Plasmodium
Plasmodium | |
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False-colored sporozoite
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Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Alveolata |
Phylum: | Apicomplexa |
Class: | Aconoidasida |
Order: | Haemospororida |
Family: | Plasmodiidae |
Genus: | Plasmodium Marchiafava & Celli, 1885 |
Plasmodium is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of Plasmodium species involve development in a blood-feeding insect host which then injects parasites into a vertebrate host during a blood meal. Parasites grow within a vertebrate body tissue (often the liver) before entering the bloodstream to infect red blood cells. The ensuing destruction of host red blood cells can result in malaria. During this infection, some parasites are picked up by a blood-feeding insect (mosquitoes in majority cases), continuing the life cycle.[1]
Plasmodium is a member of the phylum Apicomplexa, a large group of parasitic eukaryotes. Within Apicomplexa, Plasmodium is in the order Haemosporida and family Plasmodiidae. Over 200 species of Plasmodium have been described, many of which have been subdivided into 14 subgenera based on parasite morphology and host range. Evolutionary relationships among different Plasmodium species do not always follow taxonomic boundaries; some species that are morphologically similar or infect the same host turn out to be distantly related.
Species of Plasmodium are distributed globally wherever suitable hosts are found. Insect hosts are most frequently
Although the parasite can also infect people via blood transfusion, this is very rare, and Plasmodium cannot be spread from person to person. Some of subspecies of Plasmodium are obligate intracellular parasites.
Description
The genus Plasmodium consists of all
Like other apicomplexans, Plasmodium species have several cellular structures at the
Species of Plasmodium also contain two large membrane-bound organelles of
Life cycle
The life cycle of Plasmodium involves several distinct stages in the insect and vertebrate hosts. Parasites are generally introduced into a vertebrate host by the bite of an insect host (generally a mosquito, with the exception of some Plasmodium species of reptiles).[10] Parasites first infect the liver or other tissue, where they undergo a single large round of replication before exiting the host cell to infect erythrocytes.[11] At this point, some species of Plasmodium of primates can form a long-lived dormant stage called a hypnozoite.[12] It can remain in the liver for more than a year.[13] However, for most Plasmodium species, the parasites in infected liver cells are only what are called merozoites. After emerging from the liver, they enter red blood cells, as explained above. They then go through continuous cycles of erythrocyte infection, while a small percentage of parasites differentiate into a sexual stage called a gametocyte which is picked up by an insect host taking a blood meal. In some hosts, invasion of erythrocytes by Plasmodium species can result in disease, called malaria. This can sometimes be severe, rapidly followed by death of the host (e.g. P. falciparum in humans). In other hosts, Plasmodium infection can apparently be asymptomatic.[10]
Even when humans have such subclinical plasmodial infections, there can nevertheless be very large numbers of multiplying parasites concealed in, particularly, the spleen and bone marrow. Certainly, this applies in the case of P. vivax. These hidden parasites (in addition to hypnozoites) are thought to be the origin of instances of recurrent P. vivax malaria.[14]
Within the red blood cells, the merozoites grow first to a ring-shaped form and then to a larger form called a
In the mosquito, the gametocytes move along with the
Evolution and taxonomy
Taxonomy
Plasmodium belongs to the
The genus Plasmodium consists of over 200 species, generally described on the basis of their appearance in blood smears of infected vertebrates.[18] These species have been categorized on the basis of their morphology and host range into 14 subgenera:[17]
- Subgenus Asiamoeba (Telford, 1988) – reptiles
- Subgenus Bennettinia(Valkiunas, 1997) – birds
- Subgenus Carinamoeba (Garnham, 1966) – reptiles
- Subgenus Giovannolaia (Corradetti, et al. 1963) – birds
- Subgenus Haemamoeba (Corradetti, et al. 1963) – birds
- Subgenus Huffia (Corradetti, et al. 1963) – birds
- Subgenus Lacertamoeba (Telford, 1988) – reptiles
- Subgenus Laverania (Bray, 1958) – great apes, humans
- Subgenus Novyella (Corradetti, et al. 1963) – birds
- Subgenus Ophidiella (Telford, 1988) – reptiles
- Subgenus Paraplasmodium (Telford, 1988) – reptiles
- Subgenus Plasmodium (Bray, 1955) – monkeys and apes
- Subgenus Sauramoeba (Garnham, 1966) – reptiles
- Subgenus Vinckeia (Garnham, 1964) – mammals inc. primates
Species infecting
Phylogeny
More recent studies of Plasmodium species using molecular methods have implied that the group's evolution has not perfectly followed taxonomy.[2] Many Plasmodium species that are morphologically similar or infect the same hosts turn out to be only distantly related.[21] In the 1990s, several studies sought to evaluate evolutionary relationships of Plasmodium species by comparing ribosomal RNA and a surface protein gene from various species, finding the human parasite P. falciparum to be more closely related to avian parasites than to other parasites of primates.[17] However, later studies sampling more Plasmodium species found the parasites of mammals to form a clade along with the genus Hepatocystis, while the parasites of birds or lizards appear to form a separate clade with evolutionary relationships not following the subgenera:[17][22]
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Estimates for when different Plasmodium lineages diverged have differed broadly. Estimates for the diversification of the order Haemosporida range from around 16.2 million to 100 million years ago.[17] There has been particular interest in dating the divergence of the human parasite P. falciparum from other Plasmodium lineages due to its medical importance. For this, estimated dates range from 110,000 to 2.5 million years ago.[17]
Distribution
Plasmodium species are distributed globally. All Plasmodium species are parasitic and must pass between a vertebrate host and an insect host to complete their life cycles. Different species of Plasmodium display different host ranges, with some species restricted to a single vertebrate and insect host, while other species can infect several species of vertebrates and/or insects.
