Detection of Theileria in cattle ticks (Rhipicephalus microplus) (Canestrini, 1888) in upper-northeastern Thailand.

Theileria parasites were investigated from cattle ticks (Rhipicephalus microplus (Canestrini, 1888)) collected in 12 provinces in upper-northeastern Thailand based on the sequences of 18S rRNA and MPSP gene. Polymerase chain reactions (PCRs) and sequencing specific regions for the 18S rRNA gene revealed two species of Theileria pathogens; T. orientalis (n=42) and T. sinensis (n=31) with 94.50-100% identity. In the provinces of upper-northeastern Thailand, the nucleotide diversity of Theileria's 18S rRNA for T. sinensis and T. orientalis were 0% and 1.3%. respectively. The MPSP gene was used to categorize the T. orientalis genotypes. The sequences were compared with those available in the public database (GenBank) for species identification. Phylogenetic trees of Theileria were constructed from the MPSP gene sequences of our amplicons and those available in GenBank using maximum-likelihood and neighbor-joining analyses. The results revealed three identified genotypes: type 3, 5, and 7. Although the main carriers of T. orientalis are ticks in the genus Haemaphysalis, T. orientalis was the most frequently found in R. microplus in upper-northeastern Thailand. Theileria was frequent in Nong Khai, Mukdahan, and Loei, three Thai provinces that bordered the Lao PDR close to the Mekong River. Epidemiological surveys and control strategies in this region should be considered.