There are 4 genotypes of Hepatitis E viruses, of which HEV1 and HEV2 can only infect humans, while HEV3 and HEV4 can infect humans and certain mammals such as wild boars, pigs, deers and rabbits. In recent years, an increasing number of zoonotic cases of HEV3 and HEV4 have been reported in developed countries (HEV3 mainly affects European countries, while HEV4 is prevalent in Asia). The main sources of zoonotic cases are raw and undercooked meat products or contact with infected animals. Interhuman transmissions have also been reported. Older individuals with coexisting illnesses are typically susceptible to infection. In many cases (60%) liver cirrhosis may occur at the affected individuals.

Seroprevalence studies in various European countries have reported variable and sometimes high rates of anti-HEV Ig G among the general population and blood donors. A recent meta-analysis on HEV seroprevalence in Europe from 2003 to 2015 reported estimates ranging from 0.6% to 52.5%. The variability can be attributed to the performance of anti-HEV assays used, some geographical-environmental factors (including human behaviour, regional dietary habits, presence of animal reservoirs), and the cohort under investigation.

In 2015, a project was launched in Italy to investigate the prevalence of HEV among blood donors. More than 10.000 samples from all regions were tested. The project found a total of 8.7% IgG rate and 0.5% IgM positive samples. Overall, IgG prevalence was higher in males and the spatial distribution was not even (between 2.2% and 22.8% per region). Overall, the prevalence of anti-HEV IgG in Italy in 2015 was not abnormally high compared to other European countries (Netherlands 27%, France 22.4%, Spain 19.9%). The results of the Italian regions were compared with the level of pig density at regional level, but no correlation was found: in the most intensive pig-breeding areas, such as Lombardy, Piedmont, the anti-HEV IgG prevalence rate in samples was 6-8%. The results of the project suggest that the elevated anti-HEV prevalence rate may be due to the consumption of inadequately prepared, heat-treated meat and other environmental influences.

Due to the increasing number of HEV cases, research groups and the BfR (German Federal Institute for Risk Assessment) conducted a study to investigate the prevalence of HEV RNA in pork livers and pork meat products, in order to assess the risk of HEV infection through food consumption in Germany. 131 pork products were collected from grocery stores and butcher shops and screened for HEV RNA. Overall, 10% of the samples were positive for HEV, including pork livers (5%), spreadable liver sausages (13%) and liver pâté samples (15%). Sequence analyses indicated that the large majority of HEV strains belonged to subtype HEV-3c, the most frequent subtype in Germany. Compared with earlier studies, the results indicate that the prevalence of Hepatitis E virus in foods containing pork liver has remained relatively stable and very high in Germany for the last ten years. The infectivity of the virus was not investigated. Thus, the detected virus may have been already inactivated by heating processes during food production. The limitation of the study is the sample size, however, it can be said that HEV is present in pork products and explains the high rate of HEV infections, especially in high-risk groups (over 50 years).

The results also demonstrate the importance of the "One Health" approach, and in this case, the presence of a licensed HEV vaccine would be very important. In addition, it would be useful to inform consumers about the importance of heat treatment. According to the NNK data, the number of HEV infections in Hungary has also been on the rise since 2015, with the annual number of cases increasing from 166 to 262 in 5 years.