A Comparative Study of Single Theileria Lestoquardi and Mixed Infections with Theileria Ovis

Abstract

Background: Epidemiological surveys in Oman have revealed a high prevalence of the co-occurrence of the pathogenic T. lestoquardi and the non-pathogenic T. ovis among sheep in the Barka region, Oman. Our most recent data illustrated an interaction and reduced mortality risk in animals co-infected with T. lestoquardi and T. ovis, suggesting that the latter confers protection against pathogenicity of T. lestoquardi. The present study extends the above findings and examines disease outcomes; clinical markers, hematological parameters and parasite density in mixed and single T. lestoquardi infections. Methods: A total of 390 blood samples were collected from 16 sheep pens located in Barka, Oman between July and November 2019. Theileria spp were detected and quantified using qPCR assay targeting 18S rRNA, and the extent of genetic diversity was estimated by a panel of T. lestoquardi specific micro- and mini-satellites. The association of some disease markers with the presence of Theileria spp. and genetic diversity was tested. Results: Theileria spp were detected in 75 (19.2%) sheep; of these 65 (86.7%) had mixed infections (T. lestoquardi plus T. ovis), 8 (10.6%) were infected with T. lestoquardi alone and 2 (2.7%) with only T. ovis. Exotic breeds had a higher risk for Theileria spp infection. The density of both parasites was higher in single infection against mixed infection, and there was a relatively lower density of T. lestoquardi in mixed infections. However, there was no difference in hematological indices between single T. lestoquardi and mixed infections. High genetic diversity was observed among T. lestoquardi in Barka, with no differences of T. lestoquardi in single and mixed infections. The extent of diversity seen in Barka was higher (He = 0.772) than that reported in Oman in 2019 (He = 0.582), with distinct T. lestoquardi genotypes. Conclusion: The substantial prevalence of T. lestoquardi as mixed vs single infection supports the hypothesis that T. ovis confers protection against lethal T. lestoquardi infection. However, there were no differences in disease correlations (clinical markers, hematology parameters and density of parasites) or the extent of diversity of T. lestoquardi between the two types of infection. The presence of distinct T. lestoquardi genotypes in Barka, compared to that reported earlier in Oman, highlights the need for further analysis of the parasite populations to inform on novel approaches for controlling malignant theileriosis.