According to Hepatitis Central, an estimated 180 million people worldwide, 4 million in the United States, are infected with hepatitis C virus. Chronic hepatitis C infection is the most common reason for liver transplantation in the United States. Once a person is diagnosed with hepatitis C, genotyping (determining the genetic sequence) is performed to determine the likelihood of success and treatment duration. Treatment remains a challenge because of patient related factors: previous relapse, nonresponse to therapy, presence of cirrhosis, obesity and older age.
According to Ready To Learn: All About Hepatitis C, hepatitis C has at least six major distinct strains, or genotypes, numbered 1 to 6, in order of discovery, and 50 variants or subtypes within genotypes designated by letters as 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 4a, 5a, and 6a, etc. These different types of hepatitis C are the result of mutations when the virus replicates.
In the United States, genotype 1 is most common. In other parts of the world, other genotypes are more common. For example, genotype 4 is the most prevalent genotype in the Middle East, including Saudi Arabia.
Genotype 1
Genotype 1 (subtypes a and b) accounts for 83% of U.S. hepatitis C cases. These subtypes also are predominant in Europe. Subtype 1b is the most common genotype in Japan.
In an article in the Annals of Internal Medicine, Dr. Nizar Zein states patients with hepatitis C genotype lb were significantly older than patients with other genotypes, because they were infected in the 1960s. According to Dr. Eugene Schiff (U of Miami), this was probably a result of experimenting with drugs.
People infected with genotype 1a or 1b have a more severe form of hepatitis and are less likely to respond to treatment than genotypes 2 or 3 and usually require longer therapy: 48 weeks versus 24 weeks for genotype 2 or 3. Less than 50% of patients with genotype 1a or 1b achieve successful treatment.
Genotypes 2 and 3
Genotype 2 accounts for 12% of U.S. hepatitis C cases. People infected with genotyope 2 have a milder form of hepatitis.
Genotype 3 accounts for 5% of U.S. hepatitis C cases and has been linked to fatty liver, which is the presence of fat in liver cells; this is due to an enzyme known to play crucial role in lipid production--fatty acid synthase, which has been found at high levels in human liver cells exposed to hepatitis C virus.
About 80% of patients infected with hepatitis C virus genotype 2 or 3 are treated successfully after receiving 24 weeks' treatment with antiviral drugs.
Genotypes 4 to 6
According to an October 2005 article in the journal Clinical Gastroenterology and Hepatology, authors MH Nguyen and EB Keeffe note that genotype 4 is found in Egypt and Africa, genotype 5 in South Africa, and genotype 6 in southeast Asia. Patients with genotype 4 tend to have a poor response to treatment. Genotype 5 appears to be an easy-to-treat virus with response rates similar to those of genotypes 2 and 3 after a 48-week course of therapy.
Genotype 6 may be intermediate in response between genotype 1 and genotype 2 or 3.
References
- "Hepatitis Central": An Updated Report on Hepatitis C Genotypes
- "Ready to Learn": All About Hepatitis C
- "Annals of Internal Medicine"; Hepatitis C Virus Genotypes in the United States: Epidemiology, Pathogenicity, and Response to Interferon Therapy: Dr. Nizar Zein, Oct 1996
- "Clinical Gastroenterology and Hepatology": Clinical Prevalence and treatment of hepatitis C virus genotypes 4, 5, and 6, MH Nguyen and EB Keeffe, Oct 2005
