Emerging swine diseases: where is diagnostic surveillance headed?
The evolution of swine disease surveillance and what comes next
12 December 2022
4 minute read
By: Dr. Jeff Zimmerman, with the Iowa State University Veterinary Diagnostic Lab, speaks to The Pig Site’s Sarah Mikesell at the North American PRRS Symposium in Chicago in early December.
Evolution of swine surveillance
“Diagnostic surveillance is a great topic and is very timely because, as we're looking forward to try to control or prevent African swine fever, we have to tailor our surveillance to the industry and the purpose for which we're using it,” said Dr. Zimmerman.
Swine disease surveillance has changed over time. Remembering the hog cholera (classical swine fever) eradication program in the US, which was successfully completed in 1978, the surveillance method used then was to test every pig in the herd. This was more manageable in the 1970s because herds were relatively small, averaging about 50 pigs.
“When we came to the pseudorabies eradication program in the early 1980s, the discussion came up, ‘do we continue sampling every pig in the herd or do we use a new technique?’” he said. “Thankfully, they chose to use a new technique, which was representative sampling. So, instead of sampling every pig in the herd, they took a sub-sample, and most of us know that a sub-sample was usually 30 pigs. Thus, if you went into a barn of 1,100 or 1,200 pigs, you'd sample 30, not 1,200.”
Presently, surveillance has continued to evolve. Pig populations are typically much larger and are much more complex. Now the focus is on preventive surveillance for diseases like African swine fever and classical swine fever.
“We need to change again - one of the things we've seen recently is different sample types. In classical swine fever, hog cholera, or pseudorabies, it was only serum samples,” he explained. “Today, we need to use other kinds of samples, and that can be processing fluids like oral fluids, tongue tips, or any variety of aggregate samples that we're developing.”
The other change to ensure affordable yet effective surveillance is reconsidering how many samples we collect. In the pseudorabies eradication program, every herd got tested at some interval - usually once a year and sometimes more often. In the case of an African swine fever or classical swine fever outbreak, producers would work in coordination with their veterinarians to collect a limited number of targeted samples - perhaps 10 samples.
“What we've seen over time is that and as the Europeans are recommending, if you target the pigs that are doing poorly, it increases the probability that you'll actually find a positive sample. We reduced the number of samples per herd, but we're asking for more participation,” he said. “In other words, we'd have a surveillance program set up where most herds would test at about the same period of time. That gives you a very sensitive, very detailed picture of what's going on in the system. It turns out that if producers collect those 10 samples and pool them into samples for testing, the cost on a regional basis is about one cent per pig in inventory, making it pretty cost effective. It's also relatively easy because we're using samples that are easy to collect – it could be oral fluids, it could be oral swabs, other simple to collect samples, but the overall sensitivity of the system is magnificent."
This is the kind of approach that the Swine Health Improvement Plan (US SHIP) may recommend for our ongoing African swine fever and classical swine fever surveillance. The US SHIP program has a committee made up of producers, veterinarians and state and federal government officials, and the committee will determine the surveillance program and testing that will be put into place.
What action should US pig producers take?
US SHIP is modeled after the National Poultry Improvement Plan, which has been around since 1935. Stakeholders come together to decide how to best control disease and improve the health of the industry. Producers are encouraged to sign up with SHIP and become involved.
“We need these parts in place, even if we're not conducting active surveillance. If the parts are in place, we can quickly implement the program and find out exactly where African swine fever or classical swine fever is at so we can take decisive and effective action,” he concluded.
