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{{short description|Subclass of parasitic eukaryotes}}
'''Hematozoa''' is a subclass of [[blood]] [[Parasitism|parasites]] of the [[Apicomplexa]] clade. Well known examples include the ''[[Plasmodium]]'' spp. which cause [[malaria]] in humans and ''[[Theileria]]'' which causes theileriosis in cattle. A large number of species are known to infect [[bird]]s and are transmitted by [[arthropod|insect]] [[Vector (epidemiology)|vectors]].<ref>{{Cite web|last=Slapeta|first=Jan|date=1982|title=Hematozoa|url=http://tolweb.org/Hematozoa_-_Aconoidasida/68058|access-date=9 April 2021|website=Tree of Life}}</ref> The pattern in which Haematozoa infect a host cell depends on the genera of the blood parasite. ''Plasmodium'' and ''Leucozytozoon'' displace the nucleus of the host cell so that the parasite can take control of the cell where as ''Hemoproteus'' completely envelops the nucleus in a host cell.<ref name=":1">{{Cite journal|last=Redig|first=Patrick, T.|date=2018|title=Haematozoa|journal=Encyclopedia of Reproduction|volume=6|issue=Second Edition|pages=631–636}}</ref>

Infections of haematozoa can have adverse fitness effects on certain species. Species that have been isolated or have not been exposed to the infection have been found to be especially vulnerable to [[pathogenic]] effects. The infection effects can persist in avian host species through long-distance [[Migration (ecology)|migrations]].

Blood parasites that have been studied were found to be transmitted by [[hematophagous]] (bloodsucking) [[dipteran]] (insect) vectors that have life stages in both aquatic and aerial environments.<ref>{{cite journal|last1=Smith|first1=Matthew M.|last2=Ramey|first2=Andrew M.|year=2015|title=Prevalence and genetic diversity of haematozoa in South American waterfowl and evidence for intercontinental redistribution of parasites by migratory birds|journal=International Journal for Parasitology: Parasites and Wildlife|volume=4|issue=1|pages=22–8|doi=10.1016/j.ijppaw.2014.12.007|pmc=4356868|pmid=25830104}}</ref>

== Plasmodium ==
[[File:Plasmodium_in_erythrocytic_cycle.jpg|alt=Microscopic view of Plasmodium in Erythrocytes|thumb|''Plasmodium'' in erythrocytic cycle]]
''[[Plasmodium]]'', a genus consisting of over 170 species, infects mammals, reptiles, birds, and amphibians. Blood parasites of the ''Plasmodium'' genus cause [[malaria]], which most commonly infect vertebrates with only four strains known to infect humans.<ref name=":1" /> Species of blood parasites that infect humans include ''Plasmodium falciparum, Plasmodium vivax, Plasmodiun ovale,'' and ''Plasmodium malariae''. The parasites are transmitted through malaria infected mosquitos which inject [[Apicomplexan life cycle|sporozoites]], the parasite's infective cells, into human hosts. When injected, sporozoites migrate to the liver where they replicate and rupture to increase the spread of the parasitic infection inside the host.<ref name=":1" /> The study of ''Plasmodium'' parasites has been significant in serving the role as a model organism for human malaria research. Similarities in pathological effects of parasites on avian hosts have been found in parasites infected with malaria in humans by transmission of [[mosquito]] bites.<ref name=":1" />

== Theileria ==
''[[Theileria]]'' is a haematozoan parasite, mainly found in coastal areas, that is transmitted by ''Haemaphysalis longicornis'' ticks that emerged from the Eastern hemisphere.<ref name=":0">{{cite journal|last1=Oakes|first1=Vanessa, J.|date=September 2019|title=Theileria orientalis Ikeda Genotype in Cattle, Virginia, USA|journal=Emerging Infectious Diseases|volume=25 |issue=9 |pages=1653–1659 |doi=10.3201/eid2509.190088|pmid=31237835 |pmc=6711211 |doi-access=free}}</ref> Cases of ''Theileria orientalis'' were recently found in the Eastern United States in 2017 where cattle in Virginia presented symptoms concurrent with the parasite. However, further investigation identified the tick to be prevalent in the United States as early as 2010, with eight other states along the coast detecting this parasite. The ''Theileria orientalis'' parasite, like other haematozoa, infect erythrocytes, causing chronic anemia resulting in illness and death of cattle. Infections by the tick parasite induce symptoms such as anemia, jaundice, and anorexia in cattle.<ref>{{cite journal|last1=Park|first1=Jingo|date=November 2016|title=Genetic characterization of Theileria orientalis from cattle in the Republic of Korea|url=https://link.springer.com/article/10.1007/s00436-016-5316-7|journal=Parasitology Research|volume=116 |issue=Springer Link|pages=449–454 |doi=10.1007/s00436-016-5316-7 |pmid=27817011 |s2cid=253985053 |url-access=subscription}}</ref> Cattle imported from prevalent ''Theileria orientalis'' areas are often quarantined from a naïve herd to prevent the spread of the parasite to susceptible cattle. Identification of ''Theileria orientalis'' is achieved by the sequencing of blood samples to identify two key features of the parasite, a small ribosomal subunit and a major piroplasm surface protein.<ref name=":0" />

== Avian infections ==
Avian haemosporidians include the ''Plasmodium'', ''[[Haemoproteus]]'', and ''[[Leucocytozoon]]'' genera. Avian species can have mixed infections in which multiple genera of haemosporidians are involved, which provides additional challenges in identification of the haemosporidian. Avian haemosporidians are expressed globally with the exception of polar regions. They are mainly found in wet tropical climates, which provide easy transmission of haematozoan infections. Avian species serve adequate hosts that transmit haematozoa during migratory periods, which increases fitness of the parasite.<ref>{{Cite journal|last1=Smith|first1=Matthew, M.|last2=Ramey|first2=Andrew, M.|date=2015-04-01|title=Prevalence and genetic diversity of haematozoa in South American waterfowl and evidence for intercontinental redistribution of parasites by migratory birds|journal=International Journal for Parasitology: Parasites and Wildlife|language=en|volume=4|issue=1|pages=22–28|doi=10.1016/j.ijppaw.2014.12.007|pmid=25830104 |pmc=4356868 |issn=2213-2244|doi-access=free}}</ref> Avian species that exist in large flocks, such as [[Anseriformes|Waterfowl]], are adequate hosts and easily transmit the infection due to close proximity in flocks. Symptoms of avian haemosporidians include anemia, weight loss, and mortality.<ref name=":3">{{Cite journal|last1=Ciloglu|first1=Arif|last2=Ellis|first2=Vincenzo A.|last3=Bernotienė|first3=Rasa|last4=Valkiūnas|first4=Gediminas|last5=Bensch|first5=Staffan|date=2019-01-01|title=A new one-step multiplex PCR assay for simultaneous detection and identification of avian haemosporidian parasites|url=https://doi.org/10.1007/s00436-018-6153-7|journal=Parasitology Research|language=en|volume=118|issue=1|pages=191–201|doi=10.1007/s00436-018-6153-7|pmid=30536121 |s2cid=253969176 |issn=1432-1955|url-access=subscription}}</ref> Haemosporidian parasites are detected by highly sensitive and specific [[Polymerase chain reaction|PCR]] techniques as well as microscopic examination.<ref name=":3" /> The parasites are important to understand the infections and strategies to prevent further transmission of the parasite.

== See also ==

* [[Plasmodium]]
* [[Theileria]]

==References==
{{Reflist}}

[[Category:Eukaryotic microbiology]]

Haematozoa - Revision history

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