Transmission of African Swine Fever Virus via carrier (survivor) pigs does occur

Abstract

We investigated whether ASF carrier pigs that had completely recovered from an acute infection with ASFV Netherlands ‘86, could transmit the disease to naive pigs by direct contact transmission. For this, we used pigs that had survived an ASFV infection, had recovered from disease, and had become carriers of ASFV. These clinically healthy carriers were put together one-by-one with naive contact pigs. Two of the twelve contact pigs developed an acute ASFV infection. Using the results of the experiment we quantified the transmission parameters βcarrier (0.039/day) and Tcarrier (25.4 days). With the survival rate of 0.3 for our ASFV isolate, these parameter values translate into the contribution of carriers to R0 in groups of pigs being 0.3. Further, we placed naive contact pigs in an ASFV contaminated environment. Here, no contact infections were observed. Our findings show that clinically healthy carriers can be a source of acute new infections, which can contribute to the persistence of ASFV in swine populations. The estimates that we provide can be used for modelling of transmission in domestic pigs and, in part, for modelling transmission in wild boar.