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

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 medication (chloroquine) and needs treatment with other medications.

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

• P. vivax and P. malariae occur all over the tropical regions of the world. P. ovale is found in western Africa.
• Infection with any of these three types of malaria usually is not life-threatening, and a person may recover in a month without treatment.
• P. vivax, P. malariae, and P. ovale generally are not as drug-resistant as P. falciparum.
• P. vivax and P. ovale 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. Only this type of mosquito 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 are nearly always found to have contracted it while traveling in parts of the world where malaria is common. For more information, see the topic Travel Health.