Does hepatitis C virus (HCV) subtype have clinical importance?
According to a recent review published in Medscape
Gastroenterology, the identification of viral subtypes is of
clinical importance because it can be predictive of response to
therapy. Many of the clinical trials that have investigated
interferon treatment of chronic hepatitis C infection have
demonstrated the effect of HCV genotype on response to therapy.
Genotype 1b is not effectively treated with interferon monotherapy,
with only 10%-15% of treated patients exhibiting long-term
response. By contrast, individuals infected with HCV of genotypes
1a, 2a, 2b, and 3a have significantly higher long-term response
rates. Additionally, the identification of subtypes is of clinical
importance, because it has been demonstrated that subtype
1a-infected individuals respond better to interferon monotherapy
than their 1b-infected counterparts.
There are 6 main genotypes of HCV, which are classified
numerically from 1 to 6. Each genotype is further stratified by
subtype, which is alphabetically assigned as "a," "b," and so on.
Molecular characterization of the virus has revealed heterogeneity
between isolates from different genotypes and individual subtypes.
The prevalence of individual genotypes varies by geographic region,
with genotype 1 showing a worldwide distribution. Other HCV
isolates are region specific.
This effect of HCV viral genotype and subtype on response to
therapy was observed to be independent of age, gender, and duration
of disease. Large clinical trials conducted by both McHutchison and
colleagues and Poynard and associates demonstrated an efficacy rate
of 65% for combination therapy in non-1b-infected individuals. The
percentage of sustained responders for genotype 1b-infected
individuals was almost twice as great with combination therapy as
with interferon monotherapy. These findings represent considerable
improvements in the treatment options for both clinicians and
patients.
Further advances in understanding the dynamics of viral
replication, the evolution of treatment-resistant quasispecies, and
how these events are likely to affect antiviral strategies will aid
in the development of novel therapeutic approaches.
Source: Fanning LJ, Shanahan F.: The Hepatitis C Virus:
Master of Diversity and Challenging Adversary. Medscape
Gastroenterology, 2000. © 2000 Medscape, Inc.
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