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 the person was 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 (approximately 80%) to combination therapy than genotype 1 (approximately 50%). 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 of treatment for patients with genotypes 2 or 3 does not improve response rates over just 6 months of treatment.
Already having Hepatitis C doesn’t protect you from reinfection. You can become infected with different strains and experience another acute stage of infection. Similarly, if you have had hepatitis C and cleared the virus, you are not immune.
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 such as vertical transmission (mother to baby), sexual transmission, and needle-stick injuries.
Genotyping is routinely performed prior to therapy. Genotype testing 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. Genotype 6 is mainly restricted to South East Asia. Genotypes 1, 2 and 3 are widely distributed through western countries and the Far East.
Australian Genotype Distribution
Several studies have been performed to determine the genotype distribution in Australia, all with similar results. At Westmead Hospital, the study ‘Molecular Epidemiology of Hepatitis C in Australia’ involved 420 patients, and showed the most common genotypes present in this group were:
Genotype 1 (52%) 219 patients
Genotype 3 (32%) 132 patients
Less common genotypes were:
Genotype 2 (9.3%) 39 patients
Genotype 4 (5.5%) 23 patients
Genotype 6 (1.7%) 7 patients
The study also aimed to determine other factors associated with the particular genotypes found. It discovered that 93% of Australian- or NZ-born patients had genotype 1 or genotype 3. Patients with genotype 1 were more likely to be older with a longer duration of disease. Of the 53 Asian-born patients, genotypes 1b (49%) and 2 (21%) were the most common, and all seven of the patients with genotype 6 were born in Asia (six in Vietnam, and one in China). Half of the Mediterranean-born patients had 1b (52%), and 33% had genotype 2. All but 2 of the patients with genotype 4 were born in the Middle East—one was born in Italy, while the other had a blood transfusion in Egypt.
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