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. 2025 Mar 6;10(1):46.
doi: 10.1038/s41541-025-01099-9.

African swine fever virus vaccine strain Asfv-G-∆I177l reverts to virulence and negatively affects reproductive performance

Erwin van den Born  1 , Ferenc Olasz  2   3 , István Mészáros  2 , Eszter Göltl  2   3 , Barbara Oláh  2 , Jui Joshi  1 , Emma van Kilsdonk  1 , Ruud Segers  1 , Zoltán Zádori  4   5
Affiliations

African swine fever virus vaccine strain Asfv-G-∆I177l reverts to virulence and negatively affects reproductive performance

Erwin van den Born et al. NPJ Vaccines. .

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.

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Conflict of interest statement

Competing interests: Zoltán Zádori is the owner of Avirtransvac Ltd., which is a contractual partner of MSD Animal Health. István Mészáros carries out custom orders for Avirtransvac Ltd. All other authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Pre- and post-farrowing data of the pregnant sow study.
A viremia in ASFV-G-ΔI177L-inoculated sows (group I) presented as ASFV-specific Ct values plotted as a function of dpi. B Rectal temperatures of the group I sows and the PBS-inoculated control sows (group II). C The sum of ASF-specific clinical signs scores recorded for the sows in both groups. D average rectal temperatures of piglets born from groups I and II sows. E viremia in the four surviving piglets born in group I presented as ASFV-specific Ct values plotted as a function of days post-farrowing.
Fig. 2
Fig. 2. ASFV-G-ΔI177L infection-related data obtained in the reversion to virulence study.
P1–P4 indicate the passage level during the in vivo passaging experiment. A The sum of the ASF clinical signs scores recorded during each passage. B Average rectal temperature; C Average level of ASFV viremia in each passage presented as Ct values plotted against dpi. D Survival rate of the pigs after inoculation with ASFV-G-ΔI177L P4 virus diluted at different levels.
Fig. 3
Fig. 3. Alignment of the C257L sequence identified in the different passages.
P1 animal 4644; P2 animal 4647, P3 animal 4648, P4 animal 4650.
See this image and copyright information in PMC

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