ABSTRACT
African swine fever (ASF) has gained panzootic dimensions and commercial vaccines are still unavailable. Recently, a series of live attenuated vaccines has raised hope for an efficacious and safe vaccine, among them "ASFV-G-∆MGF". We tested the latter in an in vivo reversion to virulence study in accordance with International Cooperation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products guidelines. Upon forced animal passaging, a virus variant emerged that was associated with transient fever and an increased replication and shedding. However, all animals were healthy upon completion of the study and reversion to significant virulence was not observed. The genomic changes did not affect the recombination site but involved deletions and reorganizations in the terminal regions of the genome. Thus, our study underscores that in-depth safety characterization is needed for live ASF vaccines. For this particular candidate, additional studies should target long-term effects and transmission characteristics before thorough benefit-risk analysis can be carried out.
ABSTRACT
African swine fever (ASF) is a pandemic threat to the global pig industry and wild suids. A safe and efficacious vaccine could monumentally assist in disease eradication. In the past years, promising live attenuated vaccine candidates emerged in proof-of-concept experiments, among which was "ASFV-G-∆MGF". In our study, we tested the vaccine candidate in three animal experiments intramuscularly in domestic pigs and orally in wild boar. Further, a macrophage-grown vaccine virus and a virus grown on permanent cells could be employed. Irrespective of the production system of the vaccine virus, a two-dose intramuscular immunization could induce close-to-sterile immunity with full clinical protection against challenge infection. After oral immunization, 50% of the vaccinees seroconverted and all responders were completely protected against subsequent challenge. All nonresponders developed ASF upon challenge with two acute lethal infections and two mild and transient courses. The latter results show a lower efficiency after oral administration that would have to be taken into consideration when designing vaccination-based control measures. Overall, our findings confirm that "ASFV-G-∆MGF" is a most promising vaccine candidate that could find its way into well-organized and controlled immunization campaigns. Further research is needed to characterize safety aspects and define possible improvements of oral efficiency.
