Phylogenetic reconstruction of HCV genotype 1b dissemination in a small city centre: the Camporeale model.

Several seroepidemiological population-based surveys carried out in Italy have shown a high prevalence of hepatitis C virus (HCV) infection. Camporeale (CP), a small Sicilian town with a 10.4% prevalence of HCV mostly genotype 1b, probably represents a specific context, since intravenous drug addiction, and sexual promiscuity are almost absent. In order to reconstruct the pattern of introduction and diffusion of HCV in this ecological niche, the NS5 genomic region of 72 HCV genotype 1 isolates (39 from CP and 33 collected throughout Sicily) was amplified and sequenced. Sequences were aligned and analyzed by BioEdit, PAUP and BEAST, and their molecular evolution compared. Thirty-eight HCV genotype 1b isolates from CP were associated in a monophyletic "transmission cluster." By applying Monte Carlo Markov simulation, it was calculated that HCV was introduced between the end of the 1940s and the beginning of the 1950s. The phylogenetic distance between the CP cluster and other Sicilian isolates confirmed its uniqueness and the local diffusion from a common ancestor. The data obtained from classic phylogenetic analysis, combined with the application of the Bayesian analysis to the study of the coalescence of phylogenetic trees, have shown that, in CP, few HCV native strains have been transmitted in a limited length of time probably through iatrogenic routes, and then have not spread further.