HCV is an RNA virus related to the flavivirus family.  RNA viruses are genetically less stable than DNA viruses and are prone to mutate during replication.  It�s a common misconception that hepatitis C is just one virus, but in reality (as a result of mutation over hundreds of years), it�s a group of very closely related strains.  They are similar enough to be called HCV, but based on genetic differences, they can be classified into distinct groups called genotypes.

Genotypes
The most commonly used classification scheme for HCV was established by Dr. P Simmonds.  This system classifies hepatitis C into major genotypes, numbered 1, 2, 3, 4 etc.  Within the major genotype groups are more closely related strains called subtypes, these have a designated lower case letter eg. 1a, 1b, 1c etc. There are at least six major genotypes (1-6) with many subtypes.  Proposed types 7-10 and 11 may be different to genotypes 1-6 or subtypes of 1-6.

Quasispecies
As the virus continues to replicate in each person, there is the potential for quasispecies to form.  Quasispecies are very closely related mutations of the original virus they were infected with.  Over time the diversity of quasispecies increases and may affect response to treatment.

Genotypes and Disease Progression
This is still a controversial area.  Many studies have shown genotype 1, especially type 1b to be associated with more advanced liver disease, however these patients are generally older and have a longer duration of infection.  Poynard et al assessed factors associated with fibrosis progression in a large study involving 2,235 patients.  No link was found between genotype and fibrosis progression.

Genotypes and Treatment
Research has shown people with genotypes 2 or 3 have a higher sustained response rate (60-70%) to combination therapy than genotype 1 (20-30%).   However other factors such as stage of fibrosis or cirrhosis, viral load, age, gender, duration of disease and excessive alcohol consumption also influence response to therapy.

Furthermore the duration of treatment is also influenced by genotype.  Previously untreated patients with genotype 1 double their chance of a sustained response when treated for 12 months instead of 6 months.  Conversely 12 months  treatment for patients with genotypes 2 or 3 does not improve response rates over 6 months treatment.

Modes of Transmission
Genotyping can been used to study the ways hepatitis C is transmitted.  It has been used to identify the source of infection in cases of patient-to-patient transmission and is also useful in the study of other modes eg. vertical (mother to baby), sexual transmission and needle stick injury.

Genotype Testing
Genotyping is not routinely performed, although some trials require genotyping prior to therapy.  Your specialist may be able to access the test for you, but it wont be cheap.  Genotyping is covered by Medicare if you are considering treatment.

Global Genotype Distribution
Some hepatitis C genotypes are largely, (but not exclusively), associated with different parts of the world.  Genotype 4 is present in over 90% of HCV infections in central Africa and accounts for the majority of infections in the Middle East.  Genotype 5 is found in over 50% of South African infections and type 6 is mainly restricted to South East Asia.  Genotypes 1, 2 and 3 are widely distributed through western countries and the Far East.