Source: Swine Health Information Center (SHIC)
Since African swine fever (ASF) was diagnosed in China in August 2018, veterinarians have been studying the virus’s characteristics and learning how to manage in barns. The Swine Health Information Center (SHIC) is monitoring these processes as part of its mission of preparedness for foreign animal disease management for the US national herd. Two US-based practitioners have experience with ASF management practices in China and shared their perspectives with SHIC.
Joe Connor, DVM, founder of Carthage Vet Service, believes knowing about transmission of the virus has helped practitioners in China institute a test-and-removal strategy for effectively managing ASF spread. Keith Erlandson, DVM, works in pork production in China and shares their strategy for test-and-removal. Both cite the slow spread of ASF as the key factor enabling successful test-and-remove protocols.
This successful experience in China contains great value for American swine practitioners. “This is teaching us we need to move to the next step of biosecurity, which is biocontainment, which can apply to other viruses and bacteria we see,” Connor said. “It’s a matter of changing mindset. What can we do in the next generation biosecurity which is biocontainment? Think in terms of individual population effect on larger adjacent populations.”
Using the USDA grant received last fall to open ASF dialogue and research in Asia, SHIC is beginning projects focused on test-and-remove protocols during work conducted in Vietnam, with the intent to measure efficacy and provide guidance for similar biocontainment practices for domestic herds. The experience in China is also informative to the process.
“The idea is to stop transmission because the virus moves relatively slowly,” Connor said. “So what we see has developed in China is, through experience, better detection of early clinical signs of an animal that is infected. Second would be readily available PCR diagnostics so they can very quickly confirm a yes or a no. Third, they lockdown that gestation area (with infected animal(s)) by individual stall or stalls if there’s a solid pen divide between groups, or if there are no solid dividers between the stalls, the lockdown is by the trough. If the suspect or positive animal is in finishing, they lock down the individual pen with the animal and the pens on each side.
In both situations, they lock down the barn until further testing can be done and decisions made. When they have a suspect animal or animals and are waiting for confirmation, they totally lock that building down for people movement, traffic in and out, and animals in and out, until they get confirmation of a yes or a no. Fourth, they take great care in removing those positive animals to prevent transmission. They have learned to focus on containment to stop the spread,” Connor said.
Erlandson has been directly involved with successful test-and-removal management of ASF.
“When ASF initially broke, we were of the mindset that we needed to eradicate it. Anytime ASF broke on a farm, we would euthanize the whole population, clean and disinfect the premises, and start over,” he said. “When it became clear ASF was going to become endemic, depopulation just because we had a positive test was not an economically viable solution. Due to the economics, we, among others, started working on test-and-removal. What we found is the virus does not spread as quickly as we were originally led to believe, especially in a sow herd where animals are individually housed.”
Connor and Erlandson agree the first step for successful test-and-remove protocols is recognizing the clinical signs of ASF in pigs. This requires frequent and repeated education for direct-care workers.
“I thought if you walked onto a farm with ASF you would know it instantly, but that’s not what happens. Initially, there may be only one or two animals infected, the mortality of one or two animals may not even be noticed. The disease often doesn’t raise alarms early on, so there is the chance of missing early cases if you are not vigilant,” Erlandson said.
Erlandson said sows being off feed is an automatic trigger for ASF testing in barns under his care in China. Testing is done by oral swab. He said this testing process is relatively easy for all staff to do as compared to collecting blood or serum. However, positive oral swab results leads to whole blood or serum PCR tests.
“I think one of the big reasons finisher farms get infected is by contamination from the truck taking animals to slaughter,” Erlandson observed. “Of the finishing cases I’ve seen, I believe 70% to 80% of the breaks are due to transportation to the slaughterhouse. When a site with market age pigs breaks, you euthanize any animal with clinical signs and get everything else on the truck to market as soon as possible.”
What follows is cleaning and disinfecting of the barn before new animals arrive. For younger animals, Erlandson says they are assessed and whole pens where clinical cases are found will be euthanized as well as pens on either side as appropriate. Testing occurs frequently and close monitoring for clinical signs continues.
Using test-and-removal protocols based on farm design has been successful for Erlandson’s company.
“Depending on the situation and how quickly ASF is recognized, I have seen a success rate of 70% to 80%,” he reported. “After a test and remove, generally we want three weeks of clean testing and cleaning and disinfecting of the farm, after which the farm can open back up.”
To learn more about the global status of ASF, watch swine veterinarians Liz Wagstrom of the National Pork Producers Council, Gordon Spronk of Pipestone Veterinary Services and Patrick Webb of the National Pork Board in the Farm Journal PORK Week webinar.
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