Plasmodium knowlesi
| Plasmodium knowlesi | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Plasmodium knowlesi | ||||||||||||
| Sinton and Mulligan , 1932 |
Plasmodium knowlesi is a protozoan parasite of the genus of plasmodia . Plasmodium knowlesi was originally identified as a malaria pathogen in macaques in Malaysia. Although it had been known since the 1930s that the species could also infect humans, it was only in 2004 that it became clear that the parasite is a serious pathogen . Like other malaria pathogens, Plasmodium knowlesi istransmittedby Anopheles mosquitoes . The distribution area is limited to Southeast Asia.
Discovery and Description
Plasmodium knowlesi was originally identified as a malaria pathogen in a long-tailed macaque from Singapore. The name is said to honor Robert Knowles (1883-1936) of the School of Tropical Medicine and Hygiene in Calcutta, who contributed significantly to the early research into macaque malaria.
Microscopically, trophozoites , schizonts and gametocytes of P. knowlesi cannot be distinguished from Plasmodium malariae in the blood smear . This can lead to dangerous misdiagnosis, as P. malariae is viewed as a relatively benign pathogen. In contrast to P. malariae , the number of parasites in the blood is high in infections with P. knowlesi and there have been reports of severe disease with fatalities. A reliable differentiation of the parasites requires a DNA analysis.
Plasmodium knowlesi , like most other primates infecting Plasmodium, is classified in the subgenus Plasmodium. A phylogenetic analysis, in which the gene sequences for four different genes were examined from Plasmodium, places P. knowlesi in close proximity to Plasmodium vivax . This is also supported by comparisons of the fully sequenced genomes of both species.
Distribution and host animals
The distribution area for Plasmodium knowlesi is limited to Southeast Asia. The focus is on Borneo and the Malay Peninsula , but there have also been reports of cases in Thailand , Myanmar and the Philippines . In some hospitals in Sarawak , Borneo, P. knowlesi is the most frequently diagnosed malaria pathogen in humans.
The most important reservoir hosts for Plasmodium knowlesi are long-tailed macaques, but the southern porcupine monkey is also mentioned as a natural host. Experimental infections in the closely related rhesus monkey lead to a fulminant disease. A number of other species of monkeys can also be infected.
Only mosquitoes from the Anopheles leucosphyrus group can be infected with P. knowlesi and can be used as vectors . Anopheles latens , a species that predominantly lives in forests and peripheral areas, has been identified as a natural vector in Sarawak. Anopheles hackeri is considered a natural vector in the Malay Peninsula . Transmission by mosquitoes from person to person is possible in principle, but infection cycles independent of monkey reservoirs are limited by the presence of suitable vectors; the known mosquitoes are rarely found in settlements. The disease in humans is thus regarded as a zoonosis .
Life cycle
The life cycle of P. knowlesi is essentially similar to that of other plasmodia. The parasite shows an obligatory change of host. The sporozoites enter the bloodstream of monkeys or humans through infected mosquitoes, migrate from there to the liver and invade hepatocytes , in which they reproduce asexually. The incubation time of this liver phase is only five to six days in monkeys.
The liver schizonts produce merozoites , which are released and attack red blood cells, where further asexual reproduction takes place. The generation time for the multiplication in the erythrocytes is about 24 hours and is thus shorter than with all other malaria pathogens in primates. By synchronizing development, at the end of each reproduction cycle there is a massive release of new parasites, which is associated with a daily fever.
A few plasmodia develop into sex forms in the erythrocytes. These microgametocytes and macrogametocytes can be ingested by mosquitoes with a blood meal and start a new development cycle in the insect's intestine. After the gametes fuse, new sporozoites are formed in the intestine that migrate to the salivary gland, from where they can be transferred to a new host. The development time in the mosquito is about 12 to 15 days.
There are no resting forms of the parasite that could lead to relapses in P. knowlesi .
Individual evidence
- ↑ B. Singh, L. Kim-Sung, A. Matusop, A. Radhakrishnan, SS Shamsul, J. Cox-Singh, A. Thomas, DJ Conway: A large focus of naturally acquired Plasmodium knowlesi infections in human beings. In: Lancet. 363 (9414), Mar 27, 2004, pp. 1017-1024. PMID 15051281
- ↑ ES Martinsen, SL Perkins, JJ Schall: A three-genome phylogeny of malaria parasites (Plasmodium and closely related genera): evolution of life-history traits and host switches. In: Mol Phylogenet Evol. 47 (1), Apr 2008, pp. 261-273. PMID 18248741
- ↑ A. Pain, U. Böhme, AE Berry, K. Mungall, RD Finn, AP Jackson, T. Mourier, J. Mistry, EM Pasini, MA Aslett, S. Balasubrammaniam, K. Borgwardt, K. Brooks, C. Carret, TJ Carver, I. Cherevach, T. Chillingworth, TG Clark, MR Galinski, N. Hall, D. Harper, D. Harris, H. Hauser, A. Ivens, CS Janssen, T. Keane, N. Larke, S. Lapp, M. Marti, S. Moule, IM Meyer, D. Ormond, N. Peters, M. Sanders, S. Sanders, TJ Sargeant, M. Simmonds, F. Smith, R. Squares, S. Thurston, AR Tivey, D. Walker, B. White, E. Zuiderwijk, C. Churcher, MA Quail, AF Cowman, CM Turner, MA Rajandream, CH Kocken, AW Thomas, CI Newbold, BG Barrell, M. Berriman: The genome of the simian and human malaria parasite Plasmodium knowlesi. In: Nature. 455 (7214), Oct 9, 2008, pp. 799-803. PMID 18843368
literature
- G. Robert Coatney, William E. Collins, McWilson Warren, Peter G. Contacos: The primate malarias. US National Institute of Allergy and Infectious Diseases, Bethesda 1971, Chapter 26, p. 317 ff .: Plasmodium knowlesi
- J. Cox-Singh, B. Singh: Knowlesi malaria: newly emergent and of public health importance? In: Trends Parasitol. 24 (9), Sep 2008, pp. 406-410. PMID 18678527