US investigators have detected what appear to be two cases of HIV superinfection in chronically infected gay men taking antiretroviral therapy. The cases are described in the May edition of PloSOne. Although the superinfection occurred in couples taking HIV treatment, they note that both were in couples where viral load was detectable.
Individual case reports and cohort studies show that it is possible for individuals to be infected with more than one strain of HIV. This can include co-infection, the acquisition of more than one strain of HIV at the time of initial HIV infection, and superinfection, subsequent infection with a second strain of the virus.
To gain a better understanding of the risks of superinfection, investigators from the University of Washington, Seattle, followed eight long-term gay couples where both partners were HIV-positive.
The 16 individuals included in the investigators’ analysis were enrolled in a larger study examining the association between HIV and the development of anal cancer (the Male Anal Health Study). All sixteen men had ano-genital warts.
Blood samples from the men obtained eleven and 71 months after entry into the study were analysed using a variety of techniques to see if any of the individuals had been superinfected.
Detailed sexual histories were also obtained. These indicated that during follow-up, 75% of all episodes of receptive anal sex were unprotected.
Several different tests were employed by the investigators to see if superinfection had occurred in any of the couples. These included HIV-virus isolation, PCR, cloning, sequencing, phylogenetic analysis, strain-specific PCR analysis and recombination analysis.
The men had been in relationships for between three and fifteen years. All but one had started antiretroviral therapy. Of the individuals who had started HIV treatment, only three had an undetectable viral load at each of their follow-up visits.
Viral sequencing showed that one patient had acquired two distinct strains of HIV at the time of his initial HIV infection.
The researchers’ analyses also showed that superinfection occurred in two couples. Despite taking antiretroviral therapy, viral load was detectable during follow-up in the transmitting individual. “Their antiretroviral adherence was incomplete, as evidenced by the proportion of visits with detectable viral load”, note the authors.
“Three individuals had suppression of viral replication at all visits, none of these were in couples with transmission detected during the study period”, comment the investigators. “It is reasonable to regard those who are taking antiretroviral medications as at least partially protected from acquisition of additional strains of HIV”, they add.
They also suggest a possible reason why individuals with chronic HIV have a lower risk of superinfection than those who have recently been infected with the virus. They write, “in individuals with established HIV infection, fewer host cells are vulnerable to incoming new viral strains”.
No information is provided by the investigators regarding the clinical consequences of these two cases of superinfection. Study author, Dr Mary Campbell told aidsmap: "We also could not determine whether or not superinfection had clinical implications in this group due to the relatively short follow-up period."
“These data are a reminder that precautionary measures among HIV-infected individuals are necessary”, conclude the investigators.
Campbell MS et al. HIV-1 superinfection in the antiretroviral therapy era: Are seroconcordant sexual partners at risk? PLos One 4: e5690, 2009.