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a genus of parasitic protozoans of the family Theileriidae that parasitize cells of the reticuloendothelial system and the erythrocytes in animals.

Several species have been described as causing the disease theileriasis: T. annulata, T. parva, T. mutans, T. dispar, and T. sergenti in cattle; T. ovis, T. hirci, and T. recondita in sheep and goats; T. tarandirangiferis in reindeer; and T. cervi in other deer. T. annulata, T. sergenti, and T. tarandirangiferis are responsible for much economic damage in the USSR. Ixodids have been shown to be vectors of Theileria; the vectors of Theileria in deer have not yet been identified.

Theileria can survive in warm-blooded animals for years; in ticks, they survive for a single generation. The protozoans enter the body of a warm-blooded host with the saliva of the tick vector when the tick feeds. After reaching the nearest lymph nodes, they penetrate the reticuloendothelial cells. There they multiply by schizogony and form macroschizonts and microschizonts (Koch’s blue bodies) up to 30 micrometers in diameter and sometimes larger. They then penetrate other lymph nodes, parenchymatous organs, and the peripheral blood. Schizonts are also found outside of cells in cases of mass infection. On disintegration, a schizont produces a larger number of parasites that penetrate the erythrocytes. A single erythrocyte may contain one to four or, sometimes, more parasites. The parasites may be round (0.5–2 micrometers in diameter) or elongated (up to 4–5 micrometers long); other shapes have also been observed. The cytoplasm and nucleus of the parasite can be readily discerned in stained blood smears. The parasites reproduce in erythrocytes by dividing into two or four individuals. Theileria present in the blood of animals are the source of infection of ticks.


References in periodicals archive ?
Prevalence of Theileria annulata infection in Indian water buffaloes in and around Bareilly, U.
26) Theileria ovis (GenBank accession JQ737135) was designated as the outgroup.
KC465972; 91% identity) and Theileria orientalis (GenBank accession no.
Abnormality of osmotic fragility and morphological disorder of bovine erythrocytes infected with Theileria sargonti.
Rhipicephalus appendiculatus is responsible for the transmission of corridor disease via the cattle-buffalo association (since 1989, the different forms of the parasite are referred to as Theileria parva buffalo-associated--buffalo to cattle transmission; and Th.
Researchers are in their fifth year of a collaborative project, "Combination Vaccines for Tick-Borne Diseases," which involves studying the tick, Rhipicephalus appendiculatus, that transmits Theileria parva, the parasite responsible for ECF.
In a visit to the cattle Camp in Bor, a cattle keeper, Gai Deng told Sudan Tribune that their camp is affected by East Coast Fever, a tick- borne protozoan infection caused by Theileria parva that killed over 10,000 cattle since it started three years ago.
Theileria annulata is one of the most famous species of theileria genus and is transmitted by Hyalomma spp.
Induction of Theileria sergenti infection in splenectomized calf by Haemaphysalis longicornis.
Single dilution ELISAs using soluble piroplasm, cellular schizont and soluble schizont antigens for the detection of antibodies against Theileria annulata.
MPSS(TM) will be applied initially to study the life cycle of Theileria parva, an intracellular protozoan parasite responsible for east coast fever, a serious tick-borne cattle disease that transforms bovine lymphocytes to a leukemia-like state.
A total of five microfilariae and one theileria were recorded.