Male HIV epidemic in London spread quickly and in clusters
Phylogenetics tree of the HIV and SIV viruses (Wikipedia)
The HIV/AIDS epidemic in London in the 1990s was spread quickly and in clusters of groups of men having sex with each other within a relatively short period of time.
Collecting cluster data in the traditional way by interviewing infected men has proved challenging, particularly when tracing the network of sexual partners. Instead phylogenetics was used to examine the level of genetic relation between the viruses obtained by different individuals.
Collecting genetic data on HIV in individual patients is a part of determining an effective treatment regimen, so the Edinburgh University scientists were able to compare the sequences of genes in HIV from over 2,000 patients, largely men who have sex with men, who attended a large HIV clinic in London between 1997 and 2003. The analyzed sequences showed 402 that very closely matched at least one other viral sequence in the group. After more extended analysis, it was found that patients whose viruses matched largely arranged into six clusters each with ten or more individuals, with additional smaller clusters outside of these.
The results indicate that the growth of the HIV epidemic in London among men who have sex with men often occurred in short, rapid episodes rather than slowly over a longer time frame. Frequently, it seems that individuals passed on the virus to others just months after becoming infected themselves. This implies that transmission of the virus in the early stages of HIV likely drove the epidemic forward considerably.
It is likely, but not yet proven, that these results apply generally to HIV infections in larger populations of men having sex with men. If this is confirmed in additional studies, then this quantitative description of HIV transmission using phylogenetics can help design future strategies to strengthen HIV prevention in this population.
Elaine Warburton www.geneticsandhealth.com
