Hepatitis C
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.
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Hepatitis C (HCV)
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. Most acute hepatitis infections do not get treated as infected individuals are usually unaware 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.
Diagnosis
There are two main types of diagnostic tests for HCV:
- serological assays that detect antibody or antigen to HCV
- 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.
HCV Core Antigen Test
Hepatitis C core antigen can be detected soon after infection, before the development of antibodies to the virus, and remains detectable throughout chronic infection. Evaluations in transfusion settings have shown that the HCV Core Ag assay detects HCV infection as effectively as NAT, about 40-50 days earlier than the current third generation anti-HCV screening assays. HCV core antigen levels closely follow HCV RNA dynamics, and allow clinical monitoring of a patient’s therapy, independently of HCV genotype.
HCV Antibody Test
The HCV antibody test is commonly used to screen individuals with risk factors, people who have symptoms associated with hepatitis or liver disease, or those who have been exposed to the virus. It is generally followed by a confirmatory nucleic acid test to detect HCV RNA, which indicates an active viral infection. The confirmatory test is essential because between 15 and 50% of people with HCV antibodies will have spontaneously cleared HCV infection during the first six months after exposure and do not have chronic infection. Anti-HCV persists indefinitely in patients who develop chronic infection, although antibodies may become undetectable in hemodialysis patients or in cases of profound immunosuppression.
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