Isolation and characterization of a swine parainfluenza virus 5 strain from Southwest China

Parainfluenza virus type 5 (PIV5) can infect a variety of animals and can lead mainly to respiratory symptoms. In recent years, PIV5 has been frequently detected in swine fecal samples with diarrhea symptoms, but its role in pig diseases remains unclear. In this study, a swine PIV5 strain, CHN-SCMY2025, was isolated from diarrheal piglets in Sichuan Province, Southwest China. The cytopathic effect of the isolate was systematically characterized by electron microscopy and immunofluorescence. The results demonstrated that CHN-SCMY2025 is approximately 150–250 nm in diameter and has a morphology typical of parainfluenza virus. In addition to Vero cells, CHN-SCMY2025 exhibits broad cellular tropism and can replicate in BHK-21, LLC-PK, IPEC-J2, ST, and 293 T cells. Sequence alignment based on the NP (PX583268.1), HN (PX583267.1), F (PX583266.1), M (PX963773.2), and L (PZ011079.1) of CHN-SCMY2025 was determined, which shares 95.83–99.82%, 96.53–99.88%, 96.67–100%, 95.51–99.21%, and 97.89–99.78% nucleotide identity with other PIV5 reference strains in GenBank, respectively. Phylogenetic analysis revealed that CHN-SCMY2025 is closely related to the swine PIV5 isolate (KC237064.1). In vivo infection demonstrated that CHN-SCMY2025 could induce mild to moderate respiratory symptoms and mild diarrhea in suckling piglets. The virus was shed daily in the feces of infected suckling piglets and upon necropsy. The virus was distributed in multiple organs, but relatively high viral loads were detected mainly in the lung, duodenum, and jejunum. CHN-SCMY2025 is the first systematically characterized swine PIV5 strain from southwestern China. Our results provide information on epidemiology, pathogenicity, and interspecies transmission associated with swine PIV5.