Ah, sorry Amy - I didn't double-check first, but does make sense that syphilis is also an oral risk. And it is indeed a nasty bugger, as it's so easy to miss the primary symptom (chancre) and even the secondary ones (rash and joint pains etc.) so unless you're tested you can head into unpleasant tertiary symptoms easily, and it's very difficult to treat then.
Yikes:
The findings in this report suggest that during 2000-2002, 13.7% of syphilis cases in Chicago were attributed to oral sex, including 20.3% of cases among MSM. Other reports also have associated oral sex with transmission of syphilis; one third of MSM who were involved in syphilis outbreaks in Brighton and Manchester, United Kingdom, acquired syphilis through oral sex.