Viral Hepatitis

Antibody and Antigen Detection Assays Hepatitis C (HCV)

Hepatitis C virus (HCV) is an infectious disease that primarily affects the liver. It is the most serious type of hepatitis virus and can lead to cirrhosis and liver failure or cancer. It is estimated that 150–200 million people, or about 3% of the world’s population, are living with chronic HCV.

GLOBAL GEOGRAPHIC DISTRIBUTION OF HCV GENOTYPES

There are 6 major strains (genotypes) of HCV worldwide, which vary in their geographic distribution. Genotype 1 is the most common strain worldwide and it is considered to be the most aggressive, followed by genotypes 2 and 3. Genotypes 4, 5 and 6 are more regionally focused to areas such as Africa (type 4), South Africa (type 5) and Southeast Asia and China (type 6). Although HCV genotyping assays are not required to diagnose an HCV infection, it is critical information for prescribing HCV treatment since each strain responds differently to the various medications used to treat an HCV infection. Most acute hepatitis infections do not get treated as infected individuals are usually not aware they have been exposed to the virus and they do not develop any symptoms. About 85% of infections will progress to chronic hepatitis and remain undiagnosed for several decades until liver damage is detected during routine medical exams. A chronic HCV infection that is left untreated can cause serious complications including liver cirrhosis, liver cancer and liver failure.

SOURCE: Zein NN. Clin Microbiol Rev 2000; 13: 223-35

DIAGNOSIS There are two main types of diagnostic tests for HCV (1) serological assays that detect antibody or antigen to HCV and (2) molecular assays that detect, quantify, and/or characterize HCV RNA genomes within an infected patient. Since 1990, serologic-based assays have been used to screen blood donations and to diagnose an HCV infection in symptomatic patients. Molecular assays such as PCR-based tests are generally only used as confirmation or to determine the HCV genotype. Over the years, four generations of anti-HCV tests have been developed, and each generation has resulted in an improvement in the sensitivity of detecting HCV. New-generation tests are now able to detect the total nucleocapsid core antigen whose sequence is highly conserved across all HCV genotypes, allowing for the earlier detection of an HCV infection. These assays employ a cocktail of all genotype recombinant antigens derived from the core, NS3, NS4, and NS5 regions of multiple HCV genotypes and an anti-HCV core antibody with specificity for multiple genotypes.