Progress on Feed Biosecurity Research Validates Sampling Methods and Evaluates Presence of SVA in Feed Across US Feed Mills

October 24, 2018 — Paul Sundberg

Figuring out feed biosecurity is a priority and data from Swine Health Information Center (SHIC)-sponsored research continues to arrive. While feed has been demonstrated as a potential vector for bacteria and viruses, there is no approved method for its evaluation. Validating feed testing methodology is a focus for SHIC. Recently completed work by Dr. Cassandra Jones from Kansas State University validates standardized dust swabbing techniques as means of detection for Seneca Virus A (SVA) at feed mills albeit with less precision than directly analyzing feed samples. Of particular interest, she also simultaneously determined the prevalence and distribution of SVA in United States swine feed mills, as an indicator of risk of domestic and foreign animal disease transmission through feed. The good news: Prevalence for SVA is low in US feed mills. But, where SVA was found on feed mill worker shoes, a farm that mill fed went positive for SVA after detection.

Why is feed mill detection important for SVA in particular? Not only is SVA considered a surrogate for Foot and Mouth Disease (FMD); from October 2014 to March 2016, the Brazilian swine industry experienced idiopathic vesicular disease and epidemic transient neonatal losses, two emerging disease syndromes associated with SVA, in up to 80% of their industry. Transmission was positively associated with pelleted feed (Defra, 2016). Recent research sponsored by SHIC shows that feed-based transmission routes may be a risk for both domestic and foreign animal disease entry into the U.S. swine herd (SHIC, 2017). As an example, SVA can survive for up to 37 days in animal feed ingredients (SHIC, 2017). Once present, viruses in feed, feed ingredients, and feed mills are difficult to mitigate. Also, research shows that when Porcine Epidemic Diarrhea Virus (PEDV) enters a feed mill, infectious viral particles spread rapidly to all surfaces, making decontamination tough and heightening the risk for feed transmission (Gebhardt et al., 2017; Huss et al., 2017).

Dr. Jones' research demonstrated that feed sample type impacted 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. 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. In summary, swab samples did work for SVA, but feed samples were better.

Five of 375 samples analyzed positive for SVA, with Ct ranging from 37.4 to 39.9. One positive sample was collected in late fall. The other four positive samples were collected in winter. No positive samples were identified in summer. Where were they found? Two samples were from load-out augers, one from fat intake inlet, one from floor dust, and of note, one was from worker shoes.

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.

Funded by America's pork producers to protect and enhance the health of the US swine herd, SHIC focuses its efforts on prevention, preparedness, and response. As a conduit of information and research, SHIC encourages sharing of its publications and research for the benefit of swine health. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at psundberg@swinehealth.org.

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Paul Sundberg, Executive Director, Swine Health Information Center