African swine fever (ASF) is arguably the most significant threat to worldwide pork production due to its high case fatality rate, recent emergence in new countries and continents, lack of a commercially available vaccine and substantial impacts on global markets. Now, eight years of extensive research, including work at Kansas State University, has led to a disquieting scenario for swine producers: Feed and feed ingredients could potentially serve as means for the introduction and transmission of foreign animal diseases of swine.
Megan Niederwerder, assistant professor of diagnostic medicine and pathobiology in the college of veterinary medicine, recently published an overview on the significance of the collective feed research related to swine viruses and specifically to African swine fever (ASF) virus. "Risk and Mitigation of African Swine Fever Virus in Feed" was published March 18 in the journal Animals. Research funding was provided by the National Pork Board.
"Since the 2013 introduction of porcine epidemic diarrhea virus into the United States, researchers have investigated the potential role of feed and feed ingredients for the transboundary spread of swine diseases," Niederwerder said. "Feed ingredients are commodities traded worldwide, and the U.S. imports thousands of metric tons each year from countries where circulating foreign animal diseases have been identified."
Given ASF is the most significant foreign animal disease threat to U.S. swine production, Niederwerder said the primary goal of negative countries, such as the U.S., is to prevent ASF entry as there are no vaccines or treatments available.
"The recent introduction of ASF into historically negative countries over the last few years has heightened the risk for further spread," Niederwerder said. "Investigations in my laboratory have characterized the stability of the African swine fever virus in feed ingredients subjected to transoceanic shipment conditions, the virus's transmissibility through the natural consumption of plant-based feed, and the mitigation potential of certain feed additives to inactivate African swine fever virus in feed."
One investigation, conducted by Scott Dee et al. (2018), evaluated risk by using a transboundary shipment model and 12 feeds, ingredients, or products of animal origin based on import volume and use in swine feed ingredients. Ingredients included conventional soybean meal, organic soybean meal, soy oilcake, DDGS, lysine, choline, vitamin D, moist cat food, moist dog food, dry dog food, pork sausage casings, and complete feed.
Following inoculation with ASFV Georgia 2007, the ingredients were exposed to fluctuating temperatures and humidity that replicated real-world meteorological conditions during transoceanic shipment. Ingredients were tested for the virus at the conclusion of the simulated shipment model. After 30 days of transatlantic shipment conditions, researchers found that ASFV Georgia 2007 was broadly stable across diverse ingredients, with infectious virus being detected in 75% (9/12) of the tested ingredients, including conventional soybean meal, organic soybean meal, soy oilcake, choline, moist cat food, moist dog food, dry dog food, pork sausage casings, and complete feed.
“Importantly, several of the ingredients identified as supportive to ASFV also provided an environmental matrix that stabilized other diverse viruses of concern to swine health,” Niederwerder noted.
Niederwerder's latest review describes the current knowledge of feed as a risk for swine viruses and the opportunities for mitigating the risk to protect U.S. pork production and the global swine population from ASF and other foreign animal diseases.
"Epidemiological evidence has linked contaminated feed with African swine fever virus field outbreaks in both Europe and Asia," Niederwerder said. "A rapidly expanding geographic distribution of African swine fever virus continues to increase the risk of U.S. incursion. With economic losses of African swine fever virus introduction into the U.S. swine herd estimated at more than $15 billion due to production losses and market disruption, the importance of preventing entry cannot be overstated."
Niederwerder's article looks at potential ways to reduce ASF risk through feed biosecurity as well as through both physical and chemical mitigation protocols, such as heat treatment, storage time, and antimicrobial feed additives.
According to the report, assessment of risk starts with characterizing the necessity, source, and virus stability data of each feed ingredient. Additionally, Niederwerder emphasized that feed, ingredient, and feed mill biosecurity is essential for reducing infectious disease risks at all stages of swine production, and implementation of biosecurity procedures focused on feed can help address these risks.
"It is critically important that feed mitigation strategies continue to be investigated and adopted to reduce the risk of ASFV or other foreign animal disease entry through this route," she said.