Can porcine astrovirus 4 (PoAstV4) alone cause respiratory disease? A new study is the first to confirm that PoAstV4 can be a primary cause of epitheliotropic viral infection in the respiratory tract of piglets.
A team of investigators from North Carolina State University, USDA Agricultural Research Service, Iowa State University, and University of California Santa Cruz set out to discover if piglets infected with PoAstV4 exhibited reproducible lesions in the respiratory tract. The study, funded by the Swine Health Information Center, was designed to infect PoAstV4 naïve piglets with the virus and characterizing the resulting infection and pathological lesions.
“PoAstV4 has frequently been detected in nasal swabs from young pigs exhibiting respiratory disease,” SHIC explains. “However, observational associations do not establish causation.”
Past studies, including an evaluation of 117 IAV negative cases of tracheitis and bronchitis, demonstrated a strong association between PoAstV4 detection in respiratory epitheliotropic viral infection lesions. SHIC says understanding the pathogenesis of PoAstV4 as an emerging virus is crucial for accurate diagnosis, differential considerations and effective management strategies for respiratory disease in swine.
How Did the Study Work?
The study evaluated caesarean-derived colostrum-deprived (CDCD) piglets challenged intratracheally with PoAstV4 PCR positive tissue homogenate that had been screened by next-generation sequencing for the presence of other primary swine pathogens. Nasal swabs were collected to monitor viral shedding, and piglets were necropsied at five- and eight-days post-challenge (DPC) to evaluate gross and microscopic lesions.
Viral localization within tissues was confirmed using PoAstV4 in situ hybridization, SHIC says. The immune response was characterized by detecting anti-PoAstV4 IgM and IgG antibodies in serum and quantifying infiltrating lymphocytes (T and B cells) within lesioned airways using immunohistochemistry and digital image analysis software.
Research Confirms Connection
“PoAstV4 was detected in nasal secretions of challenged piglets as early as two DPC,” SHIC reports. “All challenged piglets were negative for nasal shedding by 14 DPC, with peak shedding occurring earlier in the post-challenge period. Fecal shedding was also observed, suggesting either swallowed respiratory exudates or potential low-level gastrointestinal involvement.”
Researchers said microscopic lesions consistent with epitheliotropic viral infection, specifically tracheitis and bronchitis, were consistently observed in challenged pigs at five and eight DPC. PoAstV4 was successfully localized to the respiratory epithelial cells within these lesioned tissues via ISH, directly linking the virus to the observed pathology.
“A robust immune response was mounted against PoAstV4,” SHIC notes. “Both anti-PoAstV4 IgM and IgG antibodies were detected in serum, with IgG levels becoming detectable at 14 DPC and increasing through the study’s end at 21 DPC.”
In addition, significant infiltration of lymphocytes was observed within the lesioned respiratory mucosa of challenged pigs, indicating a cell-mediated immune response.
“The demonstration of both antibody and cell-mediated immune responses to PoAstV4 is foundational for understanding immunity and potential vaccine development strategies,” SHIC adds. “This study provides compelling evidence that PoAstV4 is a primary respiratory pathogen capable of causing tracheitis and bronchitis in young, naïve pigs.”
What’s Next?
Although the reproduced lesions in this controlled setting were not as severe or extensive as some field cases, SHIC notes this is likely influenced by the precise challenge dose and the optimal health conditions of CDCD piglets.
Results suggest that PoAstV4 should be considered a differential diagnosis for respiratory signs, particularly coughing, in suckling and early nursery pigs, especially in cases where common viral pathogens like IAV are not detected, SHIC adds.
:Future research efforts are critical to isolate PoAstV4 from clinical cases, which will enable more precise challenge studies, evaluation of the virus’s impact on production parameters, and assessment of its role in co-infections with other swine respiratory pathogens,” SHIC says.
