Syphilis can be acquired or congenital.
Acquired syphilis is via the time honoured manner
. The infection then goes through 3 phases, of which the second phase is the most infectious and the time when a sexual partner is most likely to catch it. A person may not even know that they have caught it initially as the first phase is characterised by a painless ulcer and that ulcer might be somewhere out of sight. The second phase can take usually 2- 10 months to appear. The third phase can take up to 20 years to become evident (though often would be quicker than that - but years, not months). During the third phase, the long term problems become evident. The commonest long term problems were neurological, including a type of dementia, or heart problems, but syphilis is “the great imitator” and can affect any part of the body. But the patient is no longer infectious at this point.
If a woman is suffering from early (1st or 2nd stage) syphilis whilst pregnant, the infection can be passed across the placenta to the baby - so the baby catches syphilis before birth, not during delivery. Affected babies are basically born with secondary syphilis. However, it’s not a given that the baby will be affected if the mum is infected, and I’ve seen evidence of the truth of this statement in real life.
Treatment nowadays is easy - just antibiotics - and pregnant women in the UK are routinely screened for syphilis with blood tests. Those blood tests will also occasionally pick up other non-syphilitic diseases, rare in the UK but common in some parts of the world (yaws and pinta).
DOI: i used to work in the field of sexual medicine.