African Swine Fever: Biosecurity Coordination and Early Detection to Mitigate the Risk

By Stevie Kiesel, Biodefense PhD Student

The 6th International Biosafety and Biocontainment Symposium, presented by the US Department of Agriculture’s Agricultural Research Service (USDA ARS), brought together experts from government, academia, and industry to discuss emerging biorisk challenges in agriculture. Speakers highlighted how the convergence of food, agricultural, and natural resource challenges require coordination and intensification of food safety, nutrition, and food security efforts to mitigate risks.

I attended this virtual conference along with my GMU Biodefense Program colleagues Ms. Rachel-Paige Casey and Ms. Michelle Grundahl. You can find their discussions of other symposium sessions here. This report provides an overview and commentary on Session I, which dealt with the biosecurity risks associated with African Swine Fever virus (ASFV). Speakers for this session were as follows:

  • Dr. Douglas Gladue, US Department of Agriculture, “African Swine Fever”
  • Dr. Vittorio Guberti, Institute for Environmental Protection and Research, “Feral Pig Population”
  • Dr. David Pyburn, National Pork Board, “Prevention and Preparation for ASF”
  • Dr. Jishu Shi, Kansas State University, “International Perspectives: Past, Present, and Future”
  • Dr. Jack Shere, US Department of Agriculture, “ASF: The US Perspective”
  • Dr. Cassie Jones, Kansas State University, “Biorisks on the Farm: Practices to Prevent Pathogen Transmission to and from Animals”
  • Lindsay Gabbert, Plum Island Animal Disease Center, “Disinfection/Decontamination for Various Surfaces Effective Against ASFV”

In the midst of the COVID-19 pandemic, much attention is on zoonotic diseases—infectious diseases caused by a pathogen that has jumped directly from an animal to a human. While zoonotic diseases clearly represent a significant risk, other diseases that do not directly infect humans can still have a substantial impact. For example, though the ASFV is not transmitted from pigs to humans, the virus’s spread has inflicted serious economic pain in multiple outbreaks. However, these consequences can be largely mitigated through prevention and early detection efforts. This report summarizes the speakers’ key takeaways and suggests areas for future research and policy development.  

ASF is a highly contagious, highly lethal disease that is rapidly transmitted among wild boar, warthogs, and domestic pigs. Though the virus cannot be transmitted to humans and does not pose a food safety issue, ASF outbreaks have the potential for devastating economic consequences. For example, as Dr. Shi points out, China lost tens of millions of pigs in the first few months of their most recent outbreak, and the social and economic impact was severe. Dr. Pyburn estimates that an ASF outbreak in the US that took 10 years to control could cause $50 billion dollars in losses and 140,000 job losses. Even in a rosier scenario where the US controlled the outbreak after 2 years, projected losses are $15 billion.

ASF is endemic in Africa, particularly in sub-Saharan Africa. Its natural hosts there are warthogs and bushpigs, with soft ticks acting as a vector. In the 1950s, outbreaks began occurring in Europe, and later in the Caribbean, likely via contaminated pork products. European countries combatted ASF with a policy of slaughtering infected animals and modernizing farming facilities, and by the 1990s Europe was declared free of ASF. However, in 2007, ASF was identified in the country of Georgia, presumably attributed to the importation of contaminated pork. This outbreak spread quickly to neighboring countries among their wild boar populations, to such an extent that ASF was declared endemic in the Russian Federation. Despite enacting slaughter policies and other measures, ASF has not been eradicated from eastern Europe. Another key event is the 2018 introduction of ASF in China. This outbreak spread rapidly across Asia, with significant economic impacts. For example, China saw a 50% reduction in its swine herd in 2019. ASF has also spread to other European countries, such as Belgium, Poland, and German, in recent years. The World Organization for Animal Health (OIE) found that as of December 2020, there are ongoing ASF outbreaks in 24 countries: 8 in Europe, 12 in Asia, and 4 in Africa.

There are several key challenges in eradicating ASF. Both wild and domestic porcine animals can spread the virus. The main challenge in addressing an outbreak among wild boar is their uncontrollable movement and the need to quickly remove infected carcasses to stem the spread. In winter temperatures, a carcass can maintain the virus for months or years. Therefore, even though ASF initially spreads in a wave with a high fatality rate (~60%), the infected carcasses as a source of infection can cause ASF cases to persist locally for years. European countries have pursued three different strategies to manage infected wild boar populations: depopulation (90% of the total wild boar population hunted), soft hunting (60% of the post-reproductive population hunted), and fencing of infected populations coupled with a hunting ban. Depopulation was the least successful, while soft hunting led to a slow but still steady spread of disease. However, banning wild boar hunting and erecting a double fence around identified infected populations has been successful in eradicating the virus in the Czech Republic and Belgium, though further research is needed to understand the conditions under which this strategy is and is not effective.

For domestic pigs, the main challenges to ASF eradication are an underreporting of symptomatic animals, the inability of smaller farms to implement adequate biosecurity measures, the contamination of feed, and illegal domestic pig movement. Dr. Jones argues that an often-overlooked weakness in the US is the feed supply chain as a potential pathogen transmission route, involving the ingredient facility, the feed mill, and individual farms. Obviously, contamination at the ingredient facility or feed mill can be spread to many farms, but more attention should be paid to delivery drivers transporting feed from the mill to farms and moving from farm to farm without adequate hygiene measures in between trips. A culture of biosecurity, as well as clear and appropriate information reporting measures, is key to mitigating the many points of entry for infectious diseases to spread rapidly on and from individual farms.

As the saying goes, “You can’t fatten the pig on market day.” To prevent a large-scale, economically devastating outbreak of African Swine Fever (ASF), stakeholders must coordinate on robust biosecurity, disease surveillance, and containment measures. Preparation is key; responding to an outbreak after it happens will lead to catastrophe. The symposium speakers had many promising ideas for future research to address current gaps. While the USDA has developed experimental live attenuated ASFV vaccines, more research is needed on protective immune mechanisms; subunit vaccines could also be explored. More development of computational models to understand the spread of ASFV, particularly in wild boars, would be a helpful tool in tracking and eradicating the virus. Focused study of eradication methods and their implications on economies and the environment would point to tailored strategies for an outbreak of a wild or domestic origin. Speakers also discussed ongoing projects to address ASFV, such as an educational initiative with Customs and Border Protection to increase biosecurity awareness as it related to passengers entering the US from foreign ports. The National Pork Board is also developing a tool called AgView, a data dashboard that provides real-time ASFV updates and pig movement data to state health officials, increasing collaboration and information sharing. The combination of industry, government, and academic stakeholders at this symposium reflected the broad portfolio of efforts currently underway to address ASFV.

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