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Biology and genetic heterogeneity of hepatitis C virus
J Bukh1, R H Miller, R H Purcell
1Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Insights
Hepatitis C virus (HCV) causes significant global morbidity and mortality. Its genetic diversity and quasispecies nature enable immune evasion and persistent infection, complicating treatment and vaccine development.
Area of Science:
- Virology
- Hepatology
- Immunology
Background:
- Hepatitis C virus (HCV) infection is a global health concern with varied prevalence.
- Transmission occurs parenterally, sexually, and perinatally, though risk factors are often unidentified.
- HCV infection leads to chronic hepatitis, liver cirrhosis, hepatocellular carcinoma, and associated autoimmune diseases.
Purpose of the Study:
- To summarize the global impact, transmission, pathogenesis, and genetic diversity of Hepatitis C virus.
- To highlight the implications of HCV's quasispecies nature and genetic heterogeneity.
Main Methods:
- Review of existing literature on Hepatitis C virus epidemiology, transmission, and clinical outcomes.
- Analysis of studies investigating HCV genetic diversity, quasispecies evolution, and immune evasion mechanisms.
Main Results:
- Viremia occurs early post-infection, preceding seroconversion and hepatitis.
- The majority of infected individuals develop chronic infection, with less than 20% clearing the virus.
- HCV exhibits extensive genetic heterogeneity, with distinct genotypes and subtypes, and exists as a quasispecies population within hosts.
Conclusions:
- HCV infection results in substantial worldwide morbidity and mortality.
- The quasispecies nature of HCV facilitates immune evasion and persistent infection.
- HCV's genetic diversity significantly impacts diagnosis, pathogenesis, treatment strategies, and vaccine development.
Abstract:
Hepatitis C virus (HCV) has a significant, albeit varied, presence around the world. This virus is primarily transmitted parenterally, although sexual and perinatal transmission does appear to occur. However, no risk factor for transmission could be identified in a significant proportion of infected individuals. It was found that individuals became viremic early after the primary HCV infection, whereas seroconversion and hepatitis occurred several weeks later. It was demonstrated that less than 20% of patients cleared their viremia, with the majority of patients becoming chronically infected. A significant proportion of chronically infected individuals developed chronic hepatitis and liver cirrhosis, and a strong association has been found with the development of hepatocellular carcinoma. Finally, HCV seems to be associated with autoimmune diseases and type II cryoglobulinemia. Thus, significant morbidity and mortality is caused by HCV infection worldwide. In a single infected individual the genome population of HCV has been found to comprise a quasispecies that consists of a number of identical sequences (i.e., the master sequence) and other closely related sequences. The master sequence of this quasispecies population changes during infection. In particular, it has been found that the sequence of the hypervariable region I changes rapidly in infected individuals. It is possible that the quasispecies nature of HCV constitutes a mechanism by which HCV escapes immune surveillance and establishes a persistent infection in the host. It is now well established that HCV exists as distinct genotypes among different HCV isolates. According to the currently used classification these can be divided into a number of major genetic groups (or types) and subgroups (or subtypes). The extensive genetic heterogeneity of HCV has important implications for diagnosis, pathogenesis, treatment and vaccine development.