New research suggests that antiretroviral drugs used to treat HIV could boost the susceptibility of gay and bi men to the bacteria which causes syphilis.

According to the new research published in the journal ‘Sexually Transmitted Infections’, highly active antiretroviral therapy (HAART), could make men who have sex with men’s (MSM) susceptibility to the Treponema pallidum bacteria increase.

This research suggests that a link between the HAART and sharply rising numbers of cases of syphilis in MSM and HIV-positive men.

Recently it has appeared a mystery why numbers of cases of syphilis among MSM have risen so sharply, and have sometimes risen to proportions higher than chlamydia and gonorrhoea.

This has appeared strange to medical professionals as HAART is intended to boost the immune system activity of the subject.

The study looked at the rising numbers of syphilis infections by using risk ‘models’ with one lower risk, and one higher risk model.

Researchers assumed that those on HAART resulted in more risky sex, or increased numbers of sexual partners.

Calculations by the study suggest that either, or both factors could increase susceptibility to the bacteria that causes syphilis.

“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,” researchers write.

The research was described as “intriguing”, and researchers add: “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]. As history has shown many times over, that would be a costly mistake.”

Concluding: “Over the past 15 years, syphilis rates among [men who have sex with men] have been rising unabated. We are not aware of any recent intervention that has led to a sustained decline in [these rates] in this population.

“If further investigations support a role for [antiretroviral therapy] in increasing susceptibility to syphilis, this will provide one more reason why screening, diagnosis and treatment of [sexually transmitted infections] in [men who have sex with men] must be prioritised.”