A Comparison of Bovine Torovirus Strains Based on Partial Membrane Glycoprotein (M) Gene Sequences

Bovine torovirus (BoTV), which was recently been separated from bovine coronaviruses, is one of the important causative agents of diarrhea in newborn calves. Although the epidemiological data are limited throughout the world, it has been reported in some countries of the world since the early 80’s. In this study, stool samples (n: 150) were taken from 0-30 days old diarrhoeic calves from Elazig, Sivas, and Malatya provinces and were screened by nested RT-PCR method. In 6% (9/150) of the studied samples, 409 bp partial membrane glycoprotein (M) gene was successfully amplified. Some of the positive samples were further sequenced and the 383 nt length data of nine samples were subjected to bioinformatic analysis. The multiple sequence comparison and phylogenetic analyses together revealed that these novel strains presented close identity to previously reported strains from Turkey. The nucleotide identity of the strains was found between 97.13% and 100%. Furthermore, valine-isoleucine substitution (V→I) at 114th position was detected in Turkish strains only (MN717266; MF687255-60), whereas the same substitution at the 144th position was shared between the Turkish (KF188708-11 and KF188714; MF687255-60; MG957145 and MN717266-67) and some of the Chinese-originated isolates. Moreover, four silent mutations were detected in the novel isolates subjected in this study. As a result, we demonstrated the contribution of BToV in the pathogenesis of calf diarrhea and presented new data concerning on the molecular characteristics and the epidemiology of the bovine toroviruses in Turkey.