Comparative aspects of Theileria lestoquardi and Theileria annulata infections of sheep and cattleLeemans, Ingrid
Theileria annulata and T. lestoquardi are apicomplexan protozoan parasites of domestic livestock in northern Africa, Asia and southern Europe, transmitted by ticks ofthe genus Hyalomma. This thesis deals with comparative aspects of infections of the two parasite species in sheep and cattle.
To validate an indirect fluorescent antibody test for diagnosis of T. lestoquardi infection, the antibody response was monitored in sheep infected with T. lestoquardi schizont infected cells cultivated in vitro. Post-infection sera showed a high level of cross-reactivity to T. annulata schizont antigen.
In a series of experimental infections, based on the inoculation of sporozoites from ticks, the infectivity and the pathogenicity ofthe two parasite species for sheep and cattle were compared. T. lestoquardi caused serious disease in sheep but failed to infect cattle. In contrast, T. annulata infected both cattle and sheep. But while it caused severe disease in cattle, infections of sheep were mild and piroplasms did not develop. In vitro infection of ovine and bovine peripheral blood mononuclear cells with sporozoites ofthe two parasite species confirmed the findings in vivo. Since T. annulata did not complete its lifecycle in the sheep, infection of this host is unlikely to play a role in the epidemiology of T. annulata infection in cattle.
Cross-immunity studies in sheep showed that these animals were partially protected against challenge infection with the heterologous parasite species. This provided further indication of a close relationship between these two parasites.
Parasite infected cell lines from the above infections were analysed for their expression of cell surface antigens. The two parasite species appeared to have infected macrophages and B cells in both sheep and cattle. Differences in expression of leukocyte subpopulation antigens were quantitative rather than qualitative. Consequently, neither similarities nor differences in the course of clinical infection ofsheep with T. lestoquardi and ofsheep and cattle with T. annulata could be explained on the basis of phenotypic characterization only.
Keywordstick-borne disease; tropical bovine theileriosis; malignant ovine theileriosis; protozoa; sub-tropics; antigens; susceptibility; cross-protection; flow cytometry
Published inActa Universitatis Agriculturae Sueciae. Veterinaria
2001, number: 107
Publisher: Swedish University of Agricultural Sciences
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