“If you talk to vets in the US they will probably rank contaminated transport and vehicle movement as the top risk factors, followed by feed and airborne transmission,” he told FeedNavigator.
Dr Dee was lead researcher in the study published this week, which, after months of speculation, confirmed that feed can be a vehicle for PEDv. It did this by collecting feed samples from infected farms.
Porcine plasma in the clear?
Interestingly, the feed source did not contain animal by-products, suggesting that contamination may have occurred post-processing, and potentially ruling out porcine plasma as a source of the virus.
“This study did not involve porcine plasma. The diets from the farms we studied did not contain any animal by-product. I think it is possible to feed animal plasma to pigs,” said Dr Dee.
This finding will come as welcome news to feed producers who have been defending the inclusion of porcine ingredients in feed.
A trans-state epidemic
Since its initial detection in May 2013, PEDv has spread rapidly throughout the US swine industry, with 6317 cases being confirmed in 29 states by May of this year.
Infected pigs, contaminated transport, PEDv positive aerosols and contaminated feedstuffs had been identified as potential risk factors.
While an initial report from the Canadian Food Inspection Agency indicated that consumption of PEDv-positive porcine blood plasma caused the disease in pigs, a follow-up study could not demonstrate that the feed pellets containing the blood plasma in question were capable of causing disease.
Now, the team at Pipestone Veterinary Services have provided “proof of concept” that contaminated complete feed can serve as a carrier for PEDv.
At the beginning of January, PEDv was diagnosed in three breeding herds in Iowa and Minnesota. During an investigation into the possible routes of viral entry, a consistent observation common to all three herds was noted: at the beginning of January all three farms had experienced an unexpected feed outage which had required an emergency delivery. This was deposited into a designated storage bin which fed a subpopulation of the herd. Symptoms of PEDv became apparent only in the animals that had consumed this feed.
Paint rollers were used to collect samples from the at-risk feed bins on each farm. These tested positively for the presence of PEDv RNA at the South Dakota State University Animal Disease Research and Diagnostic Laboratory.
A treatment group of three-week old piglets were allowed to consume the feed via natural feeding. Clinical signs of PEDv infection (vomiting and diarrhea) were observed, with virus and microscopic lesions detected in intestinal samples.
To understand, not to blame
“We successfully detected PEDv RNA in complete feed material across all three sites and proved its infectivity using natural feeding behaviour, a novel finding not yet reported,” wrote the researchers.
However, Dr Dee was anxious to emphasise that the study was carried out “to understand the risks not to blame the feed industry” and said he thought that producers would be able to “do a better job of viral security” on the back of the findings.
He added: “People will understand now that feed can become contaminated during post-processing. We’re doing some work on trying to reduce the feed contamination risk. Those data will be published in the near future.”
Carrier not source
Responding to the study, the American Feed Industry Association (AFIA) stressed the importance of differentiating between a ‘carrier’ and a ‘source’.
“It’s important to note that being a carrier of the virus does not mean that feed is the source. The prevalence of the disease on an infected farm can contaminate many items,” said Richard Sellers, AFIA’s senior vice president of legislative and regulatory affairs, in a statement.
Source: BMC Veterinary Research 2014; 10:176
“An evaluation of contaminated complete feed as a vehicle for porcine epidemic diarrhea virus infection of naïve pigs following consumption via natural feeding behavior: proof of concept”
Authors: Scott Dee, Travis Clement, Adam Schelkopf, Joel Nerem, David Knudsen, Jane Christopher-Hennings and Eric Nelson