''Theileria'' is a genus of parasites that belongs to the phylum

Apicomplexa The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. Th ...

, and is closely related to ''

Plasmodium ''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 ver ...

''. Two ''Theileria'' species, ''T. annulata'' and ''T. parva'', are important cattle parasites. ''T. annulata'' causes tropical theileriosis and ''T. parva'' causes

East Coast fever East Coast fever, also known as theileriosis, is a disease of cattle which occurs in Africa and is caused by the protozoan parasite '' Theileria parva''. The primary vector which spreads ''T. parva'' between cattle is a tick, '' Rhipicephalus ap ...

. ''Theileria'' species are transmitted by ticks. The

genomes In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

of ''T. orientalis'' Shintoku'', Theileria equi'' WA, ''Theileria annulata'' Ankara and ''Theileria parva'' Muguga have been sequenced and published. ''Theileria equi'' is a known cause of equine piroplasmosis. Vaccines against ''Theileria'' are in development. In May 2010, a vaccine that was reported to protect cattle against East Coast fever had been approved and registered by the governments of Kenya, Malawi, and Tanzania.

Description

Species in this genus undergo exoerythrocytic

merogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...

in the

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...

histiocyte A histiocyte is a vertebrate cell that is part of the mononuclear phagocyte system (also known as the reticuloendothelial system or lymphoreticular system). The mononuclear phagocytic system is part of the organism's immune system. The histiocyt ...

erythroblast A nucleated red blood cell (NRBC), also known by several other names, is a red blood cell that contains a cell nucleus. Almost all vertebrate organisms have hemoglobin-containing cells in their blood, and with the exception of mammals, all of t ...

s, and other cells of the internal organs. This is followed by invasion of the erythrocytes by the

merozoite Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

s, which may or may not reproduce. When merogony does occur, no more than four daughter cells are produced. The frequent occurrence of elongated bacillary or "bayonet" forms within the erythrocyte is considered as characteristic of this genus. The organism is transmitted by various tick species, including ''

Rhipicephalus ''Rhipicephalus'' is a genus of ticks in the family Ixodidae, the hard ticks, consisting of about 74 or 75 species. Most are native to tropical Africa.Olwoch, J. M., et al. (2007)Climate change and the genus ''Rhipicephalus'' (Acari: Ixodidae) in ...

Dermacentor ''Dermacentor'' is a genus of ticks in the family Ixodidae, the hard ticks. The genus has a cosmopolitan distribution, with native species on all continents except Australia. Most occur in the Nearctic realm. Hosts of ''Dermacentor'' ticks incl ...

'', and''

Haemaphysalis ''Haemaphysalis'' is a genus of ticks, containing these species: *'' Haemaphysalis aborensis'' Warburton, 1913 *'' Haemaphysalis aciculifer'' Warburton, 1913 *'' Haemaphysalis aculeata'' Lavarra, 1904 *'' Haemaphysalis adleri'' Feldman-Muhsam, 1 ...

''. The organism reproduces in the tick as it progresses through its life stages.Theileria
reviewed and published by

WikiVet WikiVet is a wiki of veterinary content based on the MediaWiki platform. The website is a collaborative initiative between various veterinary schools, and its content covers the entire veterinary curriculum. WikiVet is part of the WikiVet Educatio ...

, accessed 11 October 2011. Both ''T. annulata'' and ''T. parva'' induce transformation of infected cells of

or macrophage/monocyte lineages. ''T. orientalis'' does not induce uncontrolled proliferation of infected leukocytes and instead multiplies predominantly within infected erythrocytes.

Genomics

The genomes of ''T. orientalis'' Shintoku'', Theileria equi'' WA, ''Theileria annulata'' Ankara and ''Theileria parva'' Muguga have been sequenced. Genomic data can be accesse
PiroplasmaDB
which is part of the Eukaryotic Pathogen Bioinformatic Resource ( EuPathDB).

Evolution

The genus is thought to have first appeared in

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

s during the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

. It is named for Gertrud Theiler, daughter of Arnold Theiler.

Transmission

''Theileria'' spp. can be transmitted to cattle through tick bites, including the brown ear tick, a ''

'' sp.

Important species

*''T. parva'' is the cause of bovine theileriosis and

. *''T. annulata'' also is a cause of bovine theileriosis. *''T. equi'' causes equine piroplasmosis. It was originally classified as ''Babesia equi'' in 1901 by Charles Louis Alphonse Laveran, but was reclassified as ''T. equi'' in 1998 by Heinz Mehlhorn and Eberhard Schein.

Treatment

* Buparvaquone is a promising compound for the therapy and prophylaxis of all forms of theileriosis.

References

External links

''Theileria annulata'' sequencing project''Theileria parva'' sequencing projectPiroplasmaDB
— genomic and functional genomic resource for piroplasmida {{Taxonbar, from=Q5233857 Piroplasmida Apicomplexa genera