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

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Apicomplexa The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an ap ...

, 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 Hematophagy, blood-feeding insect host (biology), host which then inj ...

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

tropical theileriosis Tropical theileriosis or Mediterranean theileriosis is a theileriosis of cattle from the Mediterranean and Middle East area, from Morocco to Western parts of India and China. It is a tick-borne disease, caused by ''Theileria annulata''. The vecto ...

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 (epidemiology), vector which spreads ''T. parva'' between cattle is a tic ...

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

genomes 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 genes, other functional regions of the genome such as ...

of ''T. orientalis'' Shintoku'', Theileria equi'' WA, ''Theileria annulata'' Ankara and ''Theileria parva'' Muguga have been sequenced and published. ''Theileria equi'' infects equid blood cells causing equine piroplasmosis. The disease presents with a variety of clinical conditions, such as fever, depression, jaundice, cramps, haemolytic anaemia, hemoglobinuria and even death, but asymptomatic infections are frequently observed. The most common vectors are the ticks ''Dermacentor nitens'' and ''Rhipicephalus microplus'' but ''Amblyomma cajennense'' was also implicated in the disease transmission. 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 ...

in the

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include T cells (for cell-mediated and cytotoxic adaptive immunity), B cells (for humoral, antibody-driven adaptive immunity), an ...

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 histiocy ...

erythroblast A nucleated red blood cell (NRBC), also known by #Nomenclature, 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 mamm ...

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 i ...

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,

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 are found in North America. Hosts of ''Dermacentor'' ticks inclu ...

'', 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

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

/monocyte lineages. ''T. orientalis'' does not induce uncontrolled proliferation of infected leukocytes and instead multiplies predominantly within infected erythrocytes. Following infection with ''Theileria equi'', horses may develop detectable antibodies, with seroprevalence varying widely across regions. Serological surveys have revealed a high prevalence of ''T. equi'' antibodies in horses and other equids, including 39.8% in Central-Southern Italy and 33.4% in Northern Brazil.

Genomics

The genomes of ''T. orientalis'' Shintoku'', Theileria equi'' WA, ''Theileria annulata'' Ankara and ''Theileria parva'' Muguga have been sequenced. Genomic data can be accessed thoug
PiroplasmaDB
which is part of the

Eukaryotic Pathogen Database The Eukaryotic Pathogen Vector and Host Database, or VEuPathDB, is a database of genomics and experimental data related to various eukaryotic pathogens. It was established in 2006 under a National Institutes of Health program to create Bioinforma ...

Evolution

The genus is thought to have first appeared in

ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...

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 parasitologist

Gertrud Theiler Gertrud Theiler (11 September 1897 – 2 May 1986) was a South African parasitologist and teacher most noted for her work with nematodes and ticks. Early life Born on 11 September 1897 in Pretoria, South Africa, Theiler graduated from Pretor ...

, daughter of

Arnold Theiler Sir Arnold Theiler KCMG (26 March 1867 – 24 July 1936) Pour le Mérite is considered to be the father of veterinary science in South Africa. He was born in Frick, Canton Aargau, Switzerland. He received his higher education, and later qu ...

Transmission

''Theileria'' spp. can be transmitted to cattle through tick bites, including the brown ear tick, a '' Rhipicephalus'' 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 Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a ''Babesia'' or ''Theileria'', in the phylum Apicomplexa. Human babesiosis transmission via t ...

. It was originally classified as ''Babesia equi'' in 1901 by

Charles Louis Alphonse Laveran Charles Louis Alphonse Laveran (18 June 1845 – 18 May 1922) was a French physician who won the Nobel Prize in Physiology or Medicine in 1907 for his discoveries of parasitic protozoans as causative agents of infectious diseases such as malaria ...

, but was reclassified as ''T. equi'' in 1998 by Heinz Mehlhorn and Eberhard Schein.

Treatment

Buparvaquone Buparvaquone is a naphthoquinone antiprotozoal drug related to atovaquone. It is a promising compound for the therapy and prophylaxis of all forms of theileriosis. Buparvaquone has been shown to have anti-leishmanial activity ''in vitro''. It c ...

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

References

External links

''Theileria annulata'' sequencing project''Theileria parva'' sequencing project
*
PiroplasmaDB
— genomic and functional genomic resource for

piroplasmida Piroplasmida is an order of parasites in the phylum Apicomplexa. They divide by binary fission and as sporozoan parasites they possess sexual and asexual phases (sexual reproduction occurs in the tick gut). They include the tick parasites ''Ba ...

{{Authority control Piroplasmida Apicomplexa genera