A genotype is a classification of a virus based on the genetic material in the RNA strands of the virus. There are six distinct genotypes of hepatitis C virus in the world with multiple sub-types in each genotype class. The reason chronic hepatitis C is so difficult to treat is because of these multiple distinct genotypes. A patient is usually only infected with one genotype, but each genotype is actually a mixture of closely related viruses called quasi species. These quasi species have the ability to mutate very quickly and become immune to current treatments.
The following table lists the different genotypes of chronic hepatitis C virus and where they are found in the world:
Genotype 2a, 2b, 2c & 2d
Genotype 3a, 3b, 3c, 3d, 3e & 3f
Genotype 4a, 4b, 4c, 4d, 4e, 4f,
4g, 4h, 4i & 4j
Although the table lists the areas of the world where the different genotypes are prevalent, it is possible to have any of the genotypes without actually visiting that country. Blood products can come from any part of the world and before 1991 hepatitis C blood donor screening was not performed. The HCV antibody tests were not developed or put into practice until 1991.
Treatment Response Statistics:
Current data and studies have shown that certain genotypes respond to treatment better than others. Doctors do not decide which patients will be treated based on the genotype they have because some of each genotype will respond to treatment.
HCV genotyping is performed by line probe assay or direct sequencing. Pretreatment HCV genotyping is essential for determining likelihood of treatment response. Patients infected with HCV genotypes 2 and 3 respond more favorably to therapy, with 70% to 80% sustained viral response (SVR) rates, whereas those with genotype 1 (75% of patients infected with HCV in the United States) have an SVR rate of 42% to 51%. Furthermore, treatment for genotypes 2 and 3 can be limited to 24 weeks. Genotype 1 always requires treatment for 48 weeks.
The following table gives some of the statistics of sustained response to treatment with PEG-Intron (Pegylated Interferon alfa 2b) and Ribavirin combination vs genotype:
Dose used for data in the following table: PEG-Intron(Pegylated Interferon alfa 2b) 1.5 ug/kg/wk and Rebetol 800mg/day x 48 weeks
Treatment for Hepatitis C is sometimes relegated to taking the herbal supplement Milk Thistle.