According to the World Health Organization, approximately 150 million people in the world are chronically infected with hepatitis C virus (HCV), and every year more than 350 thousand people die of hepatitis C-related liver diseases. HCV affects mainly liver. The disease may be either acute or chronic, and it often presents itself without symptoms. However, the chronic infection could lead to liver cirrhosis and development of hepatocellular carcinoma.
HCV is a small coated virus (50 nm in diameter) which belongs to family Flaviviridae containing single-stranded RNA. HCV genome has areas encoding structural and nonstructural proteins. The structural antigens are nucleocapsid protein (core protein) and two outer shell proteins E1 and E2. Nonstructural proteins are proteins with enzymatic activity: NS2, NS3, NS4a, NS4b, NS5a and NS5b. In response to virus infection, specific antibodies to all viral proteins are produced in the human organism.
Modern laboratory diagnostics of hepatitis C is based on the identification of specific markers of HCV infection, which are: virus antigens, antibodies to viral proteins and RNA. Enzyme linked immunosorbent assay (ELISA) is the most popular method for primary diagnostics of hepatitis C in blood testing. Additionally, the detection of antibodies to HCV is informative for differential diagnostics of acute and chronic hepatitis C and for monitoring of the effectiveness of antiviral therapy.
Viral RNA is the earliest marker of HCV infection, and it is detected in the blood of an infected person within 2-6 weeks after infection. 1-2 weeks later core antigen is detected in the blood. IgM antibodies are produced 6-8 weeks after infection. These antibodies can be detected for a long time both during acute and chronic hepatitis C, and are the markers of active viral replication. During acute hepatitis C, IgM specific antibodies are found in the majority of patients. Low levels of anti-HCV IgM antibodies are found in 50-80% of cases of chronic hepatitis C, and there is a correlation between the levels of anti-HCV IgM and the presence of biochemical markers of liver disease.
IgG antibodies to proteins core (C22) and NS3 (C33) are detected early in the course of the disease, whereas, anti-NS4 antibodies are detectable much later (20-22 weeks after infection). Additionally, the intensity of production of anti-NS4 antibodies is genotype-dependent whereas levels of antibodies to core and NS3 proteins are high irrespectively of HCV genotype.
To date, in the majority of tests used for screening of donated blood, the recombinant proteins representing viral core, NS3, NS4, and NS5 proteins are being used.
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