Hepatitis C Virus - Evolution

Evolution

Identifying of the origin of this virus has been difficult but genotypes 1 and 4 appear to share a common origin. A Bayesian analysis suggests that the major genotypes diverged about 300–400 years ago from the ancestor virus. The minor genotypes diverged about 200 years ago from their major genotypes. All of the extant genotypes appear to have evolved from genotype 1 subtype 1b.

An study of genotype 6 strains suggests an earlier date of evolution: ∼1,100 to 1,350 years before the present (95% credible region, 600 to >2,500 years ago). The estimated rate of mutation was 1.8 × 10−4 (95% credible region 0.9 × 10−4 to 2.9 × 10−4). This genotype may be the ancestor of the other genotypes.

A study of European, USA and Japanese isolates suggested that the date of origin of genotype 1b was ~1925. The estimated dates of origin of types 2a and 3a were 1917 and 1943 respectively. The time of divergence of types 1a and 1b was estimated to be 200–300 years.

A study of genotype 1a and 1b estimated the dates of origin to be 1914-1930 (95% credible interval: 1802-1957) for type 1a and 1911-1944 (95% credible interval: 1806-1965) for type 1b. Both types 1a and 1b underwent massive expansions in their effective population size between 1940 and 1960. The expansion of HCV subtype 1b preceded that of subtype 1a by at least 16 years (95% credible interval: 15–17 years). Both types appear to have spread from the developed world to the developing world.

The genotype 2 strains from Africa can be divided into four clades that correlate with their country of origin: (1) Cameroon and Central African Republic (2) Benin, Ghana and Burkina Faso (3) Gambia, Guinea, Guinea-Bissau and Senegal (4) Madagascar.

Genotype 3 is thought to have its origin in South East Asia.

These dates from these various countries suggests that this virus may have evolved in South East Asia and was spread to West Africa by traders from Western Europe. It was later introduced into Japan once that country's self imposed isolation was lifted. Once introduced to a country its spread has been influenced by many local factors including blood transfusions, vaccination programmes, intravenous drug misuse and treatment regimes. Given the reduction in the rate of spread once screening for Hepatitis C in blood products was implemented in the 1990s it would seem that at least in recent times blood transfusion has been an important method of spreading for this virus. Additional work is required to determine the dates of evolution of the various genotypes and the timing of their spread across the globe.