The ASFV-G-ΔI177L vaccine strain reverted to virulence during passaging and caused severe reproductive toxicity in pregnant sows, resulting in 43% stillbirths and only 17% piglet survival.
Is the ASFV-G-ΔI177L vaccine strain safe in pregnant sows and genetically stable during in vivo passaging?
The ASFV-G-ΔI177L vaccine strain is not genetically stable and reverts to virulence, indicating it is unsafe for use in ASF vaccines, particularly in pregnant animals.
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.
Born et al. (2025) studied this question. The ASFV-G-ΔI177L vaccine strain reverted to virulence during passaging and caused severe reproductive toxicity in pregnant sows, resulting in 43% stillbirths and only 17% piglet survival.