Hepatitis C is a viral liver infection caused by the hepatitis C virus, or HCV. The virus demonstrates a high level of variability with several genetically distinct groups called genotypes. The World Health Organization reports that 11 major HCV genotypes exist, with many subtypes identified. Different HCV genotypes cluster in specific geographic regions. HCV genotype does not significantly affect disease course, but does influence treatment decisions.
Genotype 1
HCV genotype 1 exists throughout the world and includes two primary subtypes, 1a and 1b. The World Health Organization notes that HCV genotypes 1a and 1b cause approximately 60 percent of hepatitis C infections worldwide. In the United States, genotypes 1a and 1b account for roughly 75 percent of hepatitis C infections, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
Hepatitis C infections prove chronic in approximately 75 to 85 percent of those who contract the virus. Chronic hepatitis C often causes progressive liver scarring, which may lead to cirrhosis. Treatment with the medications pegylated interferon and ribavirin can lead to hepatitis C viral clearance in a significant number of patients, arresting the progression of HCV-induced liver damage. The required duration of treatment and potential for response varies according to the HCV genotype responsible for the infection. Overall, infections caused by genotype 1 viruses require a longer duration of treatment to induce viral clearance compared to infections caused by genotype 2 or 3. Moreover, fewer people with genotype 1 infections experience viral clearance with treatment compared to people with genotype 2 or 3.
Genotypes 2 and 3
The National Institute of Diabetes and Digestive and Kidney Diseases reports that HCV genotypes 2 and 3 account for approximately 10 to 20 percent of hepatitis C infections in the United States. Genotype 2 infections also occur in China and Japan. Genotype 3 infections are common in the United Kingdom. HCV genotypes 2 and 3 possess significant genetic differences. Nonetheless, these two HCV genotypes behave similarly with regard to response to treatment with pegylated interferon and ribavirin. The Centers for Disease Control and Prevention states that the typical duration of treatment for infections due to HCV genotype 2 or 3 is 24 weeks, compared to 48 weeks for genotype 1 infections. According to the National Institute of Diabetes and Digestive and Kidney Diseases, treatment with pegylated interferon and ribavirin leads to sustained clearance of the hepatitis C virus in approximately 70 to 80 percent of patients with genotype 2 or 3 infection, compared to 40 to 55 percent of those with genotype 1 infection.
Genotypes 4, 5 and 6
Infections with HCV genotypes 4, 5 and 6 occur uncommonly in the United States. The World Health Organization reports these genotypes most commonly occur in Africa, Asia and the Middle East. The pegylated interferon and ribavirin treatment protocol for people with HCV genotypes 4,5 and 6 typically follows that used for genotype 1, as noted by California Pacific Medical Center. Optimal treatment protocols for all HCV genotypes change as new drugs become available and research provides evidence for improving outcomes.
References
- World Health Organization: The Hepatitis C Virus
- National Institute of Diabetes and Digestive and Kidney Diseases: Chronic Hepatitis C--Current Disease Management
- California Pacific Medical Center: What is Hepatitis C Genotype?
- Centers for Disease Control and Prevention: What is the Treatment for Chronic Hepatitis C?
- Centers for Disease Control and Prevention: Hepatitis C Information for Health Professionals
