Genotypes of hepatitis C

Which genotype of hepatitis C somebody has dictates what treatment is available to them. If you are living with genotype 3, then there is evidence that liver disease might progress more quickly.

The ability of the virus to mutate has resulted in the existence of different genetic variations of HCV. These are called genotypes. The different genotypes are often, but not exclusively, related to different parts of the world.

Genotypes 1, 2 and 3 have a worldwide distribution. Types 1a and 1b are the most common, accounting for about 60% of global infections. They predominate in Northern Europe and North America and in Southern and Eastern Europe and Japan. Genotype 2 is less frequently represented than type 1. Genotype 3 is endemic in south-east Asia. Genotype 4 is principally found in the Middle East, Egypt, and central Africa. Type 5 is almost exclusively found in South Africa. The most common genotypes found in the UK are 1 and 3.

Map of the distrubution of the hepatitis C genotypes

It is still unclear whether or not the type of virus affects the progression of the disease. If it does it is not thought to present any real cause for concern. However, HCV genotype does influence response to treatment. If you are considering treatment it is very important to know which genotype (and ideally the subtype) you are actually infected with.

Each genotype also contains a series of minor variations. These are known as ‘subtypes’. They are numbered a,b,c,d etc., in order of their discovery. A person chronically infected with hepatitis C will have a viral population consisting of a very large quantity of these minor genetic variations. These are called ‘quasi species’ and present an even more complex problem for the immune system to deal with.

HCV is also described as having positive-sense, single-stranded RNA genomes. This means that each viral particle contains a single RNA strand. Within HCV the RNA has two functions. Firstly, it holds the information about HCV genetics. Secondly, it also contains information about how to make the proteins the virus needs for replication, both from its own components and from those of the host liver cell.