Learning From PEDv: Managing Disease In Manure And Mortalities

 

The economic impact of Porcine Epidemic Diarrhea Virus (PEDv 9078) on the U.S. swine industry is estimated at around $900 billion annually since it first began infecting herds in the spring of 2013. Research on persistence of the PED virus in manure and mortality compost piles conducted by Dr. Amy Schmidt and her colleagues in the USDA-ARS and the UNL School of Veterinary and Biomedical Sciences was presented during the November 4th Animal Care Wednesday Webinar by Nicole Schuster, a graduate research assistant in Dr. Schmidt’s lab at UNL. Dr. Schmidt’s research focuses on determining appropriate management strategies for composting PEDv-positive mortalities and inactivating the virus in stored manure from PEDv-positive pigs before applying it to the soil.

 

Why is this research important? Well, veterinarians have speculated that a thimble full of active PED virus from the manure or gastrointestinal tract of infected pigs could effectively infect all of the state of Iowa’s nearly 20 million pigs (1/3 of the U.S. pig population), so we need to be very aware of all of the potential vectors for the spread of this disease. Let’s look at what the research found and what we can apply to the other livestock species to maintain animal well-being and health.

 

 

Research funded by the National Pork Board has found that PEDv can be inactivated on metal surfaces (trucks and trailers) exposed to at least 150°F degrees for ten minutes or more. Additionally, burying mortalities is a concern because the virus thrives in cool, moist conditions so the virus could persist in the soil and lead to “re-breaking” of the disease (re-emergence of the disease on the farm) if the soil around the burial site is disturbed and the virus is reintroduced to naïve pigs on the farm. Taking this knowledge and knowing that effective composting practices can also achieve comparable temperatures, the inactivation of PEDv by composting mortalities was investigated. The researchers constructed three boxes for containing mortality compost piles in biosecure rooms on the UNL campus and utilized sensors to monitor temperature throughout the piles during composting. Carcasses positive for PEDv were placed in the constructed compost piles and allowed to compost. Two “cycles” of composting were conducted for each pile. The primary composting cycle of 36 days was followed by a secondary composting cycle lasting 40 days. Moisture and organic matter was added to the piles as needed to maintain appropriate composting conditions. After the first heating cycle, carcasses were about 60-80% degraded and the secondary cycle resulted in about 95% degradation of the carcasses. Samples of the compost material at the completion of each heating cycle, which did include some “un-degraded” tissue at the completion of the first composting cycle, tested negative for PEDv RNA showing effective inactivation. Temperatures in these small-scale compost bins reached about 130°F degrees during the first compost cycle. It is common for temperatures in larger piles to rise even higher, which should provide further confidence in the inactivation of the PED virus during the composting process. Dr. Schmidt would like to confirm results from this small-scale composting study by conducting on-farm mortality composting studies, but believes proper management of on-farm compost piles to achieve internal pile temperatures of at least 130°F degrees will be effective at destroying infectious virus from PEDv-positive mortalities.

 

 

Another research project investigated the survival of the PED virus in manure-amended soil with a complimentary study focusing on the effectiveness of adding lime to PEDv-positive manure to inactivate the virus. Because manure is commonly applied to land as a fertilizer following fall crop removal, Dr. Schmidt was interested in investigating how long the virus could survive in manure-amended soil over the winter to determine if the soil could be a vector for spreading the virus when spring field activities begin. In addition, she and her collaborators wanted to determine if adding lime to the manure prior to land application could eliminate infectious virus in the manure. For the liming study, quick lime was added to PEDv-positive manure to raise the manure pH to 10 for 1 or 12 hours. Limed manure and raw (untreated) PEDv-positive manure were used to inoculate piglets, which were then monitored for signs of PEDv infection. Piglets inoculated with lime-treated manure remained negative for PEDv, while piglets inoculated with the control manure samples (those not treated with lime) became infected with PEDv. From this study, Dr. Schmidt was able to conclude that treating manure with lime to raise the manure pH to 10 for at least 1 hour is an effective method for destroying infectious PED virus in the manure.

 

The study to determine virus survivability in manure-amended soil involved adding PEDv-positive manure or limed manure to soil in plastic tubes and incubating the samples over a period of 150 days at temperatures representing average soil temperatures in three climates – southern Minnesota, northern Missouri, and central Oklahoma – during the winter months. Incubation of these samples has been completed and analysis of samples for viral RNA is being conducted. A bioassay study where piglets will be inoculated with these soil samples will be conducted soon to confirm the viability of PEDv over time in soils exposed to these different winter climates. Dr. Schmidt expects the results of this study to answer the question of how long the virus can survive in manure-amended soil during winter months and help her advise swine producers on how to handle manure from a PEDv-positive herd when applying that manure to land.