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First-hand ASF experience offers lessons for US industry

27 July 2021, at 9:00am

Plan for the worst; hope for the best. That’s good advice for many situations but particularly accurate when it comes to African swine fever (ASF). So far, the US has kept the virus from reaching its swine herd, but that doesn’t mean producers, caregivers or swine veterinarians can temper their vigilance.

In fact, remaining vigilant is a key message that Keith Erlandson, DVM, Zoetis, wants to drive home to the US swine industry. “We need to keep reminding people that ASF is still out there, and it could get into the US,” he told Pig Health Today.

Erlandson spent 5 years in China working with a range of integrated production sites and was involved with a sow farm that broke with ASF 1 month after the Aug. 3, 2018, index case. Within a month, the virus had spread to five other provinces, and by year’s end ASF had infected the entire country. Over the course of nearly 3 years, he gained first-hand experience dealing with the disease from sow farms to finishing sites. Among the lessons learned was that the course of the disease, diagnosing cases, as well as control and eradication are all more complex than anticipated.

Not in the book

While you may have reviewed the clinical signs of ASF in recent years, the virus hasn’t. “I had believed that an ASF infection would be apparent as soon as I walked into the barn and saw tell-tale clinical signs listed in any edition of Diseases of Swine,” Erlandson said.

Instead, ASF shares common signs with other swine diseases, at least in the critical early days. Most pronounced were sows off feed and some vomiting, which could suggest a number of diseases, including porcine reproductive and respiratory syndrome (PRRS), porcine epidemic diarrhea virus and even swine influenza virus.

In the case of ASF, sow or finishing-pig mortality will start to tick up but may be viewed as day-to-day variations. Erlandson relayed that one sow may die today, then none, with three or four dead a few days later. “It takes a couple of weeks for ASF to ramp up to where it’s glaringly obvious and triggers a reaction,” he pointed out. “I was expecting the disease would move very quickly through the farm, but it takes longer than I expected.”

That detail offers the opportunity to gain control over the virus by acting quickly, within a day or two. But it also allows the virus to continue to move undetected.

A watchful eye

It’s worth noting that the farms Erlandson worked with in China were completely closed, yet they could not identify the source of infection. “The farm was in a high-risk area, but whether it was rodents, insects, windborne, I don’t know,” he said “There has to be some area spread.”

Once infected, the farms quickly adopted these protocols:

  1. Every morning the number of sows off feed were reported and those animals were tested for ASF. China developed a pen-side PCR test, which is something the US does not have but would be vital to control efforts.
  2. All sow and pig mortalities were necropsied and sampled.

The necropsies, while helpful, also can lead to confusion early in the infection. “Gross lesions are frequently seen, but animals may not exhibit them all, and those lesions are associated with other diseases,” Erlandson noted. For example, enlarged spleens were found in 80% of cases but not 100%, and there was great variation in size. Hemorrhagic kidneys and lymph nodes were common, but hemorrhagic skin lesions were not a consistent finding.

In addition to sampling dead sows and pigs, environmental samples were collected to identify contaminated areas requiring attention.

An extensive test-and-remove strategy to address ASF-positive sows and pigs, as well as neighboring exposed animals, allowed the farm to successfully stop the infection within its system. In the end, approximately 400 sows were culled from farrowing and gestation, as were any associated piglets. Whole-herd testing protocols were repeated every 2 weeks until all tests came back negative.

The production site already had an intensive truck-use system in place, with trucks designated to move only weaned pigs and other trucks dedicated to slaughter and cull animals. An animal transfer station ensured that the slaughter/cull trucks would not come within 2 kilometers of a sow or wean-to-finish farm. A tiered truck-wash system required all trucks to be washed, disinfected and dried (thermo-assisted) twice between use. Feed trucks from the mill also would be washed, disinfected and dried twice before reaching the farm where they would auger feed into trucks dedicated to the site.

Supplies followed a similar wash, disinfect and UV chamber-exposure protocol, which was repeated three times before supplies entered the barn for use. This process could take 10 to 14 days from delivery, Erlandson noted.

Advice for US farms

US producers may not embrace such an extensive truck-use and disinfection program, but Erlandson said transportation biosecurity will require greater commitment. “Trucks are our biggest vulnerability, specifically those returning from slaughter plants,” he said. “If ASF does get into the country, systems are going to have to prepare for a new era of biosecurity.”

And it will require a significant investment in biosecurity infrastructure. This means more dedicated trucks for specific production phases — moving only weaned pigs and only market hogs/cull sows — with designated truck washes that also include disinfection and thermo-assisted drying. It also will require more labor and time.

Caregivers are the first line of defense as they will be the first to spot any signs of ASF. Make sure they are trained on the clinical signs of ASF, including the gross lesions, but that they also consider “unusual” developments. For example, high mortality rates are associated with PRRS, but that doesn’t mean mortalities are always due to that virus. “It’s important that we all take mortalities seriously,” Erlandson said. “We may not be investigating mortalities as closely as we should be.”

Don’t hesitate to test and investigate further — even now. “If ASF comes here, we’re going to have to do a lot more testing,” he added. In China, every time a farm called to report sows off feed, the veterinarians would be on the edge of their seats until ASF-negative results came back, he relayed. “I never thought I’d say this, but I’ve gotten results back and was relieved to find out it was only PRRS.”

Evaluating the system’s biosecurity top to bottom is something to do now, but biosecurity protocols will be even more critical should ASF arrive in the US. Train, monitor and keep workers updated on biosecurity measures.

“My experience has led me to believe that to combat ASF, producers and veterinarians must hold two mutually exclusive facts at the same time,” Erlandson said. “That ASF is a disease that’s difficult to transmit and that ASF is easy to transmit. We must be able to select which statement applies to solve the problem at hand, with the knowledge that the next case may require us to think of the disease in completely contradictory terms.”