Bluma Brenner, PhD, and Mark Wainberg, PhD, of the McGill AIDS Centre in Montreal, and colleagues from several hospitals and health clinics in Canada studied HIV transmission through phylogenetic analysis—essentially, drawing the virus’s family tree. The technique follows the history of a virus as it spreads from one person to another by looking at the evolution of viral genetic material in infected individuals.
Drs. Brenner, Wainberg, and colleagues found that 49 percent of early infections formed phylogenetic clusters—very close branches on the family tree. This indicated that a large portion of HIV acquisition could be attributed to individuals transmitting the virus who were themselves in the early stages of infection, before the virus had had time to mutate much. Therefore, early infection—also known as primary infection—which represented “less than 10 percent of the total samples, disproportionately accounted for about half of subsequent transmission events.?
A high viral load associated with early HIV infection is what makes newly infected individuals so infectious, according to Drs. Brenner and Wainberg. In an editorial accompanying the article, authors Deenan Pillay, MD, of the Health Protection Agency and University College London, and Martin Fisher, MD, of the Brighton and Sussex University Hospitals, pointed out that diagnosis of HIV reduces the risk of transmission. But, they note, symptoms of primary HIV infection are non-specific. Only a small proportion of infected individuals are diagnosed in early infection, thus compounding the difficulties in preventing transmission
Source:Infectious Diseases Society of America