Responding to outbreaks of transboundary animal diseases is just one of the many challenges emergency planners and responders in rural localities face. Unfortunately, the infrequent nature of these events makes it easy to put off the planning, training, and research needed to fully prepare for animal disease outbreaks.
The highly pathogenic avian influenza (HPAI) outbreak of 2015 is a reminder of the impact that animal disease outbreaks can have on local economies and resources. This outbreak impacted 211 commercial poultry farms and 21 backyard flocks from California to Indiana and tasked responders with the disposal of 50 million birds carcasses. Disposing of so many carcasses without further spreading the disease or causing significant environmental harm was no easy task.
In August 2018, another animal disease caught the attention of agricultural first responders when African Swine Fever (ASF) was detected in the northeastern Chinese province of Liaoning. It quickly spread across the country. Since then, ASF has moved rapidly throughout Asia and Europe. Fortunately, ASF is not a zoonotic disease and, therefore, does not cause sickness in humans. However, it devastates economies and destroys the livelihoods of small farmers.
During the disease outbreak, researchers and emergency planners began working to improve the level of preparedness for a potential outbreak within the United States. Among the areas of focus was carcass disposal. Despite the animal carcass management experience that agricultural first responders had from the HPAI outbreak of 2015, not all of the lessons learned from the disposal of 5-pound laying hens transferred well to the disposal of 450-pound sows.
The need for an effective ASF response strategy is not just about avoiding disease transmission and environmental impacts. An outbreak of ASF in the United States would have catastrophic economic implications. A new study conducted by agricultural economists from Iowa State University and the Universidad de la Republica in Uruguay estimates that an ASF outbreak in the United States could have an economic impact of $50 billion.
Wake Up Call
In July 2021, the Dominican Republic reported to the World Organisation for Animal Health (OIE) that they had a confirmed case of ASF. This was the first reported case of ASF in the Western Hemisphere in almost 40 years. Although the Ministry of Agriculture made aggressive attempts to control the outbreak, the disease quickly spread throughout the country and into neighboring Haiti. With only 60 miles separating the Dominican Republic and Puerto Rico, efforts to prepare for and prevent an outbreak within the United States intensified with an urgency not seen since the 2015 HPAI outbreak.
Mortality Management Research
Composting has become a preferred method to manage poultry carcasses during disease outbreaks and natural disasters. In fact, 85% of the 50 million birds impacted by the 2015 HPAI outbreak were composted, and the generated compost was beneficially used as a soil amendment (see Figure 1). Because of that success, it is natural to assume that emergency responders would look to composting to manage disease outbreaks and natural disasters impacting livestock.
Unfortunately, the size of each animal and the sheer volume of carcasses on a typical livestock operation add complexity to the composting process. While poultry can be composted in 28 days, livestock can take 3 to 6 months to compost. Additionally, composting livestock requires a considerable amount of carbon material, such as woodchips or corn stover. To address these challenges, researchers initiated a number of projects to make the composting process more efficient for pigs and other livestock.
Grinding and Composting
In 2018, researchers conducted a proof-of-concept project in Virginia to evaluate the effectiveness of grinding swine carcasses with a horizontal bed grinder before composting. Based on the results of this project, the team conducted a series of operational scale research and demonstration projects in North Carolina and Minnesota (see Figure 2). These projects evaluated the methodology’s throughput, the carbon material requirements, the potential for pathogen aerosolization, and the impact on the composting process. These evaluations suggest that grinding carcasses prior to composting can significantly reduce composting times, making the procedure similar to the process used during the 2015 HPAI outbreak in poultry.
An ongoing area of research is the evaluation of air emissions from the grinding process. With the use of air monitoring stations around grinding sites, researchers from the United States Environmental Protection Agency’s Office of Research and Development are working to determine if it is possible for the grinding process to spread dust particles containing the ASF virus (see Figure 3). They are also evaluating mitigations such as the use of shrouds and misters to minimize dust emissions from the grinding process.
