[Limits of immunoserologic and molecular diagnosis of hepatitis C].
Hepatitis C is the most common cause of post-transfusion hepatitis, as well as of the viral chronic liver disease in the western world. However since it is even more often asymptomatic than HBV, this is not truly recognized. The detection of hepatitis C can only rely on serological and virological methods and require their extensive use in screening programs. Following the molecular identification characterisation of HCV, it became possible to detect virus specific antibodies. The first generation Elisas were limited in their scope and have been replaced by second and third generation tests with better sensitivity and specificity. These assays detect antibodies to several sets of HCV protein including the C22 core, the C33 and C100, which correspond to the non structural regions (NS3 and NS4 respectively). More recently, NS5 proteins have also been added and synthetic peptides have replaced some of the recombinant proteins used initially. In spite of improved sensitivity and specificity, last generation Elisas still require confirmation by supplemental assays which can be of different types (immunoblot or combined Elisas) and include sets of structural and non structural recombinant proteins or peptides. New tests are needed to improve sensitivity and proficiency of this mandatory confirmation procedure. It is unclear at this stage whether the dogma inherited from HIV to request two sets of reactive antibodies will be also warranted by experience in HCV infection. The biggest limitation of present HCV tests is the delayed appearance of anti-HCV following primary infection. Even more worrisome is the fact that 10% of chronic infection with liver disease still remain seronegative, despite circulating HCV RNA in serum and/or liver as well as expressing HCV antigen demonstrable in liver tissue by immunostaining. Such a proportion is even more common in settings with immune deficiencies including organ transplantation and HIV infection. DNA amplification methods, such as PCR or others, must be used in order to demonstrate HCV RNA in combination with reverse transcription steps. This new powerful technology must be however applied under stringent quality control procedures and cannot be yet considered for screening or routine diagnosis although it can detect viremia as early as a week after exposure and help to monitor interferon treatment. During acute hepatitis, the delay in the appearance of anti-HCV hampers acute phase diagnosis. The early detection of HCV RNA in peripheral blood, confirms the diagnosis and opens up therapeutic possibilities. In chronic hepatitis, the diagnosis of seronegative forms may only be resolved by PCR. Moreover, the presence of HCV RNA in peripheral blood represents the only marker of on going viral replication and coincides with the severity of liver damage. During treatment with interferon, the follow up of HCV RNA sequences makes it possible to monitor its efficacy. The search for HCV RNA sequences directly in liver tissue shows that HCV may replicate in the liver in the absence of viremia. The presence of HCV RNA in the liver and the serum of liver transplanted patients is essential for the etiological diagnosis and management of hepatitis and bone marrow failure occurring after transplantation. Epidemiological study using PCR is a major tool in documenting vertical transmission between mother and child. Finally, PCR is important for the analysis of the HCV genome. Thus, in France there are at least three main strains, one close to the US prototype, the other close to the Japanese strain, possibly responsible for a more severe illness, and a third one distinct from the previous two. Two major HCV genotypes, F1 and F2, corresponding to HCV type I and II (USA prototype and Japanese) with prevalence of 45% and 55% respectively, were found in France. F1 infected patients were younger and more often male than F2 group. Nine of 28 patients in F1 genotype infected group had history of drug abuse but none i