Respiratory disease is a major cause of morbidity, mortality and economic loss in swine production. Recent research has identified porcine astrovirus type 4 (PoAstV4) in pigs with respiratory disease and associated the virus with lesions including tracheitis, bronchitis and respiratory epithelial damage.
Despite its widespread prevalence and clear potential to exacerbate respiratory disease and coughing, no commercial vaccines are currently available.
The Missing Links
“Important questions remain about when pigs become infected with PoAstV4, how immunity changes throughout production, and when animals are most vulnerable,” says Seth Reicks, a veterinary student at the University of Minnesota College of Veterinary Medicine who investigated the virus during an internship with Pipestone Veterinary Services.
To fill these knowledge gaps, Reicks conducted a cross-sectional study on a commercial breed-to-finish system (negative for PRRSV wild-type, Mycoplasma hyopneumoniae and influenza). Blood and nasal swabs were collected from 390 pigs across 13 distinct production stages (30 pigs per group):
- Replacement Gilts (GDU): Nursery (6–8 weeks of age [WOA]), grower (9–12 WOA), early-finisher (14–15 WOA), late-finisher (20–22 WOA), heat-no-serve (24–28 WOA), and mid-gestation (88 WOA).
- Breeding Dams: Mid-gestation, farrowing, and weaning/service, split evenly between parity-one (P1) and parity-two (P2) sows.
- Downstream Pigs: Newborn (0 WOA), wean-age (3 WOA), nursery (6 WOA), and finisher (15 WOA).
Nasal swabs were pooled and evaluated via RT-PCR, while individual sera were tested for spike-specific IgG via ELISA to evaluate immune profiles alongside viral shedding.
Key Findings Across Production Stages
Analyzing viral shedding alongside antibody titers uncovered several critical dynamics:
- A Susceptibility Dip in the GDU: All GDU stages tested 100% PCR-positive, proving continuous viral circulation in gilt development. However, grower gilts (9–12 WOA) experienced a sharp drop in antibody levels compared to nursery gilts, marking this age window as a primary gap in immune protection before active immunity matures.
- Parity Gaps and Farrowing Shedding: P2 sows exhibited nearly threefold higher antibody levels than P1 sows, consistent with cumulative exposure over time. Furthermore, while gestating and weaning sows tested PCR-negative, 67% of farrowing dams shed virus, highlighting a critical transmission window in the farrowing house.
- Early Suckling Exposure: Newborn piglets were 100% PCR-negative, but 50% of wean-age piglets (3 WOA) tested positive. Wean-age pigs also had the lowest antibody levels of all downstream groups as maternal immunity waned, confirming infection occurs prior to weaning.
- Nursery Surge and Persistent Shedding: Nursery pigs (6 WOA) experienced a massive humoral immune response (highest overall antibody levels) alongside 100% PCR positivity, signaling heavy viral challenge. Notably, nasal viral shedding remained at 100% through the finishing stage (15 WOA).
What Does This Mean for Producers?
Reicks points to three practical management takeaways for swine producers and veterinarians.
- Target the Early GDU Window: Interventions such as controlled acclimation or future vaccines should focus heavily on the grower phase (9–12 WOA) to close the immunity gap before gilts enter the breeding herd.
- Tighten Farrowing Management: Because farrowing sows shed virus and suckling piglets are readily exposed, management practices that limit piglet movement—such as minimizing cross-fostering, eliminating nurse-on/nurse-off practices, and curbing foot traffic—can reduce early transmission.
- Account for Prolonged Shedding: Viral persistence from nursery through finishing means PoAstV4 circulates continuously. Herd closure protocols, internal pig flow, and replacement entry quarantine timelines must account for this extended clearance window.
For his work on this project, Reicks was selected as one of seven finalists for the Morrison Swine Innovator Prize at the Allen D. Leman Swine Conference, where he presented these findings to industry leaders and veterinarians.
