Further evidence contaminated feed ingredients are risk for transport of pathogens

By Aerin Einstein-Curtis

- Last updated on GMT

© GettyImages/Patarapong
© GettyImages/Patarapong
Feed and feed ingredients traveling across Atlantic or Pacific trade routes may have the ability to carry unwanted swine diseases, including the African Swine Fever Virus, say researchers.

Building off of initial work done to track if the Porcine Epidemic Diarrhea virus (PEDv) could be transported in feed, a group of researchers from multiple academic and research institutions in the US examined 11 additional viruses based on their score on the Swine Health Information Center’s swine disease matrix​. The group published its work in the journal Plos One​.

One disease focused on in the project was African swine fever virus (ASFV) because of the risk presented by the disease, said Megan Niederwerder, co-author and an assistant professor of diagnostic medicine and pathobiology at Kansas State University. The disease is considered one of the top three risks for the US swine industry.

“Since 2007, ASFV has spread into Eastern Europe and Russia, increasing the risk of ASFV introduction into other parts of the world, such as the US,”​ she told FeedNavigator. “There are currently no commercial vaccines available for ASFV, making disease control a significant challenge once the virus is introduced. Additional challenges associated with control of ASFV include the potential to become endemic in feral swine as well as soft ticks.”

The disease was one of several that the group examined for its ability to survive the process of being transported accidentally into the US through feed, feed additives or other imported products, said Niederwerder. “We expected that individual viruses would have varying survival dependent on environmental stability and feed ingredient matrices,”​ she added.

“One unique finding with regards to ASFV was the ability to survive the simulated trans-oceanic voyage in the absence of a protective feed matrix,” ​she said. “ASFV was the only virus tested with this characteristic.”

The disease also was found to survive in conventional and organic soybean meal, soy oil cake, choline and the complete feed, the researchers added.

Historically, the impact of foreign animal diseases (FADs) on global livestock production and economics has been devastating.

In 1997, Taiwan and the Netherlands experienced outbreaks of Foot and Mouth Disease (FMD) and Classical Swine Fever (CSF), respectively. In Taiwan, the estimated cost of the FMD outbreak was $379m, due to the slaughter of over four million pigs, approximately 40% of the country’s pig population at the time. In addition, $1.6bn was lost due to a trade ban of pork to Japan.

In the Netherlands, the CSF outbreak resulted in the slaughter of 700,000 pigs across 429 infected farms and the pre-emptive depopulation of 1.1m pigs from an additional 1,300 farms.

In 2001, the FMD outbreak in the UK resulted in the slaughter of seven million animals, with an overall impact of $11.9-$18.4bn, including a $4.8bn loss to agriculture, the food industry and the public sector, $4.2-$4.9 bn in losses to the tourism sector and an additional $2.9-$3.4bn in indirect losses.

While the US has remained free of FMD and CSF over the past several decades, projected losses should an outbreak occur in the country range between $12.9-$14 billion for FMD and $2.6-$9.6 billion for CSF. In addition, the estimated impact of the introduction of African Swine Fever Virus (ASFV) to the US would cost $16.5bnn during the first year of the outbreak.

ASFV is a highly contagious pathogen that threatens the swine industry worldwide. Its recent introduction to the Caucasus region and subsequent spread into Eastern Europe, the lack of an effective vaccine, and the role of wild boars and soft ticks in transmission and maintenance of the virus underscores the significance of ASFV and the challenges to disease control.

The introduction of Porcine Epidemic Diarrhea Virus (PEDv) into the US in 2013 serves as an example of the impact that exotic diseases may have on the US livestock industry. The introduction of the virus into the US resulted in the loss of about seven million pigs or 10% of the annual pig population.

Evaluating diseases and findings

In addition to ASFV, there were 10 other viruses or their surrogates considered during the trial, said the researchers. Surrogate viruses provided similar genetic and physical properties and belonged to the same virus family.

The other diseases studied included: “Foot and Mouth Disease Virus (FMDV), Classical Swine Fever Virus (CSFV), Influenza A Virus of Swine (IAV-S), Pseudorabies virus (PRV), Nipah Virus (NiV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Swine Vesicular Disease Virus (SVDV), Vesicular Stomatitis Virus (VSV), Porcine Circovirus Type 2 (PCV2) and Vesicular Exanthema of Swine Virus (VESV),” ​they said. Six surrogates were used in the study.

Viruses were evaluated for their ability to survive either the 37-day long Trans-Pacific, or 30-day Trans-Atlantic models in relevant feeds and feed ingredients, they said. The diseases also faced changing environmental conditions.

At the end of the specified time period samples were tested for presence of the virus and its ability to be infectious, they said. Ingredients found to carry living virus included conventional soybean meal. Lysine hydrochloride, choline chloride, vitamin D and pork sausage casings.

Other feed ingredients tested included organic and conventional soybean meal, soy oil cake, dried distillers’ grains with solubles, lysine hydrochloride, vitamin D, choline chloride, moist cat food, moist dog food, dry dog food and natural pork sausage casings, said the researchers. Complete swine feed was used as a positive control and samples of the viruses in cell culture media also were used to see if the disease could survive without a feed matrix.

Feed ingredients found to support virus survival at a high frequency included conventional soybean meal, lysine hydrochloride and the complete feed, followed by vitamin D, choline chloride and sausage casings, they said.

There are some indications that higher protein levels may be more supportive of virus survival, said Niederwerder. However, more research is needed to draw conclusions about the types of feed or feed ingredients that could be more at risk to playing host to a virus.

Industry implications and looking forward

To address the challenge of the survivability of some diseases during transportation, the research group sought to publish their work, said Niederwerder.

“Publishing our findings in a peer-reviewed journal is a very important step, not only to communicate this research to the greater scientific audience but also to have this research formally evaluated for its quality and validity,” ​she said.

"This information should increase awareness about feed biosecurity and the potential for feed and feed ingredients to serve as routes for virus introduction and transmission,”​ she added.

Questions remain around the infectious dose of ASFV when the disease is present in feed, said Niederwerder. The team said there is a need to find ways to mitigate the disease when it is present in feed or a feed ingredient.

“We are currently investigating several feed additives for their ability to mitigate or inactivate viruses, including ASFV, in feed or feed ingredients,” ​she said. “If found effective, these mitigants could hypothetically be added in the country of origin or in the US to reduce the risk of virus introduction and transmission through feed.”

Additional research also is ongoing to expand understanding of the information generated in the initial project, she said. “We have two studies currently ongoing that build on our initial work,”​ she added.

“First, we are determining the infectious dose of ASFV when consumed in feed,” ​she said. “Second, we are investigating the ability of several potential mitigants to inactivate ASFV in feed and feed ingredients.”

Source: Plos One

DOI: doi.org/10.1371/journal.pone.0194509

Title: Survival of viral pathogens in animal feed ingredients under transboundary shipping models

Authors: S Dee, F. Bauermann, M. Niederwerder, A. Singrey, T. Clement, M. de Lima, C. Long, G. Patterson, M. Sheahan, A. Stoian, V. Petrovan, C. Jones, J. De Jong, J. Ji, G. Spronk, L. Minion, J. Christopher-Hennings, J. Zimmerman, R. Rowland, E. Nelson, P. Sundberg, D. Diel

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