Detection, isolation, and co-infection of parainfluenza virus 5 and porcine teschovirus 4 in colostrum-deprived piglets in Russia.

In recent years, parainfluenza virus 5 (PIV5) and porcine teschoviruses (PTVs) have been commonly identified during respiratory and enteric pathologies in industrial pig farming. While these viruses are widespread in pig populations of many countries, little is known about their circulation within Russian pig herds. In this study, we report the first evidence of PIV5 and PTV-4 in pigs in Russia, along with the occurrence of their co-infections. In total, 16 respiratory/oral samples obtained from colostrum-deprived piglets in 2021 on a pig farm located in Eastern Siberia were screened by qRT-PCR. Serum samples (n = 51) obtained in 2022 from this pig farm were tested using the virus neutralization assay. The PIV5 genome was identified in 75.0% of the samples, while PTV was detected in 31.3% exclusively as a co-infection with PIV5. Joint cultivation of two pathogens in a swine testis cell culture indicated that PIV5 became undetectable by the 6th passage, while the PTV Cq value remained stable from the 3rd up to the 10th passage. Phylogenetic analysis showed that the isolated strain belonged to PTV-4, and the PIV5 strain clustered exclusively with the Russian strain "Moskva," forming a divergent clade. The overall PTV-4 seroprevalence rate in tested pigs was estimated to be 70.6%. Our findings emphasize the necessity of monitoring PIV5 and PTV-4 as single and mixed infections in local pig herds to prevent diagnostic oversight and enhance infection control strategies in the future.