ASF Inactivation Through Composting
Although composting has been shown to inactivate a variety of pathogens, studies had not been conducted to confirm its effectiveness for inactivating the ASF virus. To address this uncertainty, a team of U.S. and Vietnamese researchers, with funding from the National Pork Board, conducted a research project on the campus of the Vietnam National University of Agriculture in Hanoi, Vietnam. In the study, pigs from local farms presenting typical ASF symptoms were collected and confirmed to be positive for ASF by laboratory testing. Each of the pigs was placed in compost piles from which tissue samples were collected to test for viable virus particles. Compost pile temperatures were monitored daily. Although data analysis has not been finalized, initial results suggest that composting can quickly and effectively inactivate the ASF virus in swine carcasses.
Above Ground Burial
In 2015, researchers in Virginia began evaluating the effectiveness of Above Ground Burial (AGB) as a carcass disposal method. AGB is a hybrid of traditional deep burial and composting, designed to increase carcass decomposition and minimize environmental impacts. Since then, AGB research projects have been conducted in Virginia, North Carolina, Texas, Oklahoma, and Minnesota, looking at carcass decomposition, scavenger activity, nutrient migration, insect activity, and pathogen inactivation (see Figure 4).
Based on this work, AGB appears to be a viable carcass disposal option during large livestock mortality events. When conducted following USDA’s standard operating procedures, AGB minimizes the vertical migration of contaminants, prevents scavenger activity, and enhances carcass decomposition.
AGB has also been shown to inactivate a variety of pathogens, including the swine pox virus and Seneca Valley virus. Because the U.S. is currently ASF-free, it is difficult to conduct research on the virus domestically. However, research to confirm that AGB will inactivate the ASF virus has begun on the campus of the Vietnam National University of Agriculture in Hanoi. Results from this project will inform the future use of AGB during ASF outbreaks.
Use of AGB During an Agricultural Emergency
The AGB disposal method has mainly been implemented at a small-scale during research projects. It was first used as a disease management tool in Tunisia to dispose of sheep testing positive for the Foot and Mouth Disease (FMD) virus, Peste des Petits Ruminants Virus (PPRV), and Bluetongue Virus.
Its first use in the U.S. as an emergency mortality management tool was in May 2021 in response to a barn fire at a 5,000-head sow farm in Minnesota. Tragically, the fire resulted in the deaths of 3,000 sows and 8,000 piglets. Traditional deep burial was not an option due to the shallow groundwater table common in Minnesota and many other places across the U.S. The farmer considered landfilling the carcasses, but ruled it out due to costs and instead chose to implement AGB.
Training First Responders
Animal mortality management can be a complex process. Effectively implementing disposal methods such as composting and AGB is both an art and a science. Mortality management subject matter experts (SMEs) who oversee the carcass disposal process typically have a combination of classroom and field training. To build regional capacity in the event of an outbreak of animal disease such as ASF, the United States Department of Agriculture, Animal & Plant Health Inspection Service (USDA, APHIS) sponsored a series of mortality management training programs focused on creating new mortality management SMEs. These training courses teach the skills necessary to implement both composting and AGB. The courses have been held in Maine, North Carolina, and Iowa, with additional courses scheduled for Oklahoma and California.
Where to Go From Here
The U.S. has made significant strides in increasing its readiness for the possibility of an ASF outbreak. Although much research has been completed, there is still more to learn about how to effectively control outbreaks of this devastating disease.
In addition, additional mortality management SMEs need to be trained to ensure rapid control of the disease and prevention of environmental contamination from decomposing animal carcasses. There are already several training opportunities planned. A half-day mortality management workshop is being held as part of the U.S. Composting Council’s COMPOST2022 conference scheduled for 24-27 January 2022 in Austin, Texas. Another learning opportunity is the 7th International Symposium on Animal Mortality Management to be held 27-30 June 2022 in Raleigh, North Carolina.
As infrequent as animal disease outbreaks may be, there must be continual investment in the training and research needed to ensure an effective and efficient response.
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