Research Confirms Seneca Virus A in Feed, Validates Sampling Methods
November 14, 2018 —
Feed biosecurity is on the minds of many as threats of foreign animal disease (FAD) outbreaks continue to make headlines across the country. New research by the feed safety team at Kansas State University demonstrates that Seneca Virus A (SVA), which is also a surrogate for foot and mouth disease, is present in U.S. swine feed mills and validates standardized dust swabbing techniques as means of SVA detection. [Source: Pork, November 9, 2018, by Jennifer Shike]
"The feed supply chain can be a source of SVA into farms, but it is not always directly through feed," says Cassandra Jones, associate professor in animal sciences at Kansas State University and lead researcher on the project.
A number of individuals with multiple farm contacts comingle at a feed mill, creating a risk for biosecurity breaches to occur, including potential SVA transmission through feed, feed transportation, or individual's shoes.
The research showed that the virus is not widespread in mills, as only 5 of the 375 samples were positive for the virus. However, mills that were part of the study were not believed to be feeding SVA-positive herds at the time of sampling.
Positive samples were mostly found in load-out augers, floor dust, a fat intake inlet, and a worker shoe, Jones says. Once present, viruses in feed, feed ingredients, and feed mills are difficult to mitigate.
"Understanding that the feed mill may be a risk for SVA is important to limit the spread of the virus into farms," Jones adds. "SVA was not widespread throughout the swine feed mills analyzed in this experiment, but its presence in a mill may be indicative of disease risk or entry into pig populations, particularly through worker shoes. A sow farm being fed by the mill with SVA on worker shoes was subsequently diagnosed with SVA after the sample was collected."
Prior to K-State's research, there was not a validated method for sampling or analyzing samples in feed or from feed mill surfaces.
Jones demonstrated that feed sample type does impact the quantity of detectable SVA. Results are reported as the quantity of detectable SVA as determined by threshold cycle (Ct) in qRT-PCR. When the Ct is higher, we are less likely to detect virus, she says. Feed samples were approximately 8 Ct higher than the inoculum, and swab samples were approximately 4 Ct higher than feed.
The research showed that an environmental swab can be used to detect SVA but with 4 Ct less precision than analyzing feed samples direct. A freeze/thaw cycle did not impact detectable SVA compared to samples that were analyzed immediately.
Swab samples work to detect SVA, and with a greater probability of detection than product sampling.
"In the end, producers and feed manufacturers should be aware that the feed mill can be a source of pathogens, both through feed, but also its transportation," she says. "We must extend biosecurity practices from farms to feed mills, such as limiting foot traffic and better controlling dust."
Jones' research was funded by the Swine Health Information Center (SHIC), and was in collaboration with Megan Niederwerder, Jason Woodworth, and Steve Dritz.
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