All this talk of Lyme disease is getting me all excited about spirochetes. Borrelia burgdorferi, the bacterium that causes Lyme disease, is a spirochetal bacterium, and so is Treponema pallidum, the spirochete that causes syphilis. Now, if you're thinking syphilis is all about sores on the naughty bits, you're missing the best parts of the story. Syphilis is a rather serious and common disease, and can increase the transmission of other STD's such as HIV. If left untreated it can be disabling and deadly.
Treponema pallidum, the bacteria that causes syphilis. How cool is that? (courtesy the CDC)
T. pallidum cannot be cultured outside of the human body. That means unlike Strep, for instance, we can't just grow it in the lab and watch what it does. Much of our knowledge of the disease was acquired during the pre-antibiotic era and from the infamous Tuskegee Syphilis Study.
Anyway, the disease we call syphilis is divided into three stages, each of which is fascinating on its own. In contrast to, say, "chronic" Lyme disease, antibodies can be detected in the blood of people with this disease, and correlate with disease activity.
Syphilis is almost always sexually transmitted, and very effectively at that. It causes this lesion, called a "chancre", which despite it's horrid appearance is quite painless. These chancres can occur anywhere on the body, and being painless, can hide rather effectively (in the mouth, say). Left untreated, they'll clear up on their own. This is not a good thing. If penicillin is given at this stage, the infection can be cured. If you simply let your chancre disappear on its own, you're in a bit more trouble. While the lesion is healing, the spirochete is moving in and finding cozy spots throughout the body.
Weeks to months after the chancre goes away, a new rash may appear (this happens in about a quarter of patients). One of its common characteristics is its appearance on the palms and soles, which is less characteristic of most other rashes. Other symptoms may also appear, such as headache, swollen glands, and fever, but the rash and any other symptoms also disappear on their own. If you once again ignore the illness, you've just lost your second opportunity for a cure. At this point, the disease goes into the "latent" phase, and the real fun begins.
This is some really bad stuff. Tertiary, or "late latent" syphilis can cause an inflammation of the blood vessels leading to among other things deadly aortic valve disorders. More common these days is neurosyphilis, an infection of the central nervous system. This can lead to tabes dorsalis, a disorder of the spinal cord that can be painful and can lead to a severely impaired ability to walk. It also causes "generalized paresis of the insane". People with neurosyphilis often have a characteristic high-stepping gait, and may become quite demented. (They also have some classic eye findings, but that's more for pimping med students.) Unfortunately, treatment at this point often does little to reverse the disease, but can halt further progression.
Syphilis is a well-studied disease. There is no vaccine, but it is easily preventable (or would be if we weren't horny, irresponsible mammals). It's also easy to cure, if caught relatively early. If it's not caught early, the patient becomes very interesting, and no one wants to be an interesting patient.