Josepha DeLay, Davor Ojkic

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2023;27(1):15.

Porcine sapovirus (PSaV) has been associated with diarrhea in pigs of all ages, commonly in mixed infection with other viral, bacterial, and / or protozoal pathogens.  The virus has been detected in swine worldwide, and in both symptomatic and asymptomatic pigs, although a recent study has demonstrated higher viral loads in animals with clinical diarrhea.  PSaV was first detected in 1980 in the United States in a diarrheic piglet co-infected with rotavirus and another undetermined virus.  Subsequently, enteritis was experimentally reproduced in gnotobiotic piglets orally infected with the virus.

PSaV is a member of the Calicivirus family.  Currently, 8 genogroups of the virus are known, and genogroup III is predominant.  Recombination within and between genogroups, and genetic drift are common viral adaptation strategies among sapoviruses.  It should be noted that PSaV is distinct from the similarly named porcine sapelovirus (PSV) which causes neurologic disease in pigs.

Recent research has indicated that PSaV may be an emerging pathogen, and in some herds, can be a significant contributor to enteric disease in young pigs.  Using whole genome sequencing, PSaV has been identified in feces from pigs of various ages with clinical diarrhea, often in mixed infection with other enteric pathogens, but occasionally as the sole pathogen identified. 

PSaV has recently been detected in nursing piglets with diarrhea from an Ontario herd.  The piglets were negative for other common enteric pathogens (rotavirus, PEDV, PDCoV, TGEV, bacteria, coccidia) based on PCR, culture, and histopathology results.  Histologic features of sapovirus enteritis are similar to those of other enteric viruses (rotavirus, porcine coronaviruses), characterized by villus atrophy and epithelial attenuation at villus tips.  In experimental infections, the anatomic distribution of lesions differed from other enteric viral pathogens in that lesions were most prominent in duodenum and less severe in jejunum and ileum.  Similar distribution has not been described in recent literature reports of natural infections.

Knowledge of the relative importance of PSaV in swine enteric disease is still incomplete.  A potential role for the virus should be considered in swine diarrhea cases, especially in nursing and weaned pigs, and when other enteric pathogens are not detected.  Currently, testing for PSaV by PCR and in situ hybridization (ISH) is carried out at a laboratory external to the AHL.  However PSaV PCR is being developed and will be available at the AHL in the near future.  PSaV can be detected in both symptomatic and asymptomatic swine, and mixed infections with other pathogens are common.  With these features in mind, it is important to interpret PSaV test results in the context of test results targeting other common enteric pathogens.  Formalin-fixed samples for histopathology should include duodenum, as well as jejunum, ileum, and colon, due to the predominance of duodenal lesions noted in experimental PSaV infections.   AHL

Reference

1. Nagai M et al. Porcine sapoviruses: Pathogenesis, epidemiology, genetic diversity, and diagnosis. Virus Res 2020; https://doi.org/10.1016/j.virusres.2020.198025 [1]