If African swine fever strikes the United States, some farmers will suddenly need to dispose of a lot of dead pigs.
And they’ll have to do so in a way that prevents the disease from lingering in the environment.
Composting the carcasses might be the answer, researchers said May 18 during the Virtual International Symposium on Animal Mortality Management. The event was hosted by North Carolina State University.
Composting uses microbes and the heat they generate to break down all kinds of organic matter, from old produce and manure to weed seeds and some pathogens. Many dead chickens were composted in huge piles during the 2015 avian influenza outbreak in the Midwest.
Since then, African swine fever has produced animal carnage across a much broader territory — from Eastern Europe to Southeast Asia. Experts predict a U.S. outbreak could cost the swine industry billions of dollars.
As a result, USDA and other federal agencies have formed a task force to speed up the development of a vaccine, improve diagnosis and surveillance, and — this is where compost comes in — find the best ways to clean up after an outbreak.
The virus that causes African swine fever is a bit of a challenge to kill. It can survive for a long time in dead animal tissue and is stable over a wide pH range, said Lindsay Gabbert, a research microbiologist with the U.S. Department of Homeland Security who is part of the composting project.
Few U.S. labs are authorized to study African swine fever directly, and field studies are off limits.
So to attempt composting of contaminated pigs, Gabbert’s group at Plum Island Animal Disease Center built their compost pile inside a high-containment laboratory.
Plum Island, which sits on a nub of land at the edge of Long Island Sound, is the primary federal installation for researching foreign animal diseases.
Still, making compost indoors raised a lot of questions, such as whether insects would scamper out of the pile into the secure room, and whether the hot compost would pose a fire hazard.
“We’re not composting experts. We’re virologists and microbiologists, so that was something kind of new to us,” Gabbert said.
Having satisfied their initial concerns, the team sought out an essential ingredient for good composting — a carbon feedstock.
They obtained municipal wood chips, local horse manure and bedding — as well as baled pine shavings from Tractor Supply Co.
The group built the windrow indoors around four 120-pound pig carcasses that were infected with African swine fever and left over from a USDA vaccine study.
The researchers cut up the pigs’ spleens — large organs with high concentrations of the virus — and placed them in sampling bags that were restored to the pigs’ abdomens.
The idea was to have pieces of the pigs to sample while mimicking field conditions as much as possible, Gabbert said.
The scientists let the pile compost for 37 days before unearthing what was left of the pigs — mainly bones, ears, marrow and bits of muscle.
“We did end up with a pulled pork-like end product, which was quite interesting,” Gabbert said.
More important was what happened to the virus particles. By the fifth day, the team could not detect any live virus in the pig tissue.
Virus DNA was still present late in the study, though it had degraded considerably over time.
The study wasn’t long enough to determine if composting can completely destroy the viral DNA, Gabbert said.
An Option for Small Farms
While Gabbert is about planning for a potential swine fever outbreak, Duc Hoang Minh has been working on responding to an existing one.
African swine fever was first documented in Duc’s native Vietnam in February 2019. Since then, nearly 9,000 outbreaks have been recorded, reaching all of the country’s provinces, according to the World Organisation for Animal Health.
Burial has been the most common disposal method for large numbers of pigs. Burning has been used for very small groups and in places with high groundwater or risk of flooding, said Duc, a member of the veterinary faculty at Vietnam National University of Agriculture.
Unfortunately, many localities failed to collect and dispose of pigs from small farms, which have had most of the outbreaks due to poor biosecurity. As a result, some farmers have dumped their contaminated pig carcasses in rivers or by the side of the road.
“It seemed like the burial and the incineration was not convenient enough for farms, especially for the small farm, to dispose (of) their infected pigs by themselves,” Duc said.
He believes composting could be a reasonable do-it-yourself disposal option for these little operations. For one thing, Vietnam has plenty of rice hulls, rice straw and sawdust to use as the carbon feedstocks.
Duc composted several infected pigs outdoors for 144 days, by which time most of the pig tissue had decomposed.
He did not find the virus itself by day 3 in rice hull compost and day 7 for sawdust compost. Duc and his team found DNA from the virus in all samples for the first month, but they are continuing to crunch the numbers from the project.
So far, though, the results from both the U.S. and Vietnam suggest composting might make sense as a disposal method — though it would be far better to keep African swine fever out of America in the first place.