There are over 100 million species of Plasmodium that is known to infect animals such as reptiles, birds, and mammals. Four species of Plasmodium is known to infect humans in nature. In addition, there are some additional species which are able to infect humans exceptionally or under experimental conditions such as on that infects macaques and has been recognised to be a cause of zoonotic malaria in humans.
P. falciparum: found worldwide in tropical and subtropical areas. Approximately 1 million people are killed by this species, especially in Africa where it predominates. P. falciparum can cause severe malaria as it multiplies rapidly in the blood thus causing anemia. The infected parasites are able to clog small blood vessels.
P. vivax: found mostly in Asia, Latin America, and in some parts of Africa. As Asia has one of the largest population densities, P. vivax is probably the most prevalent human malaria parasite. It has dormant liver stages that can activate and invade the blood several months or years after the infecting mosquito bite.
P. ovale: found mostly in Africa (especially West Africa) and the islands of the western Pacific. It is biologically and morphologically very similar to P. vivax; however, it can infect individuals who are negative for the Duffy blood group, which is the case for many residents of sub-Saharan Africa. RBCs that lack the Duffy antigens are relatively resistant to invasion by P. vivax. This explains the greater prevalence of P. ovale in most of Africa.
P. malariae: found worldwide and is the only human malaria parasite species that has a quartan cycle. If untreated, it can cause a long-lasting, chronic infection that in some cases can last a lifetime, and complications such as the nephrotic syndrome.
P. knowlesi: found throughout Southeast Asia as a natural pathogen of long-tailed and pig-tailed macaques. It has shown to be a significant cause of zoonotic malaria in that region. P. knowlesi’s rapid 24-hour replication cycle causes severe infections, even fatal.
(photo:Â http://www.cdc.gov/dpdx/)
(Centers for Disease Control and Prevention, 2015)
(National Center for Biotechnology Information, U.S. National Library of Medicine, 2005)