Epidemiology of viral hepatitis.

Despite virological complexity exacerbated by the progress made by molecular biology viral hepatitis has kept an unchanged epidemiological bipolarity over the last 50 years, contrasting hepatitis transmitted feco-orally to hepatitis mainly transmitted by blood. The former due to he hepatitis A virus (HAV) and the hepatitis E virus (HEV), bring about acute symptoms which can be severe, but are never chronic. Both viruses are capable of provoking epidemics of sometimes important proportions in the case of non immune or partially immune populations. The second kind of hepatitis, due to hepatitis B (HBV) and hepatitis delta (HDV) hepatitis C (HCV) and hepatitis G (HGV) are endemo-sporadic; they can evolve according to chronicity, with viruses staunchly persisting in carriers who constitute their principle reservoir. Viral hepatitis is a cosmopolitan disease. However its geographical distribution is not homogeneous and its impact on public health varies according to region. Poor countries are highly exposed to ail agents of viral hepatitis with numerous chronic carriers, leading to high morbidity and mortality rates. In rich countries, progress in sanitation has lowered the incidence of infection due to feco oral transmission, but has thereby also lowered natural collective immunity against hepatitis agents, prevention of risks linked to blood and mother to child transmission has been effective, ranking sexual transmission of HBV in first place; the prevalence of chronic carriers of HCV is higher than the first serological surveys led to believe and is not limited to drug addicts polytransfused and hemodialyzed patients: the means of transmission for 40% of infected individuals remains unknown. The fight against viral hepatitis must take into account this heterogeneity and available means of specific prophylaxy. Priority must be given to hepatitis B; with over 300 million carriers of he virus and from 1 to 2 million deaths per year, it is one of the largest world endemics. On the initiative of the WHO, 80 member countries have incorporated vaccination against hepatitis B in their national vaccination programs. The fight against hepatitis A and E follows unavoidable the treatment of used water and the distribution of drinking water. Vaccination against hepatitis A, at present limited to individuals at risk in developed countries, could be extended to children in regions where epidemic risk is on the rise because the age of prime infection has risen. A vaccine against hepatitis E will be available in a few years, which will allow one to foresee a prophylaxy of lethality in endemic regions, notably among young women. Hepatitis C is a challenge for the century to come, since the elaboration of a vaccine is coming up against difficult problems of antigenic variability. Serological detection of carriers of HCV before each blood or graft donation and hospital sanitation are presently the most efficient measures of prevention. Other hepatitis agents are being identified either new ones such as the GB virus of which the pathogenic role has not yet been established, or variants such as the mutants of HBV, some of which can escape immunization. Countries must not count only on vaccines to get rid of viral hepatitis, but must control the two principle mechanisms of transmission : the feco-oral means, through sanitation and development; the parenteral means, through hygiene and health education.