Could Treatment for HIV Increase the Risk of Developing Syphilis?

A recent study found that treatment with highly active antiretroviral therapy (HAART) may increase the risk for syphilis, chlamydia, and gonorrhea in individuals with HIV-1.

For their study, researchers conducted a literature search on recent syphilis cases, behavioral patterns, and biological conditions that would result in increased rates of T. Pallidum in men who have sex with men. In addition, the researchers developed a mathematical model of HIV-1 and T. pallidum co-infections in 2 risk groups with assortative mixing to explore HAART-induced changes in behavior verses HAART-induced biological effects.
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In the mathematical model, researchers explored effects on syphilis prevalence of HAART-induced changes in behavior versus immunology. “For behavioral change, we assumed that individuals on HAART adopt riskier sexual behaviors by increasing their partnership formation rates, which increases their ability to transmit T. pallidum. For immunological change, we assumed that individuals on HAART have a higher susceptibility to T. pallidum than individuals who are untreated,” the researchers wrote.

The mathematical model demonstrated that combined changes in sexual behavior and the immunological effects of HAART increased the prevalence of syphilis in men who have sex with men, compared to either factor by itself.

“The immunological effects of HAART and HAART-induced behavioral change can in principle act synergistically to increase syphilis prevalence by amounts comparable with that observed in the ongoing outbreak,” the researchers stated.

In addition, the researchers suggest that additional studies on the immunological effects of HAART in HIV-1 infected individuals should be conducted to examine the relationship between the HAART suppression of proinflammatory responses of the immune system in connection to other diseases and non-AIDS related cancers.

“Overall, these findings suggest a possible link between HAART and an increased risk for selected diseases of infectious and non-infectious origin, a potential unforeseen consequence that warrants further study,” the researchers concluded.

—Melissa Weiss

Reference:

Rekart ML, Ndifon W, Brunham RC, et al. A double-edged sword: does highly active antiretroviral therapy contribute to syphilis incidence by impairing immunity to Treponema pallidum [published online January 16, 2017]. Sexually Transmitted Infections. doi:10.1136/sextrans-2016-052870.