Results
Recovery of ASFV from yard soil on macrophages (Experiment 1)
In this pilot experiment yard soil was spiked with blood from ASFV infected wild boar and stored for four weeks at 25°C or 4°C. A blood-only control was carried along under the same conditions.
Regarding the blood-only control stored at 4°C, a high variability of the determined virus titers was observed during the first 48 hours (Figure 3). Titers of the 3 biological replicates ranged between 3.75 log10 HAD50/mL and 7.00 log10 HAD50/mL after an incubation time of six hours at 4°C. Such a variation did not reoccur at later time points or in the blood-only control stored at 25°C. In general, virus titers in pure blood decreased clearly after two weeks storage at either temperature. However, the blood-only controls (4°C and 25°C) remained infectious over the entire observation period.
Virus titers in yard soil spiked with infectious blood and stored at 4°C or 25°C generally decreased within the first 72 hours (Figure 3). In contaminated yard soil stored at 25°C no infectious virus was detectable after 72 hours. After one week, however, a high variability between the biological replicates was observed in yard soil at both storage temperatures, with virus titers up to 5.50 log10HAD50/mL at 25°C. Hence, we found that ASFV remained infectious in yard soil (pH 6.7) for up to 7 days at both temperatures. After two weeks, contaminated yard soil was clearly negative for infectious virus until the end of the study.
Irrespective of the storage temperature, ASFV genome copy numbers were constant over time in the blood-only control and in yard soil samples.