Molecular epidemiology and phylogenetic analysis of Theileria species in sheep

A molecular epidemiological survey was carried out on theileriosis in sheep in six districts of northern Karnataka (India) from August 2017 to October 2018. A total of 525 (209 clinical cases and 316 healthy/tick infested) sheep blood samples were collected and analyzed by polymerase chain reaction (PCR) targeting 18S rRNA gene. In Theileria genus-specific PCR, 350 (148 clinical cases and 202 healthy/tick infested) samples showed specific amplification of 1098 bp DNA fragment with an overall prevalence of 66.67%. The prevalence of theileriosis among ages, genders and breeds in sheep was non-significant (P>0.05). In Theileria species-specific PCR, 297 (84.85%) samples amplified 389 bp fragment specific for T. luwenshuni and 6 (1.71%) samples amplified 520 bp fragment specific for T. ovis. T. luwenshuni was most predominant species followed by T. ovis with a mixed infection of 13.42%. In phylogenetic analysis by maximum likelihood, T. luwenshuni of north Karnataka isolate shared >99.5% homology with Indian isolates of T. luwenshuni and >99.2% homology with T. luwenshuni isolates of Chinese origin. T. ovis of north Karnataka isolate shared >99.8% homology with T. ovis isolates of Indian and Chinese origin. The findings indicated that PCR and phylogenetic analysis can be better molecular tools for understanding the molecular epidemiology and characterization of Theileria spp. at species level.