Diarrhea. It’s beyond frustrating. It reduces performance, causes dehydration and can lead to high mortality. It costs producers money and time. In the past few years, an emerging pathogen, porcine sapovirus (PoSaV), has been identified as a significant cause of piglet diarrhea.
PoSaV is challenging to differentiate from other viruses like porcine epidemic diarrhea (PED), delta coronavirus and transmissible gastroenteritis, says Lisa Becton, DVM, associate director of the Swine Health Information Center. 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. The virus is environmentally stable so it can spread quickly in a herd.
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 to 2.0 lb. per head, SHIC reports. These “seemingly small performance gaps” can add up quickly 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 decrease productivity.
“The problem with PoSaV is that there has been, up until recently, very limited mechanisms to grow and propagate the virus,” Becton says. “That is very important if you want to continue to further your diagnostics – if you want to actually grow the virus in cell culture or for development of vaccine.”
Accurate detection and isolation of circulating PoSaV strains is needed to not only characterize infection but also develop preventative strategies.
Porcine Sapovirus Research Isolates Field Strains from U.S. Herds
A recent study published in Veterinary Microbiology conducted by Qiuhong Wang at The Ohio State University and Thomas Petznick, DVM, at Veterinary Health Services in Omaha, Neb., details the successful isolation of contemporary PoSaV field strains from U.S. swine herds.
In this study, five sow farms in Nebraska were sampled that had piglets exhibiting PoSaV-suspected gastroenteritis outbreaks. Samples were collected between November 2023 through 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% of the samples were positive, confirming a significant presence in the herds. Four of five farms tested positive for PoSaV based on PCR results, with detection rates of 33% to 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,” SHIC reports. “However, diagnostic testing was not performed for the detection of other enteric viruses such as rotavirus or astrovirus.”
Further characterization of the samples showed 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. These findings emphasize the need for continued surveillance and molecular characterization of identified strains, SHIC reports.
Deciphering Diarrhea
“This study furthers our understanding of PoSaV as an emerging disease,” Becton says. “It fills gaps in knowledge and technologies that we have not had to date, with the goal to help reduce and mitigate the impact. If we can grow the virus and understand and characterize it better, that could lead us to improve diagnostics as well as vaccine alternatives or options.”
Viruses adapt very well to their host, Becton points out. When a virus infects the gut of a pig, it’s very specific for that environment and has very specific growth requirements for entry into the cells.
“When you try to replicate that model of a pig’s intestines outside of the pig, it gets very difficult, because the viruses may not always want to adhere or get into the cells like they would under normal or natural situations,” she adds. “There can be biochemical changes with how the virus responds to other cells. There are different functions within the pig that are very hard to mimic outside of the pig.”
This is why Wang and Petznick’s PoSaV study is so encouraging to the swine industry.
“It gives us opportunity to do a deeper dive into what’s causing baby pig diarrhea,” Becton says. “If we can understand that better, and accurately diagnose what the causative agent is, then we can come up with a different plan on how to manage it.”
