First report of highly pathogenic Theileria luwenshuni in Sri Lanka: Are Jaffna sheep resistant to theileriosis?

Theileriosis is a tick-borne piroplasmid infection that affects small ruminant production, resulting in significant economic losses. This study investigated theileriosis and its potential vectors in the Jaffna sheep breed in Sri Lanka. Blood (n = 100) and ticks (n = 57) were randomly collected from three farms. Management practices and other demographic data were collected using a questionnaire. Giemsa-stained blood smears facilitated microscopic analysis of piroplasms. The prevalence of theileriosis was compared between farms, age, and gender categories using a Chi-square test or a Fisher's exact test. The molecular identification was achieved using a nested PCR targeting the 18S rRNA gene of Theileria spp. Subsequently, PCR amplicons were subjected to bidirectional sequencing and phylogenetic analysis. Microscopic examination and nested PCR revealed 38.0 % and 90.9 % prevalence of Theileria species, respectively, with a significant difference (p = 0.0015). The phylogenetic analysis showed that the Theileria spp. identified is the highly virulent Theileria luwenshuni. Collected tick species were: Haemaphysalis bipsinosa, Haemaphysalis intermedia, Rhipicephalus haemaphysaloides, Rhipicephalus linneai and Hyalomma marginatum isaaci; the most prevalent being H. bispinosa (68.4 %). This is the first report and molecular characterisation of T. luwenshuni in Sri Lanka, a highly pathogenic species recorded in small ruminants in tropical and subtropical countries but does not cause clinical signs in the Jaffna sheep breed. Findings of the current study suggest that Jaffna sheep tolerate the infection by T. luwenshuni. However, them being carriers poses a major risk to immunocompromised farm animals, especially the exotic sheep and goat breeds in the country.