PEDV and other pathogens survive in feed for weeks

In 2013-2014, infection of pig farms with porcine epidemic diarrhea virus (PEDV) was a frequent event, even on farms using the highest level of biosecurity. In an effort to determine how this could happen, Scott Dee, DVM, began investigating.
calendar icon 13 October 2017
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“One common denominator across many of these farms was the occurrence of a feed outage in a specific subpopulation of animals, requiring an emergency feed delivery to a specific bin onsite,” Dee said in a presentation at the American Association of Swine Veterinarians annual meeting. [1]

The pigs consuming the feed from the emergency delivery were the first to become infected. Samples from inside the suspect feed bins were collected and sent to a diagnostic lab for testing. The results showed the feed did contain live PEDV, an outcome that had not been confirmed before.
Thus began a quest for answers by Dee and the team at Pipestone Applied Research, along with scientists from South Dakota State University (SDSU) including professors Eric Nelson and Diego Diel, which continues today. Their search has expanded to include the survival of high-risk viruses and the potential dangers of imported feed ingredients.

PEDV thrives in soybean meal

Dee’s first study immediately after the outbreak looked at what feed ingredients supported the PEDV virus. Various ingredients were inoculated with the virus and cultured over time. They found PEDV lived best in soybean meal where it survived for 180 days. Dee said this does not mean soybean meal is the ingredient originally contaminated with the virus. However, if the virus is in contact with meal, it can survive.

“Our experiences in China allowed us to learn about PEDV, long before the problem in the US,” Dee said. “Several of my colleagues had noticed that many of the feed ingredients on the infected farms had been imported from China.” Because the prototype strain from the US closely matched a virus from China, it was clear that a transboundary infection had occurred.

Until this diagnosis, Dee added, nobody believed a virus in feed ingredients could survive the rigors of a trip across the ocean. Dee and the Pipestone vet team decided to prove the theory.
Once again, they went to the team at SDSU and asked them to help simulate a trip that feed ingredients travel — from Beijing to Shanghai to San Francisco to Des Moines. Feed ingredients shipped from China were inoculated with PEDV, put in small containers and placed in an environmental chamber at the university.

The chamber’s computer was programmed to adjust temperature and humidity based on the actual weather for the winter of 2014. The simulation ran for 37 days, the actual length of shipping time from China. At the end of the simulation, testing confirmed PEDV was alive in the samples of soybean meal, lysine, choline and vitamin D.

High-risk viruses survive in feed

Dee said the team then wondered what other high-risk viruses around the world could survive in feed to infect US hogs through imports.

Dee sought help from Dr Paul Sundberg of the Swine Health Information Center. The center had identified 10 high-risk viruses for swine that could be devastating to the US swine industry if an outbreak occurred. Dee also wanted to do simulation testing on these viruses, to check their viability in feed ingredients over time. Many of these viruses pose a risk when used in tests. Fortunately, surrogate virus strains are available for some of the most dangerous viruses. A surrogate has familial relationships and structural similarities to foreign animal-disease virus but does not produce the disease. For example, surrogate viruses have been used to simulate disease conditions like foot-and-mouth disease (FMD).

The simulated testing on the 10 high-risk viruses is underway, using the same testing method as used on PEDV. Currently, simulations using surrogate viruses have been conducted on FMDV, hog cholera and pseudorabies. Other viruses either under evaluation or planned for evaluation in feed include vesicular stomatitis, vesicular exanthema, Nipah virus, porcine reproductive and respiratory syndrome 174 virus, porcine circovirus type 2 and swine vesicular disease.

Recently, scientists from Kansas State University have joined the team and will be evaluating the ability of African swine fever to survive a trans-Atlantic simulation in the Biosecurity Research Institute.

Assessing potential infection threat

The early results of Pipestone’s work with the high-risk virus viability in feed ingredients are surprising because, prior to this work, the risk of feed was unknown.

“These preliminary results suggest that a subset of contaminated feed ingredients could serve as vehicles for foreign animal-disease introduction to the US,” Dee said. “Of particular interest is the consistency of virus survival in soy-based products as well as the inability of virus alone to survive in the absence of a feed matrix.”

When the virus testing is completed, Dee hopes to start discussions with veterinarians, feed industry experts and government officials to develop a plan to reduce the risk of disease transmissions.
“It is time for discussions on how to adequately treat feed, how to increase biosecurity at the port level, as well as where to purchase biosecure ingredients,” Dee said.

The end result should be “a lowered incidence of feed-related disease transmission around the world,” he concluded.

[1] Dee S. What are the feed risks from biologics?, Feed: Commanding New Focus. 48th American Association of Swine Veterinarians’ Annual Meeting. 2017;3-5.

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