognized, controlling the spread of malaria 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. Preventive measures are those that would prevent mosquito bites. DEET and other insect repellents, covering one's bed with mosquito-netting in the tropics, wearing long sleeves and other measures to prevent mosquitoes from having access to bare skin all prevent infection.

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 malaria. It is still used against variants of malaria that have developed immunity to more modern drugs. It is of historical interest that quinine is the 'tonic' ingredient in tonic water. This 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 sickle cell anemia, a chronic disease that 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. The resistance to malaria for some outweighed the painful disease in others, and the mutation prospered in high malaria zones in the tropics.