SHIC Supported Genetic Analyses Conducted on Recent Strep Cases in US Assembly Yards

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) was isolated from two recent cases of high sow and feeder pig mortality in US assembly yards. While this organism is a sporadic cause of disease in multiple animal species, it has rarely been associated with disease outbreaks in US swine. Work completed by the Iowa State University Veterinary Diagnostic Lab (ISU VDL) since the initial diagnosis, with support from the Swine Health Information Center (SHIC), provides more details on current concerns.

See the initial report on this occurrence of S. zooepidemicus here.

Based on review of past cases, ISU VDL learned the recent US strains are strikingly similar to the ATCC strain isolated from swine outbreak(s) of high mortality in China in the mid-1970s that reportedly involved the loss of more than 300,000 pigs ^{(1, 2)}. These further characterization results suggest these recent case series for US assembly yards were related and caused by the same variant of S. zooepidemicus. Previous isolations of S. zooepidemicus from clinically ill pigs have been rather limited in the US. There is minimal information concerning the novelty of this particular variant of S. zooepidemicus, as compared to past findings in US swine.

Elevated swine mortalities in western Canadian assembly yards due to S. zooepidemicus were reported in the second quarter of 2019, per the Canadian West Swine Health Intelligence Network. More recently, an additional incident of elevated mortality and abortions caused by S. zooepidemicus in four related commercial sow farms located in Manitoba, Canada, occurred. The S. zooepidemicus isolate from the case series involving the four commercial sow farms in Manitoba was also reported to be genetically similar to the aforementioned ATCC strain of S. zooepidemicus associated with the high swine mortality event in Sichuan province in China in the 1970s⁽³⁾.

These occurrences in the US and western Canada should spur increased pig farm biosecurity efforts, particularly related to transport and collection points.

SHIC will continue its efforts as further study is needed to better understand the relevance and prevalence of S. zooepidemicus in North American swine.

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