Development of a duplex PCR assay for detecting Theileria luwenshuni and Anaplasma phagocytophilum in sheep and goats

Coinfections with the tick-borne pathogens Theileria luwenshuni and Anaplasma phagocytophilum can cause significant economic losses in sheep and goat farming. The difficulty in detecting these two pathogens by microscopic examination warrants the development of a rapid detection test to discriminate them. In this study, a duplex polymerase chain reaction (PCR) assay was developed to simultaneously detect T. luwenshuni and A. phagocytophilum. Alignment of the sequences from related pathogens allowed us to design a primer pair targeting the 18S ribosomal RNA gene in T. luwenshuni and generate a target product of 962 bp, whereas a previously reported species-specific primer (SSAP2f/SSAP2r) for A. phagocytophilum was used in the same reaction to generate a product of 641 bp. Genomic DNA from T. luwenshuni and A. phagocytophilum was 10-fold serially diluted for testing PCR sensitivity. Under the optimal PCR conditions we established, the lower limit of detection of the assay was 29.13 fg/μL for T. luwenshuni and 1.53 fg/μL for A. phagocytophilum, and PCR primers used in this study were confirmed to be 100% species-specific using other hemoparasites previously identified by other methods. No significant difference was found between conventional and duplex PCR protocols used to detect the two species. Our study provides an effective, sensitive, specific, and accurate tool for the diagnosis and epidemiological surveillance of mixed infections of the two pathogens in sheep and goats.