Stability of African swine fever virus in soil and options to mitigate the potential transmission risk

Understanding African swine fever virus (ASFV) transmission in a population is essential for strategies to minimize virus spread during an outbreak. ASFV can survive for extended periods of time in animal products, carcasses, and the environment. Recent studies have shown that wild boar demonstrate interest in carcasses at an advanced stage of decay and in the soil where the remains of wild boar once were. While ASFV nucleic acids have been found in the environment around infected farms, data on the survival of the virus in soil are scarce. We investigated different soil matrices spiked with ASFV-positive blood from infected wild boar to see if ASFV can remain viable in the soil beneath infected carcasses. Moreover, we tried different mitigation strategies that could be used in affected regions. As expected, ASFV genome detection was reliably possible over the full range of sampling days. Soil pH, structure, and ambient temperature played a significant role for the stability of infectious ASFV. Infectious ASFV was demonstrated in specimens originating from sterile sand for at least three weeks, and from ordinary beach sand for up to two weeks. In yard soil, infectious ASFV was demonstrated for one week, and in soil from a swampy area for three days. Virus was not recovered from two acidic forest soils. All risk mitigation experiments with citric acid or calcium hydroxide resulted in complete inactivation in our experimental setup. In conclusion, stability of infectious ASFV is almost non-existent in forest soils but rather high in sandy soils. However, given the high variability, treatment of carcass collection points with disinfectants should be considered for additional risk reduction. In this respect, biocidal nature and occupational safety have to be considered.