Though it isn't present yet in the United States, African swine fever's global spread since 2007 poses a serious threat to the U.S. swine industry. This deadly swine virus can cause extremely high mortality, and no treatment or widely approved vaccine are available to protect pigs from it. Because of its severity, ASF-infected herds are depopulated to prevent the disease from spreading.

Previous reports have estimated that due to control measures and lost markets, an ASF epidemic could cost the United States about $50 billion across 10 years. It is vital that the U.S. swine industry be prepared against this massive threat.  

Surveillance, the activity of looking for diseases in populations, is a powerful tool in the fight against ASF. Passive surveillance refers to disease monitoring by farmers and their veterinarians, such as reporting suspicious clinical signs to a veterinary official. Consistent and comprehensive passive surveillance is vitally important to detect an outbreak as quickly as possible, which could make the difference between swiftly stamping out ASF or a prolonged, costly struggle.

However, early detection of ASF is difficult. ASF-infected pigs can look like many other diseases, such as porcine reproductive and respiratory syndrome. High herd mortalities may eventually raise suspicion of ASF, but because the virus spreads slowly, this may occur too late to prevent wide-scale outbreaks and losses. Additionally, labor and economic constraints can make consistent on-farm surveillance difficult to implement.

To address these concerns, researchers at the University of Minnesota Center for Animal Health and Food Safety are exploring novel ways to help swine producers identify a potential ASF-infected pig on their farms as early as possible.

Passive surveillance can be enhanced through standardized tools such as computer algorithms, scorecards and specialized training, all of which can improve the U.S. swine industry's capacity for early ASF detection. With funding from the USDA, the CAHFS team developed an "enhanced passive surveillance" (EPS) protocol for ASF.

The tool is based on three components: 1) an initial farm biosecurity self-assessment, and weekly recording of 2) clinical signs from live pigs and 3) necropsy findings. Each factor in the protocol was assigned a score by global ASF experts, and when present, those factors increase the weekly score. High scores could be indicators of an ASF introduction.

To test the EPS protocol in the field, the CAHFS team piloted it in the Dominican Republic for 10 weeks. Each week, depending on their initial biosecurity assessment and what clinical signs and necropsy findings they reported, the farms were assigned a score. Significantly high scores were detected twice during the trial period, and though ASF was not detected, the system demonstrated how EPS can act as a consistent, standardized on-farm protocol that improves clinical monitoring of pigs and early disease detection.

The CAHFS researchers are now studying how the EPS protocol could be adapted for U.S. swine farms and take advantage of ongoing disease surveillance practices. Through a survey of Minnesota swine farms and a workshop with public and private swine stakeholders at the 2022 Leman Conference, participants identified many opportunities to improve on-farm recording and monitoring of clinical signs and necropsy findings. They highlighted that for more consistent surveillance, clinical observations needed to be collected in a simple, standardized way, such as scorecards.

They felt that EPS could be valuable for identifying concerning disease trends on farms, such as a PRRS outbreak, and to help in training farm workers with how to identify important early clinical signs of swine diseases. Important considerations such as labor requirements and diagnostic testing costs were also highlighted. Using this feedback, the CAHFS team plans to keep developing novel ways to help swine producers conduct efficient and effective disease surveillance, from adapting the EPS protocol to U.S. farms, exploring the use of point-of-care tests and precision livestock technologies, and more.

For devasting diseases like ASF, even hours to days of earlier detection can make a significant difference to protect the U.S. swine industry and maintain our pork trade. With the continued support of public and private partners, the team at CAHFS hopes to keep helping swine producers with novel and useful ways to conduct disease surveillance and protect their herds from ASF.         

For more information on this topic, please see our open-source articles in Frontiers in Veterinary Science and the WOAH Journal.

If you want to learn more about EPS, contribute ideas, or explore a collaboration on improving swine disease surveillance, please contact CAHFS researcher and veterinarian, Rachel Schambow via email. Schambow and the CAHFS team will gladly provide advice free of charge to veterinarians and producers interested in enhancing their ability to early detect ASF and other foreign diseases of swine.