It is much easier to talk of the hepatitis C virus as
if it is a single organism but in fact it is a range of viruses,
similar enough to be called hepatitis C virus, yet different enough
to be classified into subgroups. Viruses are microscopic and no
person could ever see them with the naked eye. Indeed, HCV is so
small that there’s been no confirmed actual sighting of it
using any type of microscope yet developed (see Ed 17, p1).
Consequently, a better way to understand the terms HCV
‘genotypes’ and ‘subtypes’ is to compare
them to things that we can more readily relate to.
The group of birds we call ‘raptors’ (birds of prey)
have evolved into different main types. Imagining raptors as being
hepatitis C viruses, you could take one major raptor type, such as
eagles, and imagine these as being one of HCV’s main types
But eagles as a group are made up of different sub types such as
the American Bald Eagle and Australia’s Wedge Tailed Eagle
and Sea Eagle. You could imagine each of these as being one of the
HCV subtypes that make up an HCV genotype.
Within each of above particular types of eagles, there are further
differences. All Wedge Tailed Eagles, for example, differ from each
other in regard to wing span, weight, colour, beak size, etc.
Similarly, within a hepatitis C sub-type, individual viruses differ
from each other ever so slightly. Such viral differences are not
significant enough to form another sub-type but instead form
what’s known as quasi-species. It is believed that within an
HCV sub-type, several million quasispecies may exist.
Scientists predict that people who have hepatitis C, have billions
of actual viruses circulating within their body. Although there may
be one or two predominant sub-types, the infection as a whole is
not a single entity and is composed of many different
Biologists are generally not known for creativity when it comes to
naming things - hence hepatitis C virus. The most commonly used
classification of hepatitis C virus has HCV divided into the
following genotypes (main types):
1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11.
As we’ve highlighted, HCV genotypes can be broken down into
sub-types, some of which include:
1a, 1b, 1c
2a, 2b, 2c
4a, 4b, 4c, 4d, 4e
It is believed that the hepatitis C virus has evolved over a period
of several thousand years (see Ed 20, p7). This would explain the
current general global patterns of genotypes and subtypes:
1a - mostly found in Nth & Sth America; also common in Australia
1b - mostly found in Europe and Asia.
2a - is the most common genotype 2 in Japan and China.
2b - is the most common genotype 2 in the US and Nthn Europe.
2c - the most common genotype 2 in Wstn and Sthn Europe.
3a - highly prevalent here in Australia (40% of cases) and Sth Asia.
4a - highly prevalent in Egypt
4c - highly prevalent in Central Africa
5a - highly prevalent only in Sth Africa
6a - restricted to Hong Kong, Macau and Vietnam
7a and 7b - common in Thailand
8a, 8b & 9a - prevalent in Vietnam
10a & 11a - found in Indonesia
It’s believed that of the estimated 160,000 Australians
with HCV, approx. 35% have subtype ‘1a’, 15% have
‘1b’, 7% have ‘2’, 35% have ‘3’
(mostly being 3a). The remaining people would have other
Genotype and treatment
Current scientific belief is that factors such as duration of a
person’s HCV infection, their HCV viral load, age, grade of
liver inflammation or stage of fibrosis may play an important role
in determining response to interferon treatment. Recent studies
have suggested that a person’s HCV subtype (or subtypes) may
influence their possible response to interferon, or
interferon-ribavirin combination treatment. World-wide trials are
being conducted which will soon shed more light on this belief.
We’ll publish any reports as they come to hand.
Info taken from Genotypes and Genetic Variation of Hepatitis
C Virus by G. Maerterns & L. Stuyver, reviewed by Dr Greg Dore
of the National Centre in HIV Epidemiology & Clinical
From The Hep C Review; Ed 23, December 1998; Paul Harvey
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