Over the past few years, syphilis cases have abruptly increased in several countries, mostly within populations of men who have sex with men (MSM).

In British Columbia from 2005 to 2014, syphilis cases rose 91 percent while gonorrhea increased 64 percent and chlamydia increased 40 percent. MSM were disproportionately affected by the increase. Male cases soared from 202 to 524 cases, and accounted for 95 percent of all cases in 2014.

Male syphilis cases skyrocketed 235 percent from 2005 to 2014. In comparison, gonorrhea rose 42 percent while chlamydia increased 57 percent.

More specifically, cases have been found among men who are taking highly active antiretroviral therapy (HAART) for HIV infection.

In a study published in Sexually Transmitted Infections published today (January 16), researchers from the University of British Columbia, McMaster University, and the University of Victoria hypothesized that medications used in therapeutic and preventative HAART could lower the immune system responses of patients to specific diseases, such as syphilis.

UBC clinical professor Michael Rekart stated in a news release that he had noticed a gap between syphilis and other sexually transmitted diseases such as chlamydia and gonorrhea.

While researchers and clinicians had suspected that the outbreak was the result of risky sexual behaviour, studies have shown that many men with HIV employ a variety of methods to reduce risk in sexual activity.

Using mathematical modeling to predict syphilis rates based on high-risk sexual behaviour as the sole cause, Rekart and his researchers calculated a rate of increase lower than the current rate.

The report states that while clinicians and researchers view HAART suppression of proinflammatory responses as a positive effect (as it helps to reduce the conditions resulting from infection), this reduction may increase susceptibility to infection to specific diseases, such as syphilis.

The study adds that HAART treatment has been potentially associated with a higher risk of anal cancer and other types of cancer.

While Rekart emphasized that people should continue to use HAART, the study suggests that further research is required to determine the relationship between HAART and risk for specific diseases (both infectious and non-infectious) and whether there are specific drugs in the HAART medication cocktail that have an impact upon immunity.

“HAART drugs are life-saving; syphilis is curable,” Rekart stated. “HAART drugs bring people with HIV back to a normal state of immunity, they can have a normal life, they don’t get most opportunistic infections such as tuberculosis.”