Level of ASF virus required to cause infection in liquid extremely low
The K-State study is the first to demonstrate that African swine fever can be easily transmitted through the natural consumption of contaminated feed and liquid.
February 14, 2019
A Kansas State University researcher has published a study confirming experimental transmission of African swine fever virus through feed.
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 could spread in feed and feed ingredients. A new publication details the dose necessary to transmit the disease when pigs ingest virus-contaminated feed or liquid.
“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,” Niederwerder says. “This study is the first to demonstrate that African swine fever can be easily transmitted through the natural consumption of contaminated feed and liquid.”
The study, “Infectious dose of African swine fever virus when consumed naturally in liquid or feed,” was published in Emerging Infectious Diseases. Niederwerder and collaborators found that the level of virus required to cause infection in liquid was extremely low, demonstrating the high infectivity of ASF through the oral route. Although greater concentrations of virus were required to cause infection through feed, the high frequency of exposure may 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. One common practice in China, for instance, is 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.
“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.”
Introduction of ASF virus would be devastating to U.S. swine production because it is a trade-limiting disease that causes severe clinical signs and high mortality in pigs. Another costly swine disease, porcine epidemic diarrhea virus, was introduced into the United States in 2013 and caused the death of an estimated 7 million pigs within the first year. Subsequent investigations unveiled the risk of feed for introduction and transmission of swine viruses. Niederwerder’s goal is to prevent another catastrophic disease outbreak.
Peter Dorhout, Kansas State University vice president for research, says protecting U.S. producers and consumers against disease outbreaks is an area in which the university excels.