VHA et VHE, une épidémiologie en évolution, une prophylaxie à adapter

Abstract

Hepatitis A virus (HAV) and hepatitis B virus (HBV) are two non-enveloped RNA viruses, which cause acute hepatitis with no progression to chronic liver disease and no chronic carriage. This is why, for their survival, these two viruses have a particularly efficient transmission mechanism: the faecal-oral route. Despite this similarity, there are significant differences between HAV and HEV with respect to their viral characteristics, their epidemiology and their treatment. HAV is a member of the Picornaviridae, while HEV belongs to the small Hepeviridae family. Although several genotypes have been identified for these two viruses, only one serotype is recognized for each. For HAV, humans are the only reservoir. The infection is associated with poor sanitation. Socioeconomic improvements and better hygiene standards have reduced the transmission of HAV in developed countries. The mean age of exposure has increased, resulting in large numbers of teenagers and adults becoming susceptible to the virus. Unlike HAV, HEV is zoonotic. The virus is found in the faeces of many animals although pigs seem to be the main reservoir. Hepatitis E occurs predominantly in developing countries, resulting in large water-born epidemics. Person-to-person transmission is less frequent. In developed countries, most HEV infections are thought to be imported. In the last few years, increasing numbers of sporadic cases have been described in indigenous patients, while the seroprevalence ranges from 1 to 5%. This suggests that HEV may be more prevalent than previously considered in industrialized countries. Immunization with inactivated HAV vaccine results in highly effective, rapid and long-lasting immunity. The changing epidemiology of HAV infections in many countries should lead to a review of vaccination strategies. Several vaccines against HEV are currently undergoing evaluation in clinical trials.