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Pathogen Page

Theileria annulata

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Theileriosis

3. Introduction

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 vector ticks are of the genus Hyalomma. The most prominent symptoms are fever and lymph node enlargement. But there is a wide range of clinical manifestations, especially in enzootic areas. Among them, the Doukkala area of Morocco, where the epidemiology and symptomatology of the disease were minutely studied (Wiki: T. annulata).

4. Microbial Pathogenesis

Three stages in the life cycle of the parasite--tick-derived sporozoites, intramononuclear schizonts, and erythrocytic merozoites--infect cattle. When cattle are inoculated with schizont-infected cells, the parasite is transferred from the donor cell to the recipient. The main pathological damage in cattle is induced by the schizont stage. Each development stage of T. annulata elicits a specific immune response. Schizont-infected lymphoid cells can be grown indefinitely in culture and prolonged cultivation results in loss of virulence. Blood-derived schizonts induce stronger immunity than culture-derived schizonts, which suggests that restrictions on the parasite population or antigenic variation occur during prolonged cultivation. The duration of immunity following sporozoite or schizont infections has not yet been determined, but does not appear to be lifelong (Pipano and Shkap, 2000).

5. Host Ranges and Animal Models

Tropical theileriosis is maintained in nature by a cattle-tick-cattle cycle, both taurine (Bos taurus) and zebu (Bos indicus) cattle being susceptible to the disease. The yak (Bos grunniens) is also highly susceptible and suffers severe clinical symptoms and mortality following infection with T. annulata. The water buffalo (Bubalus bubalis) does not usually exhibit clinical manifestation on infection, but may act as a reservoir for the infection of ticks (Pipano and Shkap, 2000).

6. Host Protective Immunity

Each of the three developmental stages of T. annulata that are infective for cattle (sporozoites, schizonts, and erythrocytic merozoites) induces a specific immune response that may result in partial or no protection against infection with the heterologous stages (Pipano and Shkap, 2000).

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