Social Networks Shape the Transmission Dynamics of Hepatitis C Virus

Camila Malta Romano,João Renato Rebello Pinho,Marco Motoki,Paolo Marinho De Andrade Zanotto,Leda F Jamal,Fernando Lucas De Melo,Atila Iamarino,Edward C Holmes,Isabel M V Guedes De Carvalho-Mello,Bradley S Schneider

doi:10.1371/journal.pone.0011170

Camila Malta Romano, João Renato Rebello Pinho + Show 8 more

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https://doi.org/10.1371/journal.pone.0011170

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Abstract

Hepatitis C virus (HCV) infects 170 million people worldwide, and is a major public health problem in Brazil, where over 1% of the population may be infected and where multiple viral genotypes co-circulate. Chronically infected individuals are both the source of transmission to others and are at risk for HCV-related diseases, such as liver cancer and cirrhosis. Before the adoption of anti-HCV control measures in blood banks, this virus was mainly transmitted via blood transfusion. Today, needle sharing among injecting drug users is the most common form of HCV transmission. Of particular importance is that HCV prevalence is growing in non-risk groups. Since there is no vaccine against HCV, it is important to determine the factors that control viral transmission in order to develop more efficient control measures. However, despite the health costs associated with HCV, the factors that determine the spread of virus at the epidemiological scale are often poorly understood. Here, we sequenced partial NS5b gene sequences sampled from blood samples collected from 591 patients in São Paulo state, Brazil. We show that different viral genotypes entered São Paulo at different times, grew at different rates, and are associated with different age groups and risk behaviors. In particular, subtype 1b is older and grew more slowly than subtypes 1a and 3a, and is associated with multiple age classes. In contrast, subtypes 1a and 3b are associated with younger people infected more recently, possibly with higher rates of sexual transmission. The transmission dynamics of HCV in São Paulo therefore vary by subtype and are determined by a combination of age, risk exposure and underlying social network. We conclude that social factors may play a key role in determining the rate and pattern of HCV spread, and should influence future intervention policies.

Highlights

Hepatitis C virus (HCV) is a major cause of hepatitis and liver cancer globally, chronically infecting nearly 3% of the world’s population [1]
HCV epidemiology and phylogeography A total of 591 HCV sequences obtained from Sao Paulo State were successfully amplified, sequenced and typed by phylogenetic analysis using reference sequences obtained from the Los Alamos HCV database
Our study reveals that co-existing yet distinct epidemics of different HCV subtypes circulate in Sao Paulo and among discrete age-structured groups that are differently exposed to risk factors for viral transmission

Summary

Introduction

Hepatitis C virus (HCV) is a major cause of hepatitis and liver cancer globally, chronically infecting nearly 3% of the world’s population [1]. Needle sharing among injecting drug users (IDUs) is a major risk factor in industrialized countries [2] and prevalence among IDUs ranges from 30 to 90% [3,4], with between 5.6 to 36% of Brazilian drug users infected [5]. 15–40% of infected persons clear the virus during the acute phase. Nearly 80% result in chronic infections which may lead to subsequent viral transmission [6]. It has been estimated that 0.8% to 3.5% of the Brazilian population is HCV-positive, while prevalence among those that are HIV infected may reach 25% [7]

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