Plasmodium species and their distribution
There are four species of Plasmodium that cause human malaria:
Widespread species:Plasmodium falciparum Plasmodium vivax
Less widespread species: Plasmodium malariae Plasmodium ovale
Subdivision of Plasmodium
The genus Plasmodium is subdivided into the subgenus Laverania and the subgenus of the same name, i.e. Plasmodium. P.falciparum belongs to the subgenus Laverania and P. vivax, P. ovale and P. malariae belong to the subgenus Plasmodium.
P. falciparum is found mainly in the hotter and more humid regions of the world. It is the main species found in tropical and subtropical Africa and parts of Central America and South America, Bangladesh, Pakistan, Afghanistan, Nepal, Sri Lanka, South East Asia, Indonesia, Philippines, Haiti, Solomon Islands, Papua New Guinea and many islands in Melanesia. It also occurs in parts of India, the Middle East, and eastern Mediterranean. Varieties of Plasmodium falciparum The species Plasmodium falciparum contains several ‘varieties’ which show differences in geographical distribution, vector susceptibility, human infection pattern, drug susceptibility, morphology and antigenic composition.
P. vivax is capable of developing in mosquitoes at lower temperatures than P. falciparum and therefore has a wider distribution in temperate and sub-tropical areas. P. vivax is the main Plasmodium species in South America (occurring as far south as northern Argentina), Mexico, the Middle East, northern Africa, India, Pakistan, Sri Lanka, Papua New Guinea and the Solomon Islands. It is also found in parts of South East Asia, Indonesia, Philippines, Madagascar, tropical and subtropical Africa, Korea, and China. Strains of Plasmodium vivax The species P. vivax contains many strains which show differences in incubation time, relapsing pattern, morphology, number of parasites in red cells, and response to antimalarials.
P. malariae has a much lower prevalence than P. falciparum and P. vivax. It is found in tropical and subtropical regions. In tropical Africa it accounts for up to 25% of Plasmodium infections. It is also present in Guyana, India, Sri Lanka and Malaysia. In these countries it accounts for less than 10% of Plasmodium infections. Plasmodium knowlesi: Human infections with P. knowlesi, a species that naturally infects monkeys (macaques), have been reported from Malaysia and Thailand. Morphologically P. knowlesi resembles P.malariae but unlike P.malariae, parasite numbers have been reported as high and clinical symptoms more severe.20
P. ovale has a low prevalence. It is found in West Africa where it accounts for up to 10% of malaria infections and has also been reported from other parts of Africa, and from the Philippines, Indonesia, China, and parts of the Far East, South East Asia, and South America.
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