Today a welcome guest blog by a PhD student in the lab, Aderito Monjane: this paper was presented by him in a recent lab journal club, and I thought it was interesting enough to get a wider airing.
Peter V. Markov, Jacques Pepin, Eric Frost, Sylvie Deslandes, Annie-Claude Labbe´ and Oliver G. Pybus
Journal of General Virology (2009), 90, 2086–2096
Hepatitis C virus (HCV) is an important human pathogen. There are 170 million chronically infected people worldwide, and 2-4 million new cases of infection annually. The disease manifests itself late – liver cirrhosis and hepatocellular carcinoma – and in the USA alone 9000 people die of it each year.
HCV is quite diverse. Six genotypes have been identified, and each further classified into subtypes. Some of these subtypes are geographically localized and others are globally distributed. Endemic subtypes are found in the tropics (e.g. genotype 2 and 1 are found in west Africa; genotype 4 in central Africa and the middle East), whereas ‘epidemic’ subtypes are more widely distributed.
The case for the spread, genetic diversity and origin of HCV genotype 2 is very interesting. Phylogenetic studies using sequences sampled from individuals in a) west Africa (around Gambia, Senegal), b) and slightly more to the east of these countries (around Ghana, Benin), and c) central Africa (around Cameroon and Central African Republic) revealed interesting facts.
- West Africa is the origin of HCV genotype 2 and this region has the greatest amount of viral diversity. This genetic diversity decreases as one moves further to central Africa
- Sequences from west Africa are found in regions outside of west Africa, e.g. in central Africa, Madagascar and the Caribbean island Martinique, thus reaffirming that west Africa is the origin of HCV genotype 2
- The proportion of HCV genotype 2 relative to other genotypes decreases from west to central Africa. This reaffirms that there is movement of HCV genotype 2 from west to east.
Phylogenetic and molecular clock trees showed that the oldest common ancestor to the HCV genotype 2 isolates in existence worldwide came into being in the year 1091 (actually, there is 95% confidence that it was between year 709-1228), and in 1470 the first HCV genotype 2 strains afflicting individuals in the African continent came into being.
The connection between these existing HCV genotype 2 strain, the transatlantic slave trade, and the use of mass vaccination or treatment of illnesses is interesting in that it shows the inadvertent spread of viruses globally by human activities.
Ghana was the major port for slave trade. So it is perhaps of no coincidence that HCV genotype 2 strains found in the Caribbean island Martinique (as well as most of its human population) resemble the strains found currently in the Ghana-Benin region. Movement of African troops under French colonial rule from Senegal and Mauritius during WWI has also resulted in the global spread of current epidemic HCV-2 strains. An insidious effect of mass-treatment campaigns is exemplified in the different ways HCV genotype 2 spread in Cameroon and Guinea-Bissau. In Cameroon, under French colonial rule, doctors treated European colonialists and African natives against illnesses such as syphilis and yaws using intravenous drugs, before there was any awareness of blood-borne viral transmissions. As a result, by the 60’s HCV cases were higher in Cameroon compared to Guinea-Bisau, where the Portuguese colonialists used intravenous drugs to treat the European colonialists and their immediate workers only.
In summary, this study shows that there is west to east movement of HCV genotype 2, and decreasing genetic diversity away from the origin of diversity.