Theileriosis

Definition

A tick-borne disease of domestic and wild ungulates caused by intracellular apicomplexan protozoans of the genus Theileria, characterized by fever, lymphadenopathy, anemia, and often fatal outcomes in naive hosts. The parasites undergo complex life cycles involving both vertebrate hosts and ixodid tick vectors, with schizogony in lymphocytes and erythrocytes of mammals and sporogony in tick salivary glands and gut epithelium.

Etymology

New Latin, from Theileria (genus name honoring Arnold Theiler, South African veterinary researcher) + -osis (disease condition)

Example

East Coast fever, caused by Theileria parva and transmitted by the brown ear tick Rhipicephalus appendiculatus, is the most economically important theileriosis in sub-Saharan Africa, killing up to 1 million cattle annually; control relies heavily on acaricide treatment of tick vectors and infection-and-treatment immunization of cattle.

Synonyms

• theileriasis

Related Terms

• apicomplexa
• Ixodidae
• vector-borne disease
• Babesiosis
• East Coast fever
• tropical theileriosis
• acaricide
• tick-borne pathogen
• piroplasm

Usage Notes

Distinguished from babesiosis (caused by Babesia spp.) by the presence of schizont stages in lymphocytes; Theileria causes both lymphoid and erythrocytic infection, whereas Babesia is restricted to erythrocytes. The term is used primarily in veterinary contexts; human theileriosis (T. microti) is rare and often subclinical. Control strategies emphasize tick vector management rather than direct parasite treatment due to drug resistance and the intracellular nature of the pathogen.