[Discovery of the hepatitis C virus].

After 15 years of unsuccessful attempts, the most frequent of non-A non-B (NANB) hepatitis viruses has recently been identified and designated HCV. It is by an original and direct molecular biology approach, leading to the cloning of nucleic acids presumed to be present in an infectious plasma, that this virus could be partially characterized. The viral genome was sequenced before the agent could be detected by serology or electron microscopy. HCV is a small RNA virus with a lipid capsid, and it might be indirectly related to the flaviviruses. A non-structural, 363 aminoacid protein, corresponding to a virus replication enzyme, is the specific component originally used for the Elisa tests, now available for the serological diagnosis of HCV infection. Serological tests have shown that HCV is the most frequent of NANB viruses, being responsible for 60 to 80 percent of post-transfusion hepatitis. Anti-HCV antibodies develop slowly: in 40 percent of the cases they appear 2 to 12 months after the transaminase peak associated with primary infection, i.e. during convalescence. Among patients with chronic hepatitis, 60 to 80 percent of presumably NANB cases are positive for anti-HCV antibodies. The same applies to cirrhotic patients with or without cancer, 40 percent of whom are HCV positive. In France, the prevalence of anti-HCV antibodies among blood donors is 0.68 percent, and from March 1, 1990 testing for HCV has become compulsory. Among the groups at risk, prevalences are 70 percent in haemophiliacs, 50 to 75 percent in drug addicts and more than 30 percent in patients under haemodialysis. Sexual transmission seems to be rare but possible; 5 percent of homosexuals are HCV antibody carrier, and this proportion is higher in those who are HIV positive. We already know that some HCV positive subjects are not infectious and that some asymptomatic blood donors carry a serologically undetected HCV; the liver of at least 10 percent of patients with chronic NANB hepatitis without anti-HCV antibodies contains the RNA of HCV detectable by molecular amplification. All this leads to the concept of HCV negative viral hepatitis. The fact that the hepatitis C virus was discovered at about the same time than interferon clearance for marketing, is an exceptional public health opportunity which should generate specific programs. It may be hoped that a preventive vaccine will be developed in a not too distant future.