African swine fever virus vaccine strain Asfv-G-∆I177l reverts to virulence and negatively affects reproductive performance
Erwin van den Born, Ferenc Olasz, István Mészáros, Eszter Göltl, Barbara Oláh, Jui Joshi, Emma van Kilsdonk, Ruud Segers, Zoltán Zádori
Abstract
ASFV-G-ΔI177L is a modified-live African swine fever virus (ASFV) strain that has been incorporated into a commercially available vaccine. Its safety in pregnant sows and genetic stability in an in vivo passaging experiment were investigated. Upon inoculation of two pregnant sows with ASFV-G-ΔI177L, one developed moderate ASF-related clinical signs. In terms of reproductive performance, 43% of the offspring was born dead and the live-born piglets developed ASF-specific clinical signs, became viremic, and only 17% survived until the end of study. During passaging in pigs, ASFV-G-ΔI177L reverted to virulence with severe ASF-specific clinical signs at passages 3 and 4, associated with increased viremia. Whole genome sequencing identified C257L mutations as a potential driver of increased replication fitness and virulence. The data show that ASFV-G-ΔI177L is not genetically stable and, therefore not safe for use in ASF vaccines and suggest that ASF vaccine candidates should be tested for safety in pregnant animals.