Treponema pallidum

Treponema pallidum is the causative agent of syphilis, a sexually transmitted disease (STD). Other bacteria in the same genus cause the diseases yaws and bejel, which are transmitted through direct skin-to-skin contact or sharing of drinking vessels. T. pallidum has a characteristic helical shape, and is a member of the Spirochete family of bacteria. However, not all helical bacteria are Spirochetes:

• Spirilla, the majority of which are saprophytes
• Spiroplasma, including mycoplasmas
• Vibrio, Campylobacter and Helicobacter
• Spirochetes, a group of five genera, very widespread in nature and found in the fresh waters, of which only the first three are pathogenic for humans:
• Treponema
• Borrelia
• Leptospira
• Spirocheta
• Cristispira

This video shows a clinical specimen of syphilitic liver showning T. palludum (purple helices). The helical bacterial cells in this fixed specimen (~0.5 µm diameter, 10-25µm long) are no longer motile:

Spirochetes are simple bacteria, with less than 1000 genes.  Each type has a characteristic helical shape.  Some are tightly coiled like a telephone cord, while others are more open.  Very tight coils are seen in Leptospira, medium coils in Treponema and open coils are seen in Borrelia.  Spirochetes are Gram-negative and with a flagellar bundle running through their periplasmic space.  The spirochete flagella run in the perplasmic space, causing the cells to move in a corkscrew fashion. 

Syphilis is spread by mostly by sexual contact, except for congenital syphilis, which is spread from mother to fetus. Transmission by sexual contact requires exposure to moist lesions of skin or mucous membranes. As with many STDs, sexual promiscuity has resulted in an increase in syphilis during the last few decades. The symptoms of syphilis occur in three stages called primary, secondary and late:

• The first sign of syphilis is a lesion known as a "chancre" (a clean, painless, indurated ulcer) which forms at the site of entry where the organism enters the body through the mucous membranes or breaks in the epithelium. Multiple chancres occur if more than one organism enters. The chancre lesions contain an initially local infection by the Treponeme. Common sites for the lesions include genitalia, rectum, urethra and mouth. The chancre, which may be accompanied by swollen glands, may last from one to five weeks, and may disappear by itself even if no treatment is received.
• Approximately six weeks after the sore first appears, the second stage of the disease begins. The most common symptom during this stage is a rash, which may appear on any part of the body. Other symptoms may occur such as tiredness, fever, sore throat, headaches, hoarseness, loss of appetite, hair loss and swollen glands. These signs and symptoms will last two to six weeks and generally disappear in the absence of adequate treatment.
• The third stage, called late syphilis (syphilis of over four years' duration), may involve illness in the skin, bones, central nervous system and heart. Untreated, syphilis can lead to destruction of soft tissue and bone, heart failure, blindness and a variety of other conditions which may be mild to incapacitating. Women with untreated syphilis may transmit the disease to unborn children, which can result in death or deformity of the child.

Syphilis remains infectious for a period of up to two years, possibly longer. Transmission of infection depends on the existence of infectious lesions (sores), which may or may not be visible. No natural immunity to syphilis develops and past infection offers no protection to future exposure. Syphilis is relatively easily treated with antibiotics such as penicillin, usually given as consecutive daily intramuscular injections. Patients who are allergic to penicillin may be treated with tetracycline. Fortunately, unlike other STDs such as gonorrhea, there is little evidence of antibiotic resistance developing in syphilis.

Colour Atlas and Synopsis of Sexually Transmitted Diseases
by H. Hunter Handsfield
Full color views of common and uncommon sexually transmitted diseases. An invaluable tool for differential diagnosis of STDs, the atlas features one to two color photograph for each disorder and accompanies those with the salient points of epidemiology, clinical signs, physical exam, diagnosis and management. Therapy is expanded in this edition and new photographs are provided for the HIV, AIDS, opportunistic infections and much more.
(Amazon.co.UK)

Pox: Genius, Madness, and the Mysteries of Syphilis
Deborah Hayden
This brilliant book reveals the hidden impact of syphilis on many of history's famous figures - from Wilde to Hitler to Abraham Lincoln - and its influence on the culture they created. Was Beethoven experiencing syphilitic euphoria when he composed "Ode to Joy"? Did van Gogh paint "Crows Over the Wheatfield" in a fit of diseased madness right before he shot himself? Was syphilis a stowaway on Columbus's return voyage to Europe? Writing with remarkable insight and narrative flair, Hayden argues that biographers and historians have vastly underestimated the influence of what Thomas Mann called "this exhilarating yet wasting disease." Shrouded in secrecy, syphilis was accompanied by wild euphoria and suicidal depression, megalomania and paranoia, profoundly affecting sufferers' worldview, their sexual behavior and personality, and, of course, their art.
(Amazon.co.UK)