Increasing importance of European lineages in seeding the hepatitis C virus subtype 1a epidemic in Spain
[Background] Reducing the burden of the hepatitis C virus (HCV) requires large-scale deployment of intervention programmes, which can be informed by the dynamic pattern of HCV spread. In Spain, ongoing transmission of HCV is mostly fuelled by people who inject drugs (PWID) infected with subtype 1a (HCV1a). ; [Aim] Our aim was to map how infections spread within and between populations, which could help formulate more effective intervention programmes to halt the HCV1a epidemic in Spain. ; [Methods] Epidemiological links between HCV1a viruses from a convenience sample of 283 patients in Spain, mostly PWID, collected between 2014 and 2016, and 1,317, 1,291 and 1,009 samples collected abroad between 1989 and 2016 were reconstructed using sequences covering the NS3, NS5A and NS5B genes. To efficiently do so, fast maximum likelihood-based tree estimation was coupled to a flexible Bayesian discrete phylogeographic inference method. ; [Results] The transmission network structure of the Spanish HCV1a epidemic was shaped by continuous seeding of HCV1a into Spain, almost exclusively from North America and European countries. The latter became increasingly relevant and have dominated in recent times. Export from Spain to other countries in Europe was also strongly supported, although Spain was a net sink for European HCV1a lineages. Spatial reconstructions showed that the epidemic in Spain is diffuse, without large, dominant within-country networks. ; [Conclusion] To boost the effectiveness of local intervention efforts, concerted supra-national strategies to control HCV1a transmission are needed, with a strong focus on the most important drivers of ongoing transmission, i.e. PWID and other high-risk populations. ; Bram Vrancken is a postdoctoral research fellow funded by the Research Foundation Flanders - Fonds voor Wetenschappelijk Onderzoek Vlaanderen (FWO, Flanders, Belgium). Part of this research was sponsored by FWO grants G.0E84.16N, G.0B23.17N, G.0662.15N, G.0D51.17N and G.0B93.17N. Funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 725422-ReservoirDOCS) has been used for this study. A part of the computational resources and services used in this work were provided by the Hercules Foundation and the Flemish Government - department EWI-FWO Krediet aan Navorsers (Theys, KAN2012 1.2.249.12). This work was supported in part by grants from Fondo de Investigación Sanitaria (www.isciii.es) (PI15/00713), Plan Nacional de I+D+I and Fondo Europeo de Desarrollo Regional-FEDER (www.red.es/redes/inicio) (RD16/0025/0040), Fundación Progreso y salud, Junta de Andalucía (www.fps2.junta-andalucia.es/fundacionprogresoysalud/es/home) (PI-0411-2014), and GEHEP-SEIMC (GEHEP-004 and GEHEP-005).