Epidemiological and molecular aspects of hepatitis B infection in Kenya

Abstract

Kenya is one of the areas of the world with a high prevalence of hepatitis B virus infection. Although much is known about the virus, the modes of transmission in such endemic areas are not fully determined. The aim of this work was to investigate some aspects of hepatitis B virus infection including the relationship of hepatitis B to hepatocellular carcinoma and the possible means whereby infection may be prevented. For this purpose, a laboratory was established in Nairobi and personnel trained to facilitate the routine testing of sera for markers of hepatitis B infection using, in the main, an assay system based on monoclonal antibodies. Once the local availability of modern diagnostic techniques had been established, various epidemiological studies were commenced. The results showed that although perinatal infection with hepatitis B virus was uncommon, probably due to low levels of circulating hepatitis B viral DNA in the maternal plasma, infection with hepatitis B virus was frequent, commencing around 3 years and increasing linearly with age to peak around 30-40 years. Over 80% of urban Kenyan adults showed some markers of hepatitis B infection with around 8% having hepatitis B surface antigenaemia. As the vast majority of Kenyan adults have immunity to both the hepatitis A virus and the hepatitis B virus it was of interest to determine the aetiology of acute hepatitis in this group. Markers for acute hepatitis A virus, hepatitis B virus and other hepatitic viruses were examined in the sera of 94 adult patients presenting with acute hepatitis. Hepatitis B virus was responsible for 70% of cases and the hepatitis A virus for only 12%. In the majority of cases known risk factors for hepatitis B infection, including tribal scarification and circumcision, were absent. A national epidemiological survey of the prevalence of hepatitis B infection and delta virus infection was undertaken. The distribution of both hepatitis B virus and delta virus was very variable. In certain tribes of pastoral nomads the prevalence of hepatitis B surface antigenaemia was found to be over 25%, with delta antibody present in 60%. A study conducted at the Kenyatta National Hospital confirmed the close relationship of cirrhosis and hepatocellular carcinoma with the presence of hepatitis B surface antigen in the serum. A Southern blot analysis of DNA extracted from liver tissue of patients with hepatocellular carcinoma showed that integrated HBV-DNA sequences could be detected in 41% of cases and episomal HBV-DNA in 18%. This gives further support to the epidemiological evidence implicating the hepatitis B virus in the aetiology of hepatocellular carcinoma. These studies have emphasized the importance of active intervention against hepatitis B infection taking place at an early age. Unfortunately the cost of vaccination for countries like Kenya is prohibitive. An attempt was therefore made to try and lower the cost of vaccination by reducing the dosage. It was found that one-fifth of the conventional dose of vaccine given intradermally to neonates achieved a 90% seroconversion. However the antibody titres were much lower than those resulting from the administration of the conventional dose and this may adversely affect the long term protection against hepatitis B infection.