Transmission studies with African swine fever virus: Infections of pigs by airborne virus

Abstract

Eight recipient pigs developed African swine fever (ASF) after exposure to air drawn through ducting from 2 loose-boxes containing 16 donor pigs inoculated with ASF virus. A group of 6 pigs kept continuously on a platform 2·3 m above a group of 10 infected donor pigs also developed ASF. Of three pigs kept for 48 h on a platform above infected donor pigs which had been inoculated 3 to 5 days previously, one developed ASF. Recipient pigs exposed to donors at an earlier stage of incubation did not become infected, but all those exposed for 48 h to donor pigs in the later stages of acute disease became infected. After exposure for only 24 h, pigs did not develop ASF. The clinical signs in recipient and donor pigs were indistinguishable. Airborne virus was not detected by either biological or mechanical sampling procedures. The source of airborne virus was not determined. The failure of ASF virus to spread to sentinel control pigs housed in adjacent loose-boxes and other loose-boxes in the isolation unit suggests that the airborne spread of ASF is only likely to be a problem in intensive housing systems.