Experimental Porcine Astrovirus 4-Associated Tracheitis and Bronchitis in Pigs.

Porcine astrovirus 4 (PoAstV4) is an emerging pathogen that has previously been associated with respiratory disease in piglets. The objective of this study was to inoculate naïve piglets with PoAstV4 and characterize the host-pathogen interaction and pathological lesions. Cesarean-derived colostrum-deprived (CDCD) piglets were inoculated intratracheally and intranasally with PoAstV4 PCR-positive tissue homogenate previously screened for the presence of other primary pathogens with next-generation sequencing (NGS). Nasal and fecal swabs for PCR identification of PoAstV4 were collected pre and postinoculation. Animals were euthanized at 5, 8, and 21 days postinoculation (DPI) and tissues were collected for histopathologic and digital image analysis. Nasal swabs were PCR positive for PoAstV4 from 2 DPI to 10 DPI. Microscopic lesions of epitheliotropic viral infection of the trachea and bronchi, including epithelial attenuation and lymphoplasmacytic infiltration, were found in inoculated pigs at 5 DPI and 8 DPI. PoAstV4 was localized to the lesions demonstrated by in situ hybridization and quantified by digital image analysis. In addition, PoAstV4-inoculated pigs at 8 DPI had an abundance of infiltrating lymphocytes predominated by T cell lymphocytes characterized by immunohistochemistry (IHC) and quantified using digital image analysis. Both anti-PoAstV4 IgM and IgG were detected in serum, with IgG levels first detectable at 14 DPI and increasing to the end of the study at 21 DPI. The presented findings confirm the respiratory epithelial tropism of PoAstV4 while also characterizing viral shedding and host immune response dynamics.