Composting
A promising disposal method for ASFV-infected swine
By Lindsay Gabbert and Margarita Yatsevich
African swine fever continues to dominate discussions within the swine industry, with biosecurity at the forefront of every producer’s mind. As seen globally, ASF outbreaks among domestic pigs result in high numbers of swine mortality attributed either to infection with the disease itself or culling to contain the spread.
An important consideration when developing localized outbreak response and recovery plans is to identify practical and biosecure carcass disposal options that minimize potential transmission of disease to healthy swine populations.
Scientists at the Department of Homeland Security Science and Technology Directorate’s Plum Island Animal Disease Center demonstrated the effectiveness of composting as a disposal method for ASFV-infected pig carcasses in a recently published a paper in the journal Transboundary and Emerging Diseases.
Current carcass disposal methods for swine, such as incineration, landfill and deep burial, may increase the probability of spreading disease as infected animals are typically transported off-farm to secondary disposal sites where maintaining biosecurity can be challenging.
One benefit of composting is that it can be done in situ on many farms, thus minimizing animal movement and reducing overall biosecurity risks.
Despite that composting is a well-known technique regularly employed for disposal of routine animal mortalities, scientific data evaluating the kinetics of the ASF virus (ASFV) inactivation in infected pigs during composting was lacking.
S&T scientists at PIADC studied the ability of ASFV to remain infectious in swine tissues composted over 37 days using four ASFV-infected pigs.
The swine carcasses were composted within a static, nonaerated windrow comprised of layers of common carbon materials including wood chips, horse manure and pine shavings inside the PIADC Biosafety Level 3-Ag containment facility.
By the fifth day, the windrow reached the minimum target temperature of 55°C (131°F), and elevated temperatures were maintained at or above this threshold for 18 days.
Actively composting spleen tissues, with high starting concentrations of ASFV, were collected from each pig at designated timepoints throughout the study and analyzed for the presence of infectious ASFV by virus isolation in tissue culture. Results demonstrated that infectious ASFV was undetectable in the spleen by day five.
After 37 days, the scientists disassembled the compost pile and collected any remaining tissues (e.g., bone marrow, muscle) for additional testing. Again, none of the tissues sampled were found to contain infectious ASFV, however, viral DNA was still detectable in all samples by molecular methods.
The research results provide evidence that ASFV can be inactivated in ASF-infected swine carcasses at the early stages of composting—information that may be used to inform emergency response and carcass disposal policies for future disease outbreaks in swine.
To protect U.S. livestock, DHS S&T prioritizes applied agricultural biosecurity research. As long as ASF remains a threat to swine producers, S&T will continue to develop, test and evaluate countermeasures to prevent the introduction and spread of this animal disease, and mitigate its effects should an outbreak occur within U.S. borders.
Cover photo: S&T researchers Lindsay Gabbert (foreground) and Jose Barrera collect samples from the compost pile. Photo: PIADC.
Gabbert is a microbiologist and lead researcher of the study at the DHS Science and Technology Directorate’s Plum Island Animal Disease Center, and Yatsevich is a science writer/editor for DHS S&T.
