Zoonosis: Pigs and Wild Boars Are Behind the Increased Circulation of the Hepatitis E Virus

The spread of the hepatitis E virus, which is emerging in Europe, is on the rise. Autochthonous cases are appearing, resulting from zoonotic transmission from pigs and wild boars to humans. Bulgarian researchers have assessed the viral seroprevalence in their country. HEV is one of the least well-known hepatitis viruses. However, its global spread is undisputed and has been on the rise in recent years. It is even one of the leading causes of acute hepatitis worldwide. Infection with the hepatitis E virus generally resolves spontaneously in healthy human patients. However, immunocompromised individuals (particularly pregnant women), those with co-infections, or transplant recipients may develop a fulminant infection with a high risk of progressing to chronic hepatitis. This virus therefore warrants close monitoring, particularly in animal populations. In fact, hepatitis E is a viral disease with proven zoonotic potential for some of its genotypes. The main viral reservoirs are domestic pigs and wild boars. HEV transmission within a herd occurs naturally through direct contact with infected animals or the feces of sick animals, or through contaminated water or food sources. Animals can contract the virus at different stages of their development. Most studies show that pigs become infected between 8 and 15 weeks of age, and some remain positive until slaughter.

Meat consumption that is undercooked, as well as occupational exposure, are key factors in the spread of HEV to humans.

Over the past decade, locally acquired cases resulting from the zoonotic spread of the virus—primarily genotype 3—have emerged and are on the rise in developed countries, particularly in Europe. HEV is considered an emerging pathogen in these regions, with seroprevalence in pig herds ranging from 30 to 100 percent. In Norway, 90% of the herds studied and 73% of individual serum samples tested positive. In Italy and Spain, 97.43% and 97.65% of herds, and 50.21% and 41.9% of serum samples, respectively, tested positive for HEV. However, Europe-wide data remain incomplete. To identify associated risk factors and assess future viral trends at the European level, a detailed analysis of the virus’s ecology, dynamics, and distribution is necessary. This is what was done in Bulgaria. Bulgarian researchers studied the distribution and prevalence of HEV in pigs—and, for the first time, in wild boars—over a three-year period in their country. Between 2017 and 2019, 433 serum samples from 19 different pig farms and one slaughterhouse, as well as 32 samples collected from wild boars, were collected and analyzed. Overall, the results show a seroprevalence of HEV of 60% in domestic pigs and 12.5% in wild boars. The year 2019 saw a notable increase in infections compared to the previous two years. This study is the first to show that the hepatitis E virus circulates among wild boars in Bulgaria. The results of the IgG seroprevalence among suids and Bulgarian pigs confirm the circulation of the viral infection in these two species, thereby highlighting a significant risk of transmission of this zoonotic virus through raw or undercooked meat consumption and direct contact with these animals. Thus, domestic pigs and wild boars could be responsible for the increase in HEV transmission in the country. The more frequent detection of anti-HEV antibodies among veterinarians and pig farmers attests to the disease’s zoonotic potential. However, follow-up studies—particularly those aimed at confirming zoonotic transmission of this virus—and the genotypic characterization of HEV found in pigs, wild boars, and humans would provide a more accurate picture of the disease’s circulation.