# A dual-gene-deleted ASFV Lv17/WB/Rie1-ΔCD candidate administered orally to wild boar confers DIVA-compatible protection against virulent challenge

## TL;DR

Researchers developed a safer oral vaccine for African swine fever that protects wild boar and allows for distinguishing vaccinated from infected animals.

## Contribution

The study introduces a dual-gene-deleted ASFV vaccine candidate with improved safety and DIVA compatibility for oral administration.

## Key findings

- The ΔCD vaccine induced sterilizing immunity in 5 out of 6 animals in the high dose group.
- Quantitative PCR showed over 1000-fold reductions in viral genome copies in vaccinated animals.
- DIVA ELISA reliably distinguished vaccine-induced antibodies from infection-derived responses.

## Abstract

African swine fever (ASF) continues to expand worldwide. Recent detection in wild boar in Spain highlights the urgent need for effective control tools, with oral vaccination as a key priority. Following previous evaluation of the attenuated Lv17/WB/Rie1 strain, we assess an improved derivative, Lv17/WB/Rie1-ΔCD, lacking EP402R (CD2v) and EP153R, replaced by GFP to abrogate haemadsorption and enable Differentiating-Infected-from-Vaccinated-Animals (DIVA) diagnostics. Vaccinated animals received either a single high dose (104 TCID₅₀) or a prime and re-exposure regimen (102 TCID₅₀ plus a 104 TCID₅₀). Animals were challenged intramuscularly with the virulent Armenia07 genotype II strain. The ΔCD vaccine was well tolerated, inducing only transient low-grade fever. Prime–re-exposure vaccination induced earlier seroconversion (mean 12 ± 4 dpv) and sterilizing immunity in 5/6 animals in the high dose group. Overall protection reached 90%, while all unvaccinated controls died within 7 days. Quantitative PCR revealed >10³-fold reductions in viral genome copies in blood and tissues versus controls. DIVA ELISA reliably distinguished vaccine-induced antibodies from infection-derived responses. These findings identify Lv17/WB/Rie1-ΔCD as a safer oral ASFV vaccine candidate, addressing concerns raised with the parental Lv17/WB/Rie1 by increasing attenuation and supporting multi-gene deletion strategies. Further studies on safety, transmission, genetic stability, and environmental behaviour are required before large-scale field trials.