One is a swinger and one uses Craigslist for anonymous sexual partners.

Both have syphilis and the Middlesex-London Health Unit is warning people who may have had contact with them, or engage in similar activities, to get tested.

“We’ve recently become aware of these cases and that there may be a number of people who are engaging in the kind of high-risk activities that carry a heightened risk for the transmission of STIs (sexually transmitted infection) like syphilis and HIV,” Shaya Dhinsa, sexual health manager at the health unit, said in a release.

“Because these infections may not be accompanied by symptoms, it is possible those who participate in these activities may already be infected, and therefore could be unknowingly spreading an infection to others.

“It’s important they see their family physician or come to the health unit for testing.”

One of the individuals also has an HIV infection, the unit said.

Because one meets people through local swinger events and one meets anonymous partners through Craigslist, the health unit has been unable to contact people who might have been exposed.

Syphilis bacteria can be passed on during any form of ­sexual intercourse, such as vaginal,

oral or anal sex, and even through deep kissing, the health unit said.

It can also be spread by other means, such as sharing needles or other drug equipment.

Symptoms of syphilis can range from sores and rashes to serious internal organ damage.

The disease is easily treated with antibiotics.

Anyone who has participated in swingers’ events, or had anonymous sexual encounters with people they’ve met on social media sites such as Craigslist, Tinder or Grindr should make arrangements to be tested for STIs, including syphilis and HIV, the health unit said.

Testing is available at the health unit’s sexual health clinic located at 50 King St., on Mondays and Wednesdays from 4:30 to 7 p.m. and Friday from 8:30 to 10:30 a.m.