Natural inactivation of African swine fever virus in tissues: Influence of temperature and environmental conditions on virus survival

Abstract

African swine fever virus can be transmitted through direct contact with infected animals and their excretions, or indirect contact with contaminated fomites. Risk assessment of the disease spreading requires quantitative knowledge about time and conditions needed for its inactivation in various material of pig origin. In this study we aimed to assess ASFV stability in naturally contaminated tissues during storage in selected environmental conditions. Virus half-life (T ½) and decimal reduction rate (D-value) were determined for temperatures relevant for freezing, chilling and ambient storage. A nonlinear regression model was developed to predict T ½ for temperatures between −20 °C and +23 °C. The half-life of the infectious ASFV in tissues ranged from 31.95 days at −20 °C to 0.38 days at +23 °C, with estimated D-values between 106.12–1.27 days, respectively. In order to assess the influence of environmental conditions on the rate of ASFV inactivation in decomposing tissue, viral half-life was evaluated at +4 °C and +23 °C in tissues stored within various matrices, mimicking possible natural conditions. Water, soil and leaf litter presence induced significantly faster ASFV inactivation. Straw, hay and grain provided stable conditions and prolonged virus viability for a considerable amount of time. In contrast to viable virus reduction over time, no change in ASFV DNA concentration was detected by real-time PCR. Based on estimated half-life values, the investigated tissues are predicted to remain infectious for 353–713 days at −20 °C, 35–136 days at +4 °C, and from 9 to 17 days at +23 °C. These data provide valuable information for the ASF preventive measures improvement.