A troubling fact: genotype 3 has also been identified in the same geographic areas in pigs and, to a lesser degree, in wild boar and deer. So could there be a potential zoonotic reservoir of the virus, allowing transmission from animals to humans? This remains to be seen...  

“What happens between pigs and humans? That’s the question we’ve been trying to answer for the past five years, in collaboration with the ISP”, Étienne Thiry continues. “For the time being, we don’t know exactly if the virus first appeared in humans or pigs”. With the help of an American specialist, the laboratory in Liège analysed phylogenetic data to establish the virus’ family tree, based on current knowledge, in order to go back as far as possible in time. It wasn’t easy because it belongs to the very complex Hepeviridae family, which is found in camels, rodents, and bats. The researchers nevertheless managed to go back approximately 1 million years to find an ancestor common to hepevirus in mammals and birds. The dichotomy occurred later, but no-one knows whether pig or humans were infected first.   

One thing is certain, genotype 3 hepatitis E also affects pigs. The team from Liège carried out a survey among Belgian pig farmers, in order to determine how many animals were infected. The verdict: 93 % of pig farms tested positive and 73 % of pigs were affected. “We weren’t expecting such a high prevalence! Especially compared with 14 % seropositivity in humans according to the Flemish study”, Étienne Thiry points out. “As for pigs, the virus is found almost everywhere, compared with a low incidence in humans. How does this virus pass from animals to humans?”

To find out, the laboratory first studied the presence of hepatitis E in wildlife (1) in collaboration with the Department of Wildlife Health and Pathology under Prof. A. Linden. It established that 34 % of wild boars were positive, compared with 1 to 3 % of deer and roe deer. “We therefore – quite confidently – suggested that there were two identified animal reservoirs in Belgium: domestic pigs and wild boar”. Once again, it is impossible to accurately determine who infected who in the beginning. “Even if it is very difficult to demonstrate, we can put forward the hypothesis that this virus, which has existed for hundreds of thousands of year, must have initially been present in wildlife. In the beginning, pigs were practically all wild. In fact, the pig is a sort of domesticated wild boar. But does this virus come from pigs or was it transmitted to them by humans? We can’t answer this question”, Étienne Thiry repeats.  

He and his team nevertheless wanted to determine whether the wild boar virus could inoculate pigs. Considering the prevalence of the disease in farms, it was no mean feat to find “clean” animals. They had to go to France, to the Breton commune of Ploufragan, where ANSES (Agence nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail) has an adjoining animal house, with biosecurity level 3, where a herd of pigs can live protected from infection. “We carried out two series of experiments”, the professor explains. “First to show that the wild boar virus is transmitted to pigs, and then transmitted from pig to pig. It isn’t enough to demonstrate a probability of introduction, it is also necessary to ensure that once the virus has multiplied, it can be infectious again for the others and thus establish itself in a pig population. This is where we are currently at”.  

(1)Belgian Wildlife as Potential Zoonotic Reservoir of Hepatitis E virus, in Transboundary and Emerging Diseases (2015).