HIV treatment may up susceptibility to syphilis

Gay/bisexual men who take antiretroviral drugs, to treat HIV infection, might inadvertently be boosting their susceptibility to the bacteria responsible for syphilis, a study has found.

The findings showed that the availability of highly active antiretroviral therapy (HAART) has eliminated the fear factor, which conversely prompted higher rates of sexually transmitted infections because of risky, unprotected sex.

This may explain the reason behind the rapidly increase in the rates of syphilis in gay and bisexual men over the past decade, the researchers said.
"We are living in an era where [antiretroviral therapy] is being used to effectively treat and prevent HIV infection.

To some extent this seems to have tempered the urgency to control other [sexually transmitted infections]," said Michael.L. Rekart from University of British Columbia, in Vancouver, Canada. But, the researchers are not clear why rates of syphilis among gay/bisexual men should be so much higher than those of other sexually transmitted infections such as chlamydia or gonorrhea.

This is because HAART is known to boost immune system activity and is expected to lower susceptibility to infections. For the study, the team reviewed the impact of HAART on behavioural and immune system change.

They developed two risk models: the lower risk model compared HAART with no treatment in an HIV positive partner, while the higher risk model compared existing infection with no infection in a partner who was either HIV negative or positive.

Behaviour change meant that HAART would result in more sexual partners whereas immune system changes meant that HAART would boost susceptibility to Treponema pallidum - syphilis causing bacteria.

The results showed that either factor could produce outbreaks of syphilis, but when combined they spiraled the number of infections, suggesting an interplay between behavioural change and immune system changes.

"The study 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," Rekart noted.