Infection with African swine fever virus (ASFV) causes a highly lethal hemorrhagic disease in domestic and Eurasian wild pigs. Thus, it is a major threat to pig populations worldwide and a cause of substantial economic losses. Recently, less virulent ASFV strains emerged naturally, which showed higher experimental virulence in wild boar than in domestic pigs. The reason for this difference in disease progression and outcome is unclear but likely involves different immunological responses. Unfortunately, besides the importance of CD8α+ lymphocytes, little is known about the immune responses against ASFV in suids. Against this background, we used a multicolor flow cytometry platform to investigate the T-cell responses in wild boar and domestic pigs after infection with the moderately virulent ASFV strain “Estonia2014” in two independent trials. CD4–/CD8α+ and CD4+/CD8α+ αβ T-cell frequencies increased in both subspecies in various tissues, but CD8α+ γδ T cells differentiated and responded in wild boar only. Proliferation in CD8α+ T cells was found 10 days post infectionem only. Frequencies of T-bet+ T cells increased in wild boar but not in domestic pigs. Of note, we found a considerable loss of perforin expression in cytotoxic T cells, 5 and 7 dpi. Both subspecies established a regulatory T-cell response 10 dpi. In domestic pigs, we show increasing levels of ICOS+ and CD8α+ invariant Natural Killer T cells. These disparities in T-cell responses might explain some of the differences in disease progression in wild boar and domestic pigs and should pave the way for future studies.

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.