First detection and phylogenetic analysis of porcine parainfluenza virus 1 and swine orthopneumovirus in swine reared on commercial farms in Serbia

Introduction Porcine parainfluenza virus 1 (PPIV1) and swine orthopneumovirus (SOV) are recently discovered respiratory viruses of swine. Data on their geographic distribution and genetic diversity are scarce. This study investigated the presence of these viruses in diseased pigs on commercial farms in Serbia and also the phylogenetic characteristics of the detected strains. Material and Methods A total of 131 samples were collected during passive surveillance of swine influenza in pigs from 10 commercial farms. All samples were screened by real-time RT-PCR for swine influenza A virus (SIV) and PPIV1, and 77 of them were tested for SOV. Positive samples were further subjected to conventional RT-PCR targeting the PPIV1 F and SOV G genes, sequencing, and phylogenetic analysis. Results Farm-level prevalence was 60% for SIV, 50% for PPIV1 and 10% for SOV. Overall, 27 samples were positive for SIV, 18 for PPIV1 and 2 for SOV. Co-circulation of two viruses was evident on four farms, and on one farm, all the tested viruses were detected. Phylogenetically, three Serbian PPIV1 strains clustered together with European and Asian strains, and SOV strains grouped with swine, murine and canine pneumoviruses, confirming their close evolutionary relationship. Conclusion This is the first evidence of PPIV1 and SOV circulation on pig farms in Serbia. Even established phylogenetic patterns are consistent with those reported in Europe, expanded surveillance is needed to better define the prevalence and genetic diversity of these emerging respiratory viruses in Serbian pig populations.