Introduction
In the last decade, African swine fever (ASF) has reached an unprecedented geographical spread affecting wild boar and domestic swine in large parts of Europe and Asia, as well as several areas in Africa (Dixon et al., 2020). The notifiable disease of suids can be accompanied by signs of a viral hemorrhagic fever in domestic pigs and Eurasian wild boar (Sanchez-Vizcaino et al., 2015). The virus is transmitted directly between infected swine and wild boar by the oro-nasal route, indirectly by ingestion of contaminated meat. It can also be transmitted by competent vectors, i.e. soft ticks of the genus Ornithodoros . They play an important role in Africa, but only in a few areas outside this continent (Costard et al., 2013). Despite its limited host range and non-existent zoonotic potential, the socio-economic impact is high and many stakeholders are involved (Gallardo et al., 2015).
During the first years of the current epidemic that started in Georgia in 2007, infections were mainly seen among pig farms with generally low biosecurity, and with incidental spill over to the wild boar population. In the EU, however, the infection survived in the wild boar population independently from outbreaks in domestic pigs (Chenais et al., 2019).
For the transmission among wild boar, carcasses and the contaminated habitat seem to play a crucial role, together with humans as long-distance spreaders (Chenais et al., 2019).
So far, there are only a few cases in the current European outbreak where the disease was completely eradicated from a country’s wild boar population. One case is the Czech Republic, where the control measures successfully applied there are used as guide for ongoing efforts elsewhere (Dixon et al., 2020). The other case is Belgium which is very close to becoming free of ASFV as no new wild boar cases have been detected (fasfc.be, 2020). Both countries followed EU policy to keep the virus concentrated in one zone as much as possible.
An integral part of the control strategy is to search for and remove carcasses as a potential virus source. In this context, the question was raised whether the soil under a removed wild boar carcass should be also removed or treated to prevent virus transmission to other wild boar rooting in the contaminated soil. It was shown that viral genome can be detected in such soil (Arvo Viltrop and Imbi Nurmoja, personal communication) and in order to minimize the transmission risk, simple physical measures such as loosening the soil, but also the application of disinfectants were intensively debated. Commercial disinfectants as well as lime products, i.e. quicklime and limewater (an aqueous solution of calcium hydroxide), were considered as possible options.
Consequently, our experiments began simply to establish a protocol to isolate ASFV from soil samples but evolved over time as we obtained more data. We set out to determine basic values of the stability of ASFV in soil matrices and how infectivity could be reduced.