Syphilis

Syphilis is a sexually transmitted infection (STI) caused by a bacterium called Treponema pallidum.

Of the “big three” common bacterial STIs, syphilis can cause the most permanent harm if left untreated, and can be fatal.

In Canada, syphilis cases have been rising a lot. Also, congenital syphilis (when it’s passed from a pregnant person to their baby) is increasing.

Why Syphilis Matters for HIV & Other STIs

• Syphilis can cause sores or damage that make it easier to get or pass HIV.
  
• You can get syphilis again even after successful treatment.
  
• Early stages often have mild or no symptoms, making it hard to know you have it.
  

Symptoms — What to Watch For

Syphilis has different stages. The signs vary by stage, and sometimes there are none at all:

• Primary stage: A single sore (called a chancre) appears where the bacteria entered (genitals, anus, throat, etc.). It’s often painless, so many people miss it.
  
• Secondary stage (weeks later): You may see a rash (sometimes on the palms or soles), flu-like signs (fever, fatigue, headache), swollen glands, or moist wart-like bumps.
  
• Latent (hidden) stage: No visible symptoms for months or years. In early latent, you can still transmit the infection.
  
• Tertiary / late stage (if untreated): Can damage heart, brain, nerves, eyes, and organs. Neurosyphilis (infection of the nervous system) can occur.
  

Because it can hide, testing is very important.

How It Spreads

Syphilis spreads through contact with a syphilis sore or rash during vaginal, anal, or oral sex. It can also spread through sharing sex toys (if sores or fluids are present). In pregnancy, it can pass from a pregnant person to the fetus.

It does not spread through casual contact like touching, toilet seats, or sharing dishes.

Getting Tested — How Do You Know?

Because syphilis can be hidden, testing is your best tool:

• Blood tests (serology) are the usual method.
  
• If there is a sore, a swab from that lesion can help detect the bacteria.
  
• After treatment, follow-up blood tests are needed to show the infection has cleared.
  
• In pregnancy, early and repeated screening is vital to prevent passing it to the baby.
  

Testing algorithms (how labs interpret the tests) differ by region.

Treatment

Syphilis is curable with antibiotics, especially when caught early:

• For early / infectious syphilis: usually one injection of benzathine penicillin G.
  
• For late latent or tertiary syphilis: multiple doses over weeks.
  
• Neurosyphilis requires IV treatment and specialist care.
  

After treatment, avoid sexual activity until your provider says it’s safe. Tell recent partners so they can get tested and treated too.

Protecting yourself

• Use condoms or barriers for vaginal, anal, oral sex.
  
• Avoid sex with someone who has a sore or rash until they have been tested and treated.
  
• Get regular STI screening if you have new or multiple partners.
  
• Talk openly with partners about STI status, history, and testing.
  

The Role of DoxyPEP in Preventing Syphilis

A newer tool being explored is DoxyPEP (doxycycline post-exposure prophylaxis). This means taking doxycycline after possible exposure to reduce the chances of getting syphilis.

• DoxyPEP has been shown to work in populations of gay, bisexual, and other men who have sex with men (gbMSM) and trans women who have had a recent bacterial STI.
  
• It’s taken 200 mg of doxycycline within 72 hours after condomless sex (one dose) and should not exceed 200 mg per day.
  
• DoxyPEP is not recommended in pregnancy because doxycycline can harm a developing fetus.
  
• There is concern about antibiotic resistance (i.e. bacteria becoming harder to treat). That risk is not fully known yet.
  
• Evidence for its effectiveness among people with vaginas (who are not pregnant) is limited, so its use is not yet broadly recommended in that group.
  
• Because syphilis rates are going up fast in Canada, some experts are calling for the rollout of doxyPEP in high-risk groups, with careful monitoring.
  

So DoxyPEP is a promising addition to prevention tools—but it’s not a replacement for condoms, testing, or treatment. It’s one option for people who are at higher risk and willing to weigh benefits and risks with a provider.

Dealing with Stigma

Talking about STIs can carry shame or fear. But here are some reminders:

• Having an STI does not define your worth.
  
• You can choose when, how, and with whom to share your status.
  
• Some settings (e.g. hookup apps, parties, darkrooms) make disclosure harder—plan ahead how and when you might talk about it.
  
• A sex-positive approach says: your health, pleasure, and safety all matter. Managing infections is part of caring for yourself and your partners.
  

Syphilis has been surging for a while in Canada, often hiding without symptoms. Because early signs are subtle or invisible, regular testing, lesion swabs, and follow-up care are essential.

DoxyPEP is a new tool with evidence in some groups (gbMSM, trans women) showing promise in preventing syphilis when used correctly—but it comes with cautions about pregnancy, antibiotic resistance, and limited data in other populations.

Together, using condoms, testing, treatment, honest conversations, and exploring new tools like DoxyPEP give you more control over your sexual health.
For more information, check out our Factsheet on Syphilis and the CATIE statement on DoxyPEP and Syphilis.