Eight recipient pigs developed African swine fever after exposure to air drawn through ducting from two loose boxes containing 16 donor pigs inoculated with the virus. A further group housed on a platform 2.3 metres above infected pigs also developed the disease. Airborne transmission required donors in the later stages of acute disease. This is the first controlled demonstration of the ASFV airborne route.
The study has held up. Olesen and colleagues repeated the demonstration in 2017 with a recent European isolate from Poland, finding that pigs exposed by intranasal inoculation, by direct contact and by aerosol all developed acute disease. De Carvalho Ferreira and colleagues quantified the airborne virus load in 2013. Li and colleagues documented a complete transmission chain between two piggeries under field conditions in 2023, with deposited dust as the intermediate step. Nearly fifty years separate the first and the most recent, and the route has been confirmed at every stage.
The disease stage condition is the detail with the most operational weight. If airborne transmission requires donors in the later stages of acute disease, then the airborne risk from a given building rises as infection progresses within it, and the window in which air handling matters most is the window in which the herd is most obviously sick. Combined with the placement of ASFV in the short distance category, that describes a pathogen whose airborne risk is principally about air movement within and between buildings on a site rather than about the neighbourhood.