Plasmodium knowlesi

Plasmodium knowlesi is a protozoan parasite of the genus Plasmodium. Plasmodium knowlesi was originally identified as malaria in macaques in Malaysia. Although it was known since the 1930s that even people can be infected with the way was clear in 2004 that the parasite is a serious pathogen. Plasmodium knowlesi is transmitted as other malaria by Anopheles mosquitoes. The distribution area is limited to Southeast Asia.

Discovery and description

Plasmodium knowlesi malaria was originally identified as a pathogen in long-tailed macaques from Singapore. The name is Robert Knowles (1883-1936) of the School of Tropical Medicine and Hygiene in Calcutta are honored who has contributed significantly to the early exploration of the Makakenmalaria.

Microscopically, trophozoites, schizonts and gametocytes of P. knowlesi indistinguishable from Plasmodium malariae in the blood smear. This can lead to dangerous misdiagnosis, as P. malariae is considered relatively benign pathogen. In contrast to P. malariae, the number of parasites in the blood in high knowlesi infections with P. and there are reports of severe disease with death. A secure differentiation of parasites requires a DNA analysis.

Plasmodium knowlesi is classified as most other primates infecting plasmodia in the subgenus Plasmodium. A phylogenetic analysis, the gene sequences of Plasmodium for four different genes have been investigated placed in close proximity to P.knowlesi Plasmodium vivax. This is also supported by comparisons of the fully sequenced genomes of both species.

Distribution and host animals

The distribution of Plasmodium knowlesi for is limited to Southeast Asia. Focuses on Borneo and the Malay Peninsula, but there are also reports of cases in Thailand, Myanmar and the Philippines. In some hospitals in Sarawak on Borneo P. knowlesi is the most commonly diagnosed malaria in humans.

The most important reservoir host for Plasmodium knowlesi are long-tailed macaques, but also the Southern Pig- called as a natural host. Experimental infections in closely related rhesus monkeys lead to fulminant disease. Also a number of other species of monkeys are susceptible to infection.

Only mosquitoes of the Anopheles leucosphyrus group can be infected with P. knowlesi and come as vectors in question. Anophleles latens, a predominantly living in forests and marginal areas type, was identified in Sarawak as a natural carrier. On the Malay Peninsula Anopheles hackeri considered as a natural vector. Transmission by mosquitoes from person to person are possible in principle, independent of monkeys reservoir cycles of infection but are limited by the presence of suitable vectors; the known mosquitoes are hard to find in settlements. The disease in humans is thus considered as a zoonosis.

Life cycle

The life cycle of P. knowlesi is similar to the other plasmodia substantially. The parasite shows an obligate host alternation. The sporozoites enter by infected mosquitoes in the bloodstream of the monkeys or people migrate from there to the liver and invade hepatocytes one in which they reproduce asexually. The incubation period of the liver phase is only five to six days in monkeys.

The Leberschizonten produce merozoites, which are released and infect red blood cells, where another asexual reproduction takes place. The generation time for the proliferation in the erythrocytes is approximately 24 hours, and is thus shorter than that in any other malaria parasites of primates. By synchronizing the development, it comes at the end of each cycle of propagation to a massive release of new parasites, which is connected with a daily fever.

A few plasmodia developing in the erythrocytes to generation forms. This microgametocyte and macrogametocyte can be taken up by mosquitoes during a blood meal, and in the intestines of the insect a new development cycle in motion. After a fusion of the gametes new sporozoites are formed in the intestine, which migrate to the salivary glands, from where they can be transferred to a new host. The development time in the mosquito is approximately 12 to 15 days.

Resting forms of the parasite that could lead to relapse, there is not in P. knowlesi.