The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and tertiary). Syphilis ( / ˈ s ɪ f ə l ɪ s/) is a sexually transmitted infection caused by the bacterium Treponema pallidum subspecies pallidum. Treponema pallidum usually spread by sex īlood tests, dark field microscopy of infected fluid Ĭondoms, Long-term monogamous relationships Electron micrograph of Treponema pallidum