SHIC-Funded Porcine Sapovirus Research Isolates Field Strains from US Herds

Porcine sapovirus (PoSaV) is an emerging pathogen that causes diarrhea in suckling and weaned pigs. Accurate detection and isolation of circulating PoSaV strains is needed to characterize infection and develop preventative strategies. To help advance PoSaV research, the Swine Health Information Center funded a study conducted by Dr. Qiuhong Wang at The Ohio State University and Dr. Thomas Petznick at Veterinary Health Services, Omaha, Nebraska. Recently published findings in the journal Veterinary Microbiology detail the successful isolation of contemporary PoSaV field strains from US swine herds, an essential milestone that could lead to more effective diagnostic tools and future vaccine development.  

PoSaV is a very environmentally stable virus that can persist and spread within swine herds, making it a challenging issue especially in high-health production environments. This SHIC-funded study addresses gaps in PoSaV knowledge and has objectives to improve understanding of the virus, provide tools for diagnosis, and develop potential mitigation strategies, such as vaccines, for PoSaV infection control. Overall goals of advancing PoSaV knowledge are to reduce potential economic losses associated with post-weaning diarrhea, reduced weaning weight, and poor growth performance in US swine. 

Find the complete paper here: Aryal, B., et al., 2025, Veterinary Microbiology. doi.org/10.1016/j.vetmic.2025.110709 

Sapoviruses belong to the Caliciviridae family, a group of non-enveloped viruses known for infecting a range of animal species, including pigs and humans (Oka et al., 2015). Among the many genogroups identified, GIII PoSaV is the most common genogroup found in pigs worldwide (Lyoo et al., 2020). Infected pigs, particularly those in the weaning and post-weaning stages, can show mild to moderate diarrhea or remain clinically healthy while shedding the virus in feces (Kuroda et al., 2017). 

Though PoSaV infections are generally self-limiting, studies have shown that affected piglets may suffer a loss in expected weaning weight of roughly 1.0 – 2.0 pounds per head (Shen et al., 2022). These seemingly small performance gaps can add up significantly across large production systems. Co-infections with other enteric pathogens, such as rotavirus, swine enteric coronaviruses, and Escherichia coli, may worsen clinical signs and further erode productivity. 

Historically, the growth and culture of PoSaV outside the animal host has been a challenge. Only two older reference strains, Cowden and LL14, had been successfully propagated in laboratory cell lines, and both required the presence of bile acids to replicate (Chang et al., 2004). Lacking consistent isolation systems, the study of current field strains and the ability to design targeted control measures have been limited. 

Due to the increasing association of PoSaV with diarrhea in young pigs, underdiagnosis of field cases, and the lack of progress in propagating the virus, a primary objective of this study sought to isolate contemporary PoSaV strains and develop tools to perform cell culture isolation of circulating PoSaV. To conduct this study, five sow farms in Nebraska were sampled that had piglets exhibiting PoSaV-suspected gastroenteritis outbreaks. Samples were collected between November 2023 – May 2024 from piglets 12 to 28 days of age with clinical signs of diarrhea. A total of 35 fecal and seven small intestinal samples were obtained for testing.  

All samples were evaluated for the presence of PoSaV GIII by PCR. Molecular PCR screening revealed that 60% (25/42) of the samples were positive for GIII PoSaV, confirming a significant presence in the herds. Four of five farms tested positive for PoSaV based on PCR results, with detection rates of 33% – 100%. Detection of GIII PoSaV from the samples in this study indicates that GIII continues to be the main genogroup in suckling and post-weaning pigs. The 60% prevalence of PoSaV in the clinically affected pigs is consistent with previous findings, providing evidence that PoSaV could be a major enteric pathogen responsible for diarrhea in younger piglets. However, diagnostic testing was not performed for the detection of other enteric viruses such as rotavirus or astrovirus.  

To further characterize the viruses detected, one representative PCR-positive sample (Ct < 20) from each of the four farms was selected for NGS. Based on near-complete nucleotide sequences and amino acid sequences of non-structural proteins, three of the samples from three different farms were similar, suggesting a shared more recent common ancestor. However, the sample from the fourth farm branches separately suggesting it may have undergone evolutionary changes that differentiate it from other strains. The four virus strains are genetically similar but are different from classical reference strains, indicating potential evolutionary changes. These findings emphasize the need for continued surveillance and molecular characterization of identified strains. 

In addition to the genetic characterization, the investigators achieved successful virus isolation in two different porcine cell lines, LLC-PK1 (porcine kidney) and ST (swine testicular), marking the first-ever propagation of PoSaV strains in ST cells. Out of the 25 positive samples, 8% grew in ST cells and 16% in LLC-PK1 cells. No isolates were recovered in the IPEC-J2 intestinal cell line, even though it had previously been used successfully with historic strains. 

The ability to culture PoSaV in the cell lines within this study provides immediate and long-term potential benefits for the pork industry, such as improved diagnostic tools. Further, the discovery that ST cells can support PoSaV growth could accelerate the future development of a commercial PoSaV vaccine. Having live isolates means researchers can refine PCR assays specific to the strains currently circulating in North American farms. More accurate diagnostics help veterinarians distinguish PoSaV from other causes of diarrhea, improving treatment and biosecurity decisions. Researchers plan to study the pathogenesis of these new isolates in greater depth and explore how different environmental or management factors might influence viral persistence within herds. 

Better understanding of PoSaV biology gives the industry new tools to diagnose, monitor, and manage swine enteric health more precisely, helping ensure pigs transition more smoothly through weaning and maintain consistent growth. Developing new knowledge and tools for PoSaV aligns with SHIC’s mission to mitigate emerging disease threats and protect the health of the US swine herd.