Doctors in Halifax are treating a rising number of syphilis cases, mostly among men.

Cases of the sexually transmitted infection have spiked since 2008, when it was virtually unknown in the city.

Since January, that pace has accelerated, said Dr. Todd Hatchette, a specialist in infectious diseases at the QEII Health Sciences Centre.

"Last year, we saw probably 18 cases, so we've seen as many cases in the first six months of this year as we did all of last year," he told CBC News.

Syphilis is transmitted through oral, genital or anal sex with someone already infected with it. Symptoms include hair loss, a rash, swollen glands, and muscle and joint pain, but they can disappear on their own and the infection remains.

Syphilis can be cured with antibiotics. If untreated, though, it can affect the brain, blood vessels and heart, and ultimately lead to death.

The resurgence of syphilis in Halifax follows a national trend.

In 2001, there were 300 cases in Canada. The numbers have been rising ever since, with outbreaks in Alberta and New Brunswick. In 2009 — the most recent numbers available — there were more than 1,600 cases across Canada.

Hatchette said a decline in condom use contributes to the pattern, along with the mistaken belief that oral sex is safe.

He said so far in Nova Scotia, every case involves men having sex with men, but he expects that to change.

"Some of the men who tested positive have had both male and female partners, so it would not be surprising that at some point we see this infection transmitted between men and women on a more regular basis," he said.

Maria MacIntosh, with the AIDS Coalition of Nova Scotia, encourages people who suspect they have syphilis to find out for sure.

"The best thing one can do is to consider going out and getting the test just to know what your situation is," she said.

MacIntosh and Hatchette believe the Nova Scotia outbreak can be contained through more testing and treatment.