@Lube_Man we actually diagnose syphilis in five stages: Primary, Secondary, Early Latent, Late Latent & Tertiary. The different stages have to do with the kind of symptoms present, the infectiousness (whether you can pass it on to someone), and how long a person has had the infection. The staging will also determine how long antibiotics are needed.
You may be interested to know that Syphilis is only contagious in the first two years (primary & secondary stages) and tertiary syphilis is now very rare!