Injecting drug use: A vector for the introduction of new hepatitis C virus genotypes

Abstract

Hepatitis C virus (HCV) genotypes’ monitoring allows real-time insight into the dynamic changes that occur in the global epidemiological picture of HCV infection. Intravenous drug use is currently the primary driver for HCV transmission in developed and developing countries. The distribution of HCV genotypes/subtypes differs significantly between people who inject drugs (PWID) and the general population. HCV genotypes that previously exhibited a limited geographical distribution (3a, 4) are becoming more prevalent in this high-risk group. Immigration from HCV-endemic countries and the evolving networks of HCV transmission in PWID influence HCV genotypes distribution in Europe. Social vulnerabilities (e.g., unemployment, homelessness, and limited access to social and healthcare insurances systems) are important triggers for illicit drug use, which increases the associated risks of HCV infection and the frequent emergence of less prevalent genotypes. Genotype/subtype determination bears important clinical consequences in the progression of liver disease, susceptibility to antiviral therapies and the emergence of resistance-associated variants. An estimated half of the chronically HCV-infected PWID are unaware of their infection, and only one in ten of those diagnosed enter treatment. Nevertheless, PWID exhibit high response rates to new antiviral regimens, and the level of HCV reinfection is unexpectedly low. The focus of the healthcare system must be on the early detection and treatment of infection, to avoid late presentations that are associated with high levels of viremia and liver fibrosis, which may diminish the therapeutic success rate.

Keywords: Hepatitis C, Hepatitis C virus genotypes, Intravenous drug use, People who inject drugs, Direct-acting antivirals

Core tip: Careful surveillance of circulating hepatitis C virus (HCV) genotypes/subtypes is compulsory to reconstruct the natural history of HCV epidemics and viral transmission chains in high-risk populations, such as people who inject drugs (PWIDs). Genotypes 1a and 3a predominate among PWID worldwide, but genotype 4 has been reported with increased frequency. This review analyzes the factors that underlie the different distributions of HCV genotypes in PWID relative to the general population and highlights the need for early diagnosis and care in this vulnerable group, which responds well to new antiviral therapies and exhibits unexpectedly low reinfection rates.