Treponema pallidum is a species of spirochaete bacterium with subspecies that cause treponemal diseases such as syphilis, bejel, pinta and yaws. It is not seen on a Gram stained smear because the organism is too thin.
There are at least four known subspecies:
- Treponema pallidum pallidum, which causes syphilis
- T. pallidum endemicum, which causes bejel
- T. pallidum carateum, which causes pinta
- T. pallidum pertenue, which causes yaws
There is some variation as to which are considered subspecies, and which are species. The cause of pinta is sometimes described as "Treponema carateum", rather than a subspecies of Treponema pallidum, even when the subspecies convention is used for the other agents.
This bacterium can be detected with special stains, such as the Dieterle stain.
Treponema pallidum is also detected by serology, including nontreponemal (VDRL, Rapid plasma reagin (RPR)) and treponemal antibody tests (FTA-ABS, Treponema pallidum immobilization reaction (TPI) and Syphilis TPHA test).
T. pallidum pallidum is a motile spirochaete that is generally acquired by close sexual contact, entering the host via breaches in squamous or columnar epithelium. The organism can also be transmitted to a fetus by transplacental passage during the later stages of pregnancy, giving rise to congenital syphilis. The helical structure of T. pallidum pallidum allows it to move in a corkscrew motion through a viscous medium such as mucus. It gains access to host's blood and lymph systems through tissue and mucous membranes.
The subspecies causing yaws, pinta, and bejel are morphologically and serologically indistinguishable from T. pallidum pallidum (syphilis); however, their transmission is not venereal in nature and the course of each disease is significantly different.
Full article ▸