Barcelona’s wild boar population linked to hepatitis E infections in humans

Over the last few decades, wild boar populations have increased in the urban areas of Barcelona and in other parts of Catalonia. This wild animal is an important reservoir of the hepatitis E virus, the disease causative agent that affects more than 20 million people every year, according to the World Health Organization (WHO). Now, a team from the Faculty of Biology, the Institute for Research on Biodiversity (IRBio) of the University of Barcelona and the Faculty of Veterinary Medicine of the Universitat Autònoma de Barcelona (UAB) has identified a relevant molecular similarity between the hepatitis E virus (HEV) strains of wild boars in the metropolitan area of Barcelona and the citizens of this area. According to the researchers, these data suggest that these animals could be a source of human hepatitis E infections in the metropolitan region.

Jordi Serra-Cobo, lecturer at the UB’s Faculty of Biology and researcher at IRBio, has co-led the study with Maria Isabel Costafreda, lecturer at the Department of Genetics, Microbiology and Statistics, and researcher at the UB Nutrition and Food Safety Institute (INSA) and the Liver and Digestive Diseases Networking Biomedical Research Centre (CIBEREHD). Jordi Serra-Cobo warns that “the results should serve to take preventive measures and be watchful against possible transmission of the hepatitis E virus from wild boars to the citizens of the Barcelona metropolitan area”. The study, published in Science of The Total Environment, also involved Abir Monastiri and Marc López-Roig (IRBio), and Maria Costafreda, along with other researchers from the Banc de Sang i Teixits (Blood and Tissue Bank of Catalonia), the Vall d’Hebron Research Institute (VHIR), the University of Lleida and the Wildlife Ecopathology Service (UAB).

An endemic virus in the wild boar population

The metropolitan area of Barcelona is made up of thirty-six municipalities, spread over 636 km² and populated by around 3.2 million people. This area, which includes the Collserola natural park — a peri-urban Mediterranean forest of 8,000 hectares, surrounded by urban centres — has a wild boar population density of between five and fifteen individuals per square kilometre.

In the study, the researchers analysed the faeces of 312 wild boars collected in this region between 2016 and 2021, seven of which tested positive for the presence of the virus. The comparison of these samples, together with six additional samples from a previous study, has made it possible to establish “a close phylogenetic relationship” — that is, evolutionary kinship and genetic similarity — with the HEV strains from blood donors in this area. Serra-Cobo, a member of the UB’s Department of Evolutionary Biology, Ecology and Environmental Sciences, notes that “all the isolated viruses were classified within genotype 3 of HEV”.

Moreover, the wild boar samples with the virus belonged to non-adult individuals, which, according to the researchers, indicates the endemic — that is, habitual and permanent — maintenance of HEV in the wild boar population of the metropolitan area by young individuals. In this sense, they explain that “the lack of HEV detection in adult wild boars suggests that young animals are exposed to infection by the virus in the first years of life, while adults have already overcome the infection and are protected from reinfection”. “This suggests that the virus is endemic in the wild boar population in this region”, add the researchers.

A global public health problem

The growing presence of wild boars in the urban areas of Barcelona (but also in other cities such as Lugo, Rome, Berlin, Genoa or Hong Kong) is mainly due to factors such as the loss of natural habitats induced by human activities. “Given that the synurbization — the presence and adaptation of wild boar in urbanized environments — of wild boar is a global phenomenon, which is increasing and expanding, the results of this study should be useful to develop and establish programmes for monitoring, surveillance and, eventually, control of HEV both in the metropolitan area of Barcelona and in other urban areas of the world”, says Serra-Cobo.

In the article, the experts explain that “although most human cases of hepatitis E are mild, HEV infection causes approximately 50,000 human deaths each year, and is particularly serious in pregnant women, with mortality rates of up to 30%, and can be transmitted to infants”.

Prevention and information measures

Among the measures to prevent transmission of the hepatitis E virus to the public, the researchers stress the importance of avoiding “contact with wild boars, as well as not eating their raw or undercooked meat”. In cases where contact has occurred, such as with hunters or forestry agents, they recommend washing hands with soap and water. “This practice removes the lipid envelope of the virus and inactivates it”, they note.

They also highlight other measures related to pets. “Wild boars can invade the streets of central Barcelona, where they find food in rubbish bins or urban gardens. These spaces are frequented by dogs and cats, which can become infected with wild boar faeces and can contribute to spreading the infection to citizens”, warns Jordi Serra-Cobo.

In this regard, they recommend preventing household pets from coming into contact with wild animal faeces and installing systems to prevent wild boars from knocking over waste containers. The researchers also note that “it is also important to tell the public about the risk factors for the transmission of hepatitis E from wild boars, either to humans or to pets”.

Long-term monitoring of wild boars

The IRBio research group at the UB has another study underway to determine the dynamics of hepatitis E virus infection in the wild boar population in the metropolitan area of Barcelona. The researcher also stresses the “fundamental importance” of a long-term follow-up and monitoring of the health status of the wild boar population, “especially at a time when the structure and functioning of ecosystems are changing at an unprecedented rate, as a result of climate change and anthropogenic factors”.