Hepatitis B and hepatitis delta virus infection in South America.

About 100,000 cases of acute hepatitis B virus (HBV) infection occur annually in South America. The overall prevalence of HBV infection in low risk populations ranges from 6.7% to 41%, while hepatitis B surface antigen (HBsAg) rates range from 0.4% to 13%. In high endemicity aboriginal or rural populations, perinatal transmission may play a major part in the spread of HBV. In urban populations, however, horizontal transmission, probably by sexual contact, is the predominant mode of spread, with higher rates of HBV positivity in lower socioeconomic groups. High risk populations such as health care workers and haemodialysis patients show higher rates of HBV infection than comparable populations elsewhere. The risk of posttransfusion hepatitis B remains high in some areas. Concomitant HBV infection may accelerate the chronic liver disease seen in decompensated hepatosplenic schistosomiasis. In the north, the prevalence of hepatitis delta virus (HDV) infection ranks among the highest in the world. In the south, the problem appears negligible although it is increasing within high risk urban communities. HDV superinfection has been the cause of large outbreaks of fulminant hepatitis. The cost of comprehensive or mass vaccination programmes remains unaffordable for most South American countries. Less expensive alternatives such as low dose intradermal schedules of immunisation have been used with success in selected adult subjects.