S. zooepidemicus Research Arms Veterinarians with New Resources
In 2019, outbreaks of S. zooepidemicus (S. Zoo) septicemia were reported in Ohio and Tennessee with mortality as high as 50%. In January 2021, a sow herd in Indiana experienced abnormally high mortalities related to S. zoo, the Swine Health Information Center (SHIC) reports.
This emergence of S. zoo was associated with mortalities at a level not previously seen in the U.S. so SHIC funded a project at Iowa State University (ISU) and the National Veterinary Services Laboratory to learn more.
The result was the first study to experimentally infect and reproduce the disease in weaned pigs with a hypervirulent swine S. zoo strain, SHIC reports. In addition, pathogenicity differences between genetically different swine strains were described. The research resulted in a newly developed multiplex PCR that provides an accurate and timely assay for detecting and monitoring S. zoo in swine herds.
In the study of the 2019 outbreak, researchers characterized eight isolates associated with high mortality from Ohio and Tennessee by performing whole-genome sequencing on these eight isolates along with another outbreak-unrelated swine isolate from Arizona and 15 S. zoo isolates from other animal species. Phylogenetic analysis showed that the 2019 outbreak isolates were clustered together, but genetically distant to the outbreak-unrelated Arizona swine isolate and the isolates from the other animal species, SHIC reports.
“Three full-length complete genome sequences were further assembled, and comparative genomic analyses identified several genomic islands and virulence genes specifically in the outbreak isolates,” SHIC said in a release.
The recently completed S. zoo challenge model work evaluated the disease process and diagnostics, which provided meaningful information about the pathogenicity and epidemiology of S. zoo in pigs by challenging one group of conventional six-week-old pigs with hypervirulent S. zoo strains and another group with a genetically different, less virulent S. zoo strain. Additionally, a multiplex PCR assay was designed for S. zoo identification and prediction of virulence in swine isolates, SHIC reports.
Then in January 2021, two-year-old adult sows from a production system in Indiana experienced increased death loss. The farm reported cyanotic ears, abortion and uterine discharge and received a laboratory diagnosis of S. zoo septicemia.
These three Indiana isolates were found to be genetically distant and independent to the Ohio and Tennessee isolates, warranting further studies to determine the virulence and to understand the underlying virulence mechanisms, SHIC said in a release.
“Findings from these projects provide significant and timely insights for a better understanding of the epidemiology and virulence of S. zoo isolates, consistent with the SHIC mission. In addition, identification of specific virulence genes and genomic islands and the development of molecular diagnostic tool may provide the basis for future investigation of virulence mechanisms and control measures,” SHIC said in the release.
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