A Kansas State study confirms that African swine fever can be easily transmitted through the natural consumption of contaminated feed and liquid. This first-of-its-kind study emphasizes the critical need for feed biosecurity in the swine industry.
Megan Niederwerder, Kansas State University assistant professor of diagnostic medicine and pathobiology in the College of Veterinary Medicine, is leading a team that is exploring how the currently circulating strain of ASF, Georgia 2007, could spread in feed and feed ingredients. The team’s latest publication details the dose necessary to transmit the disease.
“Our research is the first to demonstrate that ASF can be transmitted through the natural consumption of contaminated complete feed in the absence of infectious pork products,” Niederwerder says. "Although feed and feed ingredients are a less recognized transmission route for African swine fever, the global distribution of feed ingredients makes this pathway important to consider for transboundary introduction of the virus."
Researchers discovered that the level of virus required to cause infection in liquid was extremely low, demonstrating the high infectivity of ASF through the oral route. Even though greater concentrations of virus were required to cause infection through feed, the repeated exposure could make contaminated feed a more significant risk factor.
"Working with statistician Trevor Hefley, we were able to model the probability of African swine fever infection when pigs consumed a contaminated batch of feed over time," Niederwerder says. "The likelihood of infection increased dramatically after even 10 exposures, or consumption of 1 kilogram of contaminated feed. Modeling multiple exposures increases the applicability of our experimental data to what would occur at the farm."
Agricultural processing methods for feed ingredients can put them at risk for contamination in countries with ASF. In China, it’s common to dry crops on roadways. Those roadways could be contaminated by traffic from trucks containing infected pigs. Processing ingredients on contaminated equipment is another possible source of transmitting virus particles to feed, she adds.
"Millions of kilograms of feed ingredients are imported from countries where African swine fever virus is currently circulating," Niederwerder says. "Our previous work demonstrated that a wide range of feed ingredients promote survival of the virus after exposure to environmental conditions simulating transboundary shipment."
ASF is arguably the most significant threat to worldwide swine production, Niederwerder says.
"With no effective vaccine or treatment, preventing introduction of the virus is the primary goal of countries free of the disease,” she says. “Our hope is that this research will further define possible routes of disease spread and develop mitigation strategies to prevent introduction into the U.S. swine herd."
Now that the group has confirmed ASF transmission through feed and has identified the oral dose necessary for infection, the next step will be to identify ways to reduce or eliminate this risk, including chemical additives, storage time, heat treatments or other steps.
The study, "Infectious dose of African swine fever virus when consumed naturally in liquid or feed," was published in Emerging Infectious Diseases. The National Pork Checkoff and the State of Kansas National Bio and Agro-defense Facility Fund provided funding for the study. Kansas State University co-authors on the publication include Ana Stoian, Raymond "Bob" Rowland, Steve Dritz, Vlad Petrovan, Laura Constance, Jordan Gebhardt, Matthew Olcha, Cassandra Jones, Jason Woodworth, Ying Fang, Jia Liang and Trevor Hefley.
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