African swine fever is the cause of an epizootic that has affected the European Union since 2014. It causes significant losses in wild boar populations and in pig farms. The virus has not yet been detected in France but it is currently circulating in Italy, Poland and Germany. The disease, which cannot be transmitted to humans, has no treatment.
As part of its mandate as a national reference laboratory for African swine fever, the Swine Virology Immunology Unit (VIP) of ANSES’s Ploufragan-Plouzané-Niort laboratory inactivated the Georgia 2007/1 viral strain, which circulates currently in the European Union. When monitoring the effects of this thermal inactivation, an attenuated strain, derived from the Georgia strain, was fortuitously demonstrated. This only caused a slight fever in the infected animal, whereas infection with the Georgia strain is generally fatal in 100% of cases.
Promising results for a future vaccine
The team carried out a series of studies on this attenuated strain and confirmed the weakness of symptoms in most pigs inoculated with this virus intramuscularly or oronasally. Although the safety was not perfect, the survival rate was much higher than with the original viral strain.
« Intramuscular vaccination is the most widely used method in farms, says Marie-Frédérique Le Potier, head of the VIP unit. Vaccination by the oral route could make it possible to vaccinate wild boars using bait. This method was used for classical swine fever in the early 2000s and made it possible to eliminate the disease from areas where it was present in France. That is why we tested these two routes of administration from the start. »
Another promising result: infected pigs develop an immune response, which allows them to resist infection with African swine fever virus without showing any symptoms as early as two weeks after vaccination. These results were published in the journal Viruses in December 2022.
Adaptations to allow large-scale production by industrialists
ANSES scientists continued to work on the attenuated strain, in particular so that it could multiply in cell lines produced in vitro and not on cells to be taken from pigs, as was the case in the beginning. This step was a success, raising the possibility of producing the vaccine on a large scale. As a bonus, the strain of the virus thus produced caused fewer symptoms than the initial attenuated strain, while maintaining good efficacy.
Studies are still ongoing, particularly to ensure that this attenuated strain cannot be transmitted from one animal to another or become virulent again. The ability of the vaccine to prevent animals vaccinated and then exposed to the pathogenic African swine fever virus from retransmitting it will also be assessed.
Wild boars, the first potential target of vaccination
The vaccine developed by ANSES scientists has the advantage of not be produced by genetic manipulation, which would facilitate the authorization of its use in the wild. In effect, wild boars would probably be the first target for the vaccine in Western Europe. This species is the most affected and the presence of the virus in wildlife represents a risk for pig farms.
For these scientific discoveries to lead to effective industrial developments and in fine production of vaccines, it is essential to be able to transfer to veterinary pharmacy players. To do this, the laboratory filed a patent on the vaccine, published last August. ANSES is supported by the Technology Transfer Acceleration Company (SATT) Ouest Valorisation to promote the exploitation of this patent by interested industrialists.