Malaria is caused by protozoan parasites of the genus Plasmodium – single-celled organisms that cannot survive outside of their host(s).
Plasmodium falciparum is responsible for the majority of malaria deaths globally and is the most prevalent species in sub-Saharan Africa. The remaining species are not typically as life threatening as P. falciparum.
Plasmodium vivax, is the second most significant species and is prevalent in Southeast Asia and Latin America. P. vivax and Plasmodium ovale have the added complication of a dormant liver stage, which can be reactivated in the absence of a mosquito bite, leading to clinical symptoms.
P. ovale and Plasmodium malariae represent only a small percentage of infections.
A fifth species Plasmodium knowlesi– a species that infects primates – has led to human malaria, but the exact mode of transmission remains unclear.