Malaria

Malaria is an infectious disease caused by single-celled parasites of the genus Plasmodium. Five species infect humans: P. falciparum causes most deaths and dominates in Africa, while P. vivax is more common in many other regions. The parasites spread through the bites of infected female Anopheles mosquitoes, and occasionally through transfusions or from mother to baby. Malaria causes hundreds of millions of illnesses and over half a million deaths a year, mostly among young children in sub-Saharan Africa.

A mosquito injects sporozoites, which travel to the liver and multiply there for about a week before releasing merozoites that invade red blood cells. Repeated cycles of growth and bursting of red cells cause the waves of fever, chills and sweating typical of malaria, along with anemia. P. falciparum also makes infected cells stick inside small blood vessels, which can cause severe malaria with coma and organ failure. P. vivax and P. ovale can rest in the liver as dormant hypnozoites and cause relapses months later. Some parasites become gametocytes, which a biting mosquito takes up to continue the cycle.

Diagnosis uses stained blood smears or rapid antigen tests. Artemisinin-based combination therapies are the main treatment for falciparum malaria, and prevention relies on insecticide-treated bed nets, indoor spraying, preventive medicines and, since 2021, vaccines for young children.