Detection of Theileria orientalis genotypes and identification of potential vectors in Central Queensland

Abstract

<p>Theileria orientalis is a tick-borne protozoan parasite of bovine red blood cells inducing persistent infection. Clinical theileriosis, caused by T. orientalis has become a cattle disease of economic importance in Australia since 2006 with the emergence of pathogenic genotypes of the parasite. There is a scarcity of information on the identification of these genotypes and their epidemiology in central Queensland. We used recently developed molecular methods to differentiate and quantify pathogenic and non-pathogenic T. orientalis genotypes in cattle and ticks on a property near Capella, Central Queensland where clinical theileriosis is believed to be absent. Thirty blood samples were collected from cattle and ticks were collected off pasture and off animals fortnightly between February and June 2018. Real-time quantitative PCR (qPCR) analysis of the blood samples revealed a generic T. orientalis prevalence of 100% with prevalence of the different genotypes being 100% for Buffeli (non-pathogenic), 80% for Chitose (possibly pathogenic) and 0% for the pathogenic Ikeda genotype. Absolute quantification revealed similar parasite burdens of Buffeli and Chitose with no association between the two. It also revealed significantly higher Theileria burdens in sampled cows than heifers. On pasture, two tick types were detected, Amblyomma sp. (95.8%) and Haemaphysalis bancrofti (4.2%). The ticks collected from cattle were very different being 98.6% Rhipicephalus microplus and 1.4% Amblyomma triguttatum. Quantitative PCR of pooled tick head parts of the three tick species revealed high levels of genotype Buffeli in H. bancrofti and moderate levels in R. microplus. No other Theileria genotypes were detected. Based on these and other findings the most likely vector of T. orientalis in this area is Haemaphysalis bancrofti despite the lack of detection on cattle. Further research is required on the role of Rhipicephalus microplus. T. orientalis was endemic on this property but the most pathogenic genotype, Ikeda was absent.</p>