Protective assessment of oral immunization against genotype II using a new ASFV live attenuated vaccine prototype in wild boar

Introduction

African Swine Fever (ASF) is a highly lethal hemorrhagic viral disease affecting domestic and wild suids. Its rapid spread across Europe and Asia, together with the lack of effective treatment or authorized vaccines in Europe, has led to significant economic losses. Since wild boars pose a major control challenge, the development of a safe and effective oral vaccine is crucial due to handling difficulties.

Methods

This study, performed in BSL-3 facilities, evaluated the efficacy of a new DIVA vaccine candidate Lv17/WB/Rie1-ΔCD-ΔFJ, derived from the naturally attenuated strain Lv17/WB/Rie1 in wild boar by oral route. Ten wild boars were twice orally vaccinated on days 0 and 18 and challenged intramuscularly on day 36 post-vaccination with the highly lethal Armenia 2007 strain (100% mortality in controls) . A non-vaccinated control group was challenged in the same conditions. Animals were under continuous monitoring throughout the experiment including assessment of clinical signs, rectal temperature, viremia levels and immune response over a 62-day period.

Results

The oral vaccine candidate showed an overall favourable safety profile, with no adverse clinical signs observed during the experimental period, presenting low and transient viremias (37.84 ± 5,97). Detectable vaccine-induced antibodies were observed in 7/10 animals; all seropositive animals survived challenge, whereas seronegative animals and all controls succumbed to infection. Following challenge, vaccinated animals exhibited lower viremia levels than controls (21.02 ± 6.66) and low clinical scores (CS=0.6 ± 1.67), indicating partial protection against disease.

Conclusions

This vaccine candidate reduced viremia and conferred partial protection against virulent challenge. However, as this is an initial experimental evaluation, further studies and field trials are required to confirm these findings and rule out reversion to virulence. Despite these limitations, the results support the continued development of this attenuated vaccine as a potential tool for ASF control.