Short communicationVariable epidemic histories of hepatitis C virus genotype 2 infection in West Africa and Cameroon
Introduction
Hepatitis C virus (HCV) infection is a major public health problem worldwide. The World Health Organization (WHO) estimates that about 3% of the world's population (nearly 170 million people) is chronically infected with HCV (WHO, 1999). Africa is reported to have the highest regional HCV prevalence rate (5.3%) (Madhava et al., 2002). HCV is a highly genetically variable virus that has been classified into six phylogenetically distinct genotypes, each containing multiple subtypes (Simmonds et al., 2005). There are marked differences in the distributions of the genotypes and subtypes worldwide; some of them are distributed globally, whereas others are found only in specific geographic regions. Genotypes 1, 2, and 4 appear to be endemic to regions of West and Middle Africa and the Middle East, whereas divergent endemic strains of genotypes 3 and 6 are found in Southeast Asia (McOmish et al., 1994). It is not yet clear where the region of endemic infection for genotype 5 is located (Verbeeck et al., 2006).
Advances in the evolutionary analysis of sampled viral gene sequences have enabled the reconstruction of the past virus transmission trends from contemporary infections (Drummond et al., 2005, Nakano et al., 2004, Pybus et al., 2001, Pybus et al., 2003, Tanaka et al., 2002, Tanaka et al., 2004). Recently, a Bayesian coalescent approach (Drummond et al., 2005) was used to estimate the dates of origin and the rates of virus spread through time for HCV genotypes 1, 2 and 4 found in Cameroon and Middle Africa (Njouom et al., 2007). By comparing the dates of the most recent common ancestors (MRCAs) of these strains, the authors suggested an endemic origin for HCV genotypes 1 and 4 infections and, most probably, a more recent introduction of genotype 2 (HCV-2) into Cameroon. Previous phylogenetic studies have reported great genetic diversity of HCV genotype 2 in West African countries, associated with a high virus prevalence (Candotti et al., 2003, Jeannel et al., 1998, Ruggieri et al., 1996, Wansbrough-Jones et al., 1998), suggesting that this genotype has been present in the human population of this part of Africa for some time.
Here, Cameroonian genotype 2 strains were analysed in conjunction with genotype 2 strains from West African countries. A phylogenetic analysis was used to explore the link between HCV2 strains in Cameroon and West Africa. Furthermore, a Bayesian coalescent approach was used to estimate the age of strains from both locations, and to estimate the historical rates at which these strains spread through populations. By shedding light on the history of HCV transmission, these results can inform HCV control initiatives and help to understand the future burden of HCV-related disease in Africa.
Section snippets
Materials and methods
Two HCV-2 datasets of partial NS5B gene sequences were used in this study. The first dataset contains 58 sequences, 382 or 405 bp long, from HCV-infected patients from Cameroon (Ndjomou et al., 2003, Njouom et al., 2003, Njouom et al., 2005, Pasquier et al., 2005). The second dataset was comprised of 40 sequences, 200, 270 or 340 bp long, from HCV-infected patients residing in four different West African countries (Fig. 1A) (Candotti et al., 2003, Jeannel et al., 1998, Ruggieri et al., 1996). No
Results and discussion
The model with the smallest AIC score was the GTR model with gamma-distributed rate variation plus invariant sites (Table 2). Consequently, this model was used in the rest of the study (phylogenetic and BEAST analyses). Fig. 1B shows the estimated phylogeny of the HCV NS5B sequences from Cameroon and West African countries. One sequence from Ghana (GH07-CA, referred in the original article as G4720, Candotti et al., 2003) was highly divergent and grouped with the outgroup strains. It has been
Acknowledgements
We thank all the scientists who provided free all the software used in this study. This work was supported by the “Centre Pasteur du Cameroun”.
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