Evaluation of Whole Carcass Composting as a Mortality Disposal Option for African Swine Fever Virus-Infected Swine

Abstract

African swine fever (ASF) epizootic outbreaks often result in the deaths of large numbers of swine either through confirmed or suspected disease or depopulation for outbreak control. Identification of effective biosecure livestock mortality disposal methods, capable of inactivating ASF virus (ASFV) in contaminated carcasses, remains an important component for development of localized outbreak response and recovery plans. In this study, we evaluated ASFV inactivation and viral DNA degradation during composting of ASFV-infected swine carcasses in an Animal Biosafety Level 3-Ag (ABSL3-Ag) high-containment vivarium utilizing virus isolation (VI) and real-time polymerase chain reaction (RT-PCR). Four ASFV-infected pigs, approximately 54 kg, were composted for 37 days in a static, nonaerated windrow assembled using wood chips, horse manure, and pine shavings as the primary sources of carbon. The windrow daily temperature was sustained at ≥55°C for 18 days. Spleen samples, collected over 28 days, were negative for infectious ASFV by virus isolation on day 5 but remained positive for ASFV DNA by RT-PCR through day 28. At the conclusion of the study, bone marrow, muscle, and pinna samples were collected from composted carcasses, in addition to carbon materials in the windrow. No infectious ASFV was detected by virus isolation in any of the decomposed tissues or carbon samples. However, ASFV DNA remained detectable in all swine tissues (n = 36) and in 14/16 sentinel carbon samples at the end of the study, indicating that positive detection of ASFV DNA did not correlate with virus infectivity. In conclusion, infectious ASFV was rapidly eliminated in ASFV-infected swine during composting of whole carcasses by day 5, coinciding with a temperature increase in the compost pile to ≥55°C.