What's new in hepatitis delta virus?

Seven years of clinical and laboratory research have provided us with a rather good knowledge of the infectious agent that causes hepatitis delta. This agent is a small RNA containing virus (hepatitis delta virus), which is functionally incomplete and needs the help of hepatitis B virus for infection and replication. It is unique also in respect to its RNA, which is smaller than the RNA of every other known RNA virus, but larger than the RNA of the viroids of higher plants. Animal experiments as well as clinical studies showed that hepatitis delta virus infection can be transmitted either simultaneously with hepatitis B, leading to a clinical picture which usually resembles that of hepatitis B alone, or as superinfection of a chronic HBsAg-carrier. The latter often leads to severe, and sometimes fatal, acute hepatitis, followed by chronic liver disease in as many as 30-40% of cases. The hepatitis delta virus is distributed world-wide, showing a high endemicity in Italy and some Arab countries, but also in certain risk groups such as intravenous drug addicts and haemophilics. Further epidemiological studies will probably reveal other foci where the hepatitis delta virus is endemic; especially in Africa, areas of high endemicity of hepatitis delta virus are suspected. Extensive research on delta agent is continuing: further clinical studies, using the highly sensitive method of DNA-RNA-hybridization for the detection of hepatitis delta virus RNA, will tell us more about the role of this virus in acute and chronic hepatitis, and future biochemical and biological research may be expected to increase our insight into the still enigmatic cooperation of the hepatitis delta virus and hepatitis B viruses.