Researchers from London have found that three percent of HIV infections acquired through sex between men between 2000 and 2005 were non-B HIV strains. However, their data, presented to the Twelfth Annual Conference of the British HIV Association (BHIVA) in Brighton on March 30th, suggest that rates of non-B HIV acquisition between United Kingdom-born gay men do not appear to be increasing.
Subtype B is the most prevalent HIV subtype found in the UK, and until recently it was the only strain of HIV infecting UK-born gay men. However, patterns of migration to the UK have led to an increase in the UK prevalence of non-B subtypes in recent years.
Researchers at a south London HIV clinic were the first to provide evidence that non-B clades (or strains) of HIV are being transmitted in the UK. In addition to finding that non-B strains are being transmitted within and between UK and non-UK born heterosexuals they found that 13 (11%) of 117 of their UK-born gay male patients were infected with non-B subtypes, of whom nine probably acquired their infection in the UK, all but two from UK-born partners. However, although these data were only published in January 2006, their study period was between May 1999 and May 2000.
Dr Julie Fox and her colleagues from Imperial College London, undertook a prospective longitudinal study of recent seroconverters at a London HIV clinic between 2000 and 2005, enrolling 135 UK-born gay men with documented evidence of having acquired HIV in the preceding six months. The men self-completed a sexual behaviour questionnaire, and their HIV underwent detailed genetic analysis.
A total of five (3%) out of the 135 men in the study were identified as having non-B HIV strains. All of the men's sexual contacts were thought to be exclusively gay and no-one reported sex with an individual from a country where non-B subtypes are predominant.
However, the researchers found that there was no change in the frequency of non-B acquisition over time.
"Interestingly," reported Dr Fox, "all of the non-B subtypes were recombinant strains, and only two contained a B-clade component. It is unusual to see these patterns of recombination in either heterosexual or homosexual populations."
A total of four different recombinant strains were identified. The two men with A/E+D had been sexual partners, with the second infection occurring a year after the first. The other recombinant strains were C+B, D+B, and CRF02-AG+K.
She suggested that the unusual patterns of recombination may mean that the men were either dually- or superinfected. Evidence suggests that individuals who are recently infected are more likely to be superinfected.
In addition, all of the non-B strains were wild-type with no evidence of drug resistance.
In contrast, a presentation from the Royal Free Hospital in north London found that eleven out of 100 (11%) gay men newly diagnosed (but not necessarily recently infected) with subtype B HIV between April 2004 and November 2005 acquired drug-resistant strains.
The same presentation reported that five of the newly diagnosed gay men from white European backgrounds were infected with non-B HIV strains. Three of the men had the same circulating recombinant form, CRF06.
Dr Fox said that studies are ongoing to further examine how the men became infected with these recombinant strains, and whether non-B HIV infection leads to slower disease progression.
She concluded by stating that, "this study provides evidence that, with time, the traditional segregation of clades [seen in the UK] is becoming less visible," and that these data will have an impact on vaccine development, since "in time all vaccines will need to target all clades in order to have a significant impact on the epidemic."
Fox J et al. Incident non-B clade HIV-1 infection in white gay men infected in UK between 2000 and 2005. HIV Med 7 (supplement 1), abstract 03, 2006.
Garcia A et al. The demographic, clinical and virological characteristics of patients newly diagnosed with non-B HIV-1 subtypes in London. HIV Med 7 (supplement 1), abstract 02, 2006.