A bite from a parasite-infected mosquito causes malaria. There are five species of Plasmodium(P.) parasites that infect people.

Infection with P. falciparum

• P. falciparum is found mostly in the tropics and subtropics (near the equator).
• Infection with P. falciparum can lead to life-threatening complications after the first few days.
• P. falciparum is often resistant to a popular antimalarial medicine (chloroquine) and needs treatment with other medicines.

Infection with P. vivax, P. malariae, P. ovale, or P. knowlesi

• P. vivax and P. malariae occur all over the tropical regions of the world. P. ovale is found in western Africa, and P. knowlesi is found in Southeast Asia.
• Infection with P. vivax, P. malariae, or P. ovale is usually not life-threatening, and a person may recover in a month without treatment. But infection with P. knowlesi may be fatal.
• P. vivax, P. malariae, P. ovale, and P. knowlesi are generally not as drug-resistant as P. falciparum.
• P. vivax P. ovale, and P. knowlesi may stay in the liver, requiring further treatment with medicine to prevent relapses.

How the disease spreads

Malaria is spread when an infected Anopheles mosquito bites a person. This is the only type of mosquito that can spread malaria. The mosquito becomes infected by biting an infected person and drawing blood that contains the parasite. When that mosquito bites another person, that person becomes infected.

In the United States, people who develop malaria almost always got infected while traveling in parts of the world where malaria is common. For more information, see the topic Travel Health.