Malaria is a protozoan (Plasmodium) infection transmitted by the biting female Anopheles mosquito. The disease affects approximately 40% of the world's population, and an estimated 50 to 70 million Western travelers are exposed to malaria infection annually. Malaria and travelers are inextricably linked since the dawn of time. Malaria owes its distribution worldwide to human travelers, and travelers are linked with the discovery, refinement, and development of several antimalarial drugs. In the year 2003 the genomes for humans, mosquito, and Plasmodium have been completed, but no malaria vaccine is available as yet.