Vertebrates
Plasmodium parasites have been described in a broad array of vertebrate hosts including reptiles, birds, and mammals.[23] While many species can infect more than one vertebrate host, they are generally specific to one of these classes (such as birds).[23]
Humans are primarily infected by
Over 150 species of Plasmodium infect a broad variety of birds. In general each species of Plasmodium infects one to a few species of birds.[28] Plasmodium parasites that infect birds tend to persist in a given host for years or for the life time of the host, although in some cases Plasmodium infections can result in severe illness and rapid death.[29][30] Unlike with Plasmodium species infecting mammals, those infecting birds are distributed across the globe.[28]
A number of
Insects
In addition to a vertebrate host, all Plasmodium species also infect a bloodsucking insect host, generally a mosquito (although some reptile-infecting parasites are transmitted by sandflies). Mosquitoes of the genera Culex, Anopheles, Culiseta, Mansonia and Aedes act as insect hosts for various Plasmodium species. The best studied of these are the Anopheles mosquitoes which host the Plasmodium parasites of human malaria, as well as Culex mosquitoes which host the Plasmodium species that cause malaria in birds. Only female mosquitoes are infected with Plasmodium, since only they feed on the blood of vertebrate hosts.[36] Different species affect their insect hosts differently. Sometimes, insects infected with Plasmodium have reduced lifespan and reduced ability to produce offspring.[37] Further, some species of Plasmodium appear to cause insects to prefer to bite infected vertebrate hosts over non-infected hosts.[37][38][39]
History
In 1966, Cyril Garnham proposed separating Plasmodium into nine subgenera based on host specificity and parasite morphology.[18] This included four subgenera that had previously been proposed for bird-infecting Plasmodium species by A. Corradetti in 1963.[42][19] This scheme was expanded upon by Sam R. Telford in 1988 when he reclassified Plasmodium parasites that infect reptiles, adding five subgenera.[20][18] In 1997, G. Valkiunas reclassified the bird-infecting Plasmodium species adding a fifth subgenus: Bennettinia.[19][43]
See also
Notes
References
- ^ "CDC – Malaria Parasites – About". CDC: Malaria. U.S. Centers for Disease Control and Prevention. Retrieved 28 December 2015.
- ^ a b Zilversmit, M.; Perkins, S. "Plasmodium". Tree of Life Web Project. Retrieved 1 June 2016.
- PMID 27475118.
- ^ PMID 26844642.
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- ^ PMID 23186105.
- ^ PMID 23927894.
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- ^ ISBN 978-3-540-29088-9.
- ^ a b c "CDC – Malaria Parasites – Biology". CDC: Malaria. U.S. Centers for Disease Control and Prevention. Retrieved 28 December 2015.
- S2CID 1727294.
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- ^ Votypka J. "Haemospororida Danielewski 1885". Tree of Life. Retrieved 1 May 2018.
- ^ S2CID 21291855.
- ^ ISBN 978-1908230072.
- ^ ISBN 9780415300971.
- ^ a b Telford S (1988). "A contribution to the systematics of the reptilian malaria parasites, family Plasmodiidae (Apicomplexa: Haemosporina)". Bulletin of the Florida State Museum Biological Sciences. 34 (2): 65–96.
- PMID 14711087.
- PMID 18248741.
- ^ ISBN 978-2-7420-0616-8. Retrieved 15 March 2018.
- PMID 27777030.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ^ PMID 29096194.
- ISBN 978-0198565840. Retrieved 16 March 2018.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - S2CID 22397021.
- ^ ISBN 9780415300971.
- ISBN 9780415300971.
- ISBN 9780415300971.
- ^ ISBN 978-0127826202. Retrieved 16 March 2018.
- ^ PMID 28777791.
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- ^ PMID 28942108.
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- ^ a b c d e f "The History of Malaria, an Ancient Disease". U.S. Centers for Disease Control and Prevention. Retrieved 31 May 2016.
- ^ PMID 22738856.
- ^ Corradetti A.; Garnham P.C.C.; Laird M. (1963). "New classification of the avian malaria parasites". Parassitologia. 5: 1–4.
- ISSN 1392-1657.
Further reading
Identification
- Garnham, P. C. (1966). Malaria Parasites And Other Haemosporidia. Oxford: Blackwell. ISBN 978-0397601325.
- Valkiunas, Gediminas (2005). Avian Malaria Parasites and Other Haemosporidia. Boca Raton: CRC Press. ISBN 9780415300971.
Biology
- Baldacci, P.; Ménard, R. (October 2004). "The elusive malaria sporozoite in the mammalian host". Mol. Microbiol. 54 (2): 298–306. S2CID 30488807.
- Bledsoe, G. H. (December 2005). "Malaria primer for clinicians in the United States" (PDF). South. Med. J. 98 (12): 1197–204, quiz 1205, 1230. S2CID 30660702. Archived from the original(PDF) on 2009-03-26.
- Shortt, H. E. (1951). "Life-cycle of the mammalian malaria parasite". Br. Med. Bull. 8 (1): 7–9. PMID 14944807.
History
- Slater, L. B. (2005). "Malarial birds: modeling infectious human disease in animals". Bull Hist Med. 79 (2): 261–94. S2CID 23594155.