| Hepatitis
C virus (HCV) exhibits significant genetic variability
throughout its entire genome. Six distinct HCV genotypes
have been identified and more than 50 subtypes. Genotypes
1a and 1b are the most common in Western Europe and
the USA, followed by genotypes 2 and 3. Genotype 4 is
found predominantly in Egypt, genotype 5 mainly in South
Africa, and genotype 6 mainly in South East Asia.
The
identification of genotype is an important factor in
the management of HCV-infected individuals, influencing
both the duration of and the sustained response to therapy.
Prior to initiating therapy, it is recommended that
all patients be genotyped. Those patients with genotype
1 should receive a 48-week course of combination therapy,
while for patients with genotypes 2 and 3, a 24-week
course of therapy is usually adequate. Additionally,
patients with genotypes 2 and 3 are almost three times
more likely to respond to therapy.
Determination of HCV genotype is frequently based on
interrogation of the highly conserved 5’ UTR region
of the HCV genome. However, it has been suggested that
this region is not heterogeneous enough to differentiate
between 1a and 1b genotypes. Use of the NS5B or core
regions has been shown to provide accurate identification
of these subtypes, and some studies have reported differences
in outcomes between patients infected with 1a vs 1b.
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