How did PEDv enter the U.S.? Simulation provides insight

Industry experts are certain the first strain of Porcine Epidemic Diarrhea virus (PEDv) identified in the U.S. came from China, but no one is sure how the disease got here. Dr. Scott Dee, DVM, with Pipestone Applied Research in Pipestone, Minn., headed an interesting research study designed to simulate the shipping route of a feed source from Beijing, China to Des Moines, Iowa.

"The purpose of this study was to develop a model to evaluate the transboundary risk of PEDV-contaminated swine feed ingredients during a simulated shipment from China to the U.S., as well as test the effect of two mitigation strategies," Dee said. "The study was based on the hypothesis that while select non-treated ingredients could provide a protective effect on PEDV survival, mitigation would reduce risk."

During a presentation at the 2016 American Association of Swine Veterinarians meeting, Dee said one feature that was consistent across several of these ingredients was that they are imported to the U.S. from China. As the original PEDv detected in the U.S. is closely related to a Chinese variant, it raises the question whether contaminated feed ingredients imported from China could have served as a source for viral entry to the U.S. in 2013.

"During the widespread epidemic, the role of feed in transboundary spread of the virus was downplayed, based on lack of data supporting survival of PEDv in feed ingredients over time and under conditions representative of trans-oceanic transport. Recently, extended survival of PEDV in individual feed ingredients under wintertime ambient conditions has been reported. Most notably, survival of PEDV was demonstrated in soybean meal for 180

days, along with evidence of virus survival in lysine hydrochloride, choline chloride, DDGS and several porcine by-products for at least 30

days."

"This project is not anti-China or anti-feed industry," Dee said. "It is a collection of objective data using a novel mechanism approach and justification for future research, and it starts the conversation on how to protect our industry in the future."

Dee put samples in an environmental chamber with relative humidity to mimic a trip from Beijing to Des Moines. The simulated route of shipping would start in Beijing, then travel to Shanghai where the ingredients would be held for seven days in port (for shipment preparation), then it would travel for 17 days across the Pacific Ocean. It would port in San Francisco and be there another seven days to clear customs. It would then be transported for two days to Des Moines, where it would remain for three days. This would allow for a typical total transit period of 37 days.

To simulate the environmental conditions that cargo would encounter during this trip, Pipestone used an instrument called an environmental chamber that can reproduce temperature and humidity fluctuations on a daily basis.

Researchers then imputed historic weather data that reflected the period of December 2012 to January 2013, before clinical signs of PEDv were first reported (April 2013).

Small, plastic baby food containers held standard quantities of different ingredients, which were contaminated with equal levels of PEDv.

Dee said the ingredients were screened by PCR test to ensure a PEDv-negative status prior to the onset of the study. The treatments for the study were a liquid antimicrobial (LA), which was SalCURB from Kemin Industries, or a 2% custom medium chain fatty acid blend (MCFA). Control ingredients were treated with sterile saline.

Samples were organized into 1 of 4 identical batches, each representing a specific segment of the 37-day shipping period, with 90 total samples per batch. The entire study was done in an environmental chamber to simulate each day and how the temperature might change during that day. Batches were removed accordingly.

Both the liquid antimicrobial and the MCFA appeared to have an equivalent effect on virus viability, reported Dee. "This outcome supports the validity of chemical mitigation as a means to reduce the risk of PEDV in feed ingredients stored under conditions modeling the trans-oceanic voyage, as well as provides options for treatment.

"Under the conditions of this study, PED survived a simulated trans-Pacific voyage from China to the U.S. in feed; and a subset of ingredients demonstrated a 'protective effect' in the face of a robust environment challenge," Dee said. "These data provide the initial proof of concept that select contaminated feed ingredients could have served as vehicles for PEDv entry into North America. Feed should now be considered both a domestic and a transboundary risk factor for infections agents.

Pipestone Applied Research will continue to focus on PEDv transmission and how the U.S. industry can prevent, or better prepare for, future outbreaks of transboundary foreign animal diseases, such as Foot and Mouth Disease and Hog Cholera.

"Future studies should include transboundary foreign animal disease survival using surrogates; sampling strategies for high-risk ingredients and sites; and mitigation strategies," Dee said.

For questions on the trial, contact Dr. Scott Dee at 507.825.4211 or at[email protected].

 
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