A study by Vall d'Hebron and UB suggests wild boars could be a potential source of hepatitis E transmission to humans in the Barcelona metropolitan area

In recent decades, wild boar populations have increased in urban areas of Barcelona and other parts of Catalonia. This wild animal is an important reservoir of the hepatitis E virus, the causative agent of this disease that affects more than twenty million people annually, according to the World Health Organization (WHO). Now, a team from the Faculty of Biology, the Institute of Biodiversity Research (IRBio) at the University of Barcelona, and the Faculty of Veterinary Medicine at the Autonomous University of Barcelona has identified a significant molecular similarity between the hepatitis E virus (HEV) strains in wild boars from the Barcelona metropolitan area and those found in people from this region. According to the researchers, these findings suggest that these animals could be a source of human hepatitis E infections in the metropolitan area. The study also involved researchers from the Transfusional Medicine Group at the Vall d'Hebron Research Institute (VHIR).

Jordi Serra-Cobo, professor at the Faculty of Biology and researcher at IRBio, co-led the research with María Isabel Costafreda, professor in the Department of Genetics, Microbiology, and Statistics, and researcher at the Institute of Research in Nutrition and Food Safety at UB (INSA) and the Biomedical Research Centre in Liver and Digestive Diseases (CIBEREHD).

The study, published in Science of The Total Environment, also involved Abir Monastiri and Marc López-Roig from IRBio, and María I. Costafreda, along with other researchers from the Blood and Tissue Bank of Catalonia, Vall d'Hebron Research Institute (VHIR), the University of Lleida, and the Wild Fauna Ecopathology Service (UAB).

An endemic virus among wild boar populations

The Barcelona metropolitan area consists of thirty-six municipalities, covering 636 km² and home to nearly 3.2 million people. This region, which includes the Collserola Natural Park — a peri-urban Mediterranean forest of eight thousand hectares surrounded by urban areas — has a wild boar population density ranging from five to fifteen individuals per square kilometer.

In the study, the researchers analyzed the feces of 312 wild boars collected in this region between 2016 and 2021, seven of which tested positive for the virus. Comparing these samples, along with six additional samples from a previous study, allowed researchers to establish “a close phylogenetic relationship” — that is, evolutionary relatedness and genetic similarity — between the HEV strains from the wild boars and those found in blood donors from the area. The researcher, a member of the Department of Evolutionary Biology, Ecology, and Environmental Sciences at UB, details that “all isolated viruses were classified within genotype 3 of HEV”.

Furthermore, the samples from infected wild boars came from non-adult individuals, which, according to the researchers, indicates the endemic — that is, habitual and permanent — nature of HEV in the wild boar population in the metropolitan area through young individuals. In this regard, they argue that “the lack of HEV detection in adult boars suggests that young animals are exposed to the infection 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 of this region”.

A global public health issue

The increase in the presence of wild boars in urban areas of Barcelona, as well as in cities like Lugo, Rome, Berlin, Genoa, and Hong Kong, is mainly due to factors such as the loss of natural habitats caused by human activities. “Since wild boar urbanization — the presence and adaptation of wild boars in urbanized environments — is a global phenomenon, increasing and expanding, the results of this study should be useful in developing and establishing monitoring, surveillance, and potentially control programs for HEV both in the Barcelona metropolitan area and in other urban areas worldwide,” explains Serra-Cobo.

It is important to note that, as explained by the specialists in the article, “while most human cases of hepatitis E are mild, HEV infection causes approximately fifty thousand human deaths annually, and is particularly severe in pregnant women, with mortality rates of up to 30%, and it can also be transmitted to newborns.”

Prevention measures and information

Among the measures to prevent the transmission of hepatitis E virus to the public, the researchers highlight the importance of avoiding “contact with wild boars, as well as not eating their meat raw or undercooked”. In cases of contact, such as with hunters or forest rangers, they recommend washing hands with soap and water. “This practice removes the virus's lipid coating and inactivates it,” they emphasize.

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

In this sense, they recommend avoiding contact between household animals and the feces of wild animals, and installing systems to prevent wild boars from tipping over trash bins. They also stress that “it is important to inform the public about the risk factors for hepatitis E transmission from wild boars, both to people and to pets”.

Long-term wild boar monitoring

The IRBio research group at the University of Barcelona is conducting another study, now in an advanced phase, to better understand the dynamics of HEV infection in the wild boar population in the Barcelona metropolitan area. Moreover, the researcher emphasizes the “crucial importance” of long-term monitoring and surveillance 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, due to climate change and anthropogenic factors.”