Treponema pallidum is a bacterial species in the spirochete family. The bacterium is helically coiled and causes several infectious diseases.
What is Treponema pallidum?
Treponema pallidum represent a species of gram-negative, helical bacteria in the spirochete family. Spirochetes themselves are characterized by an unusually long (about 5 to 250 µm), thin (diameter about 0.1 to 0.6 µm), and spirally curved shape. The species Treponema pallidum can be further subdivided into several subspecies, each of which causes different infectious diseases. For humans, they are obligate pathogens. Thus, it also infects healthy and immunocompetent hosts and causes disease in them.
Occurrence, distribution, and characteristics
Treponema pallidum is a species of the spirochetes, which in turn are primarily found as free-living bacteria in soils, waters, as well as aquatic mud. Treponema pallidum does not survive long outside of humans, however, because it is sensitive to heat, drought, cold, and other environmental conditions. Treponema pallidum is found only in humans. Transmission of the bacterium is only possible through direct contact with the mucous membranes of an infected person. Infection usually occurs during sexual intercourse. Treponema pallidum penetrates the skin or mucous membrane through the smallest injuries, usually in the genital and anal areas. Rarely, infection can also occur through the oral cavity or infected objects. In addition, an infected mother can transmit Treponema pallidum to her unborn child beginning in the 4th month of pregnancy. Theoretically, transmission via blood transfusion is also possible, but practically excluded due to systematic controls in Germany. Treponema pallidum has a length of 5 to 15 µm and a width of about 0.2 µm. The bacterium has between 10 and 20 coils and moves by rotation around its longitudinal axis. Treponema pallidum has very fine structures, making it difficult to visualize even with staining under the microscope. However, live observations can be made with dark-field microscopy. The pathogens are detected by serological blood testing. Since Treponema pallidum is a pathogenic bacterium, it causes infectious diseases that require treatment. Cure of the respective disease is only possible by administration of antibiotics. In connection with transmission, it is important to note that condoms are effective in protecting against the sexually transmitted pathogen, but do not provide 100 percent protection against infection. To avoid infection, infected persons should therefore refrain from sexual intercourse. If Treponema pallidum is detected, the diagnosing laboratory must submit a non-name report to the RKI. If local spread occurs, the responsible health authority as well as physicians in the region must be informed in order to take preventive measures against further spread. This is especially the case with syphilis caused by Treponema pallidum pallidum.
Diseases and symptoms
Treponema pallidum causes different diseases depending on the subspecies. Syphilis is probably the best-known disease, triggered by Treponema pallidum pallidum. It is a sexually transmitted infectious disease, also known as syphilis, lues venerea or hard chancre. Syphilis is transmitted primarily during sexual acts through contact with mucous membranes. Infection is also possible during childbirth, when an infected mother transmits the pathogen to her child. In this case, it is called syphilis connata. Syphilis shows a very varied appearance. Characteristic are painless ulcers on mucous membranes and swelling of the lymph nodes at the beginning of the disease. A chronic course is also possible, which is characterized by multiple infestations of the skin and organs. In the final stage of syphilis, the disease causes destruction of the central nervous system. The first symptoms appear about three weeks after infection. Syphilis progresses in 4 stages. Primary syphilis results in the formation of a painless nodule at the site of infection, which is highly contagious. Swelling of the lymph nodes also occurs, but in some circumstances physical changes may not occur.This phase is followed by secondary syphilis, in which the pathogen spreads throughout the body via blood and lymphatic channels. It is characterized by changes in the skin and mucous membranes and the formation of scaly and/or purulent vesicles and is also highly contagious. After a silent and sometimes long-lasting phase, tertiary syphilis occurs, with the onset of symptoms such as nodules on the mucosa. These then break down into ulcers, and the destruction of muscles, skin and organs also progresses. At this stage of syphilis, mental and neurological deficits (e.g., dementia) may occur. The final stage is quaternary syphilis (neurosyphilis). It is often asymptomatic, but without treatment, tissue in the brain slowly perishes. If syphilis is congenital, children often have mental and/or physical disabilities and are born deficient or premature. If syphilis has been diagnosed, treatment is with antibiotics such as penicillin. This makes syphilis curable. Endemic syphilis (Bejel) is caused by the bacterium Treponema pallidum endemica. It is an infectious disease that is not sexually transmitted. Transmission occurs by smear infection in close social contact. Primarily, nonvenereal syphilis occurs in children between 4 and 10 years of age living in the arid areas of Africa, the Arabian Peninsula, and the Middle East. Treatment is with penicillin for a period of at least 2 weeks; severe cases require longer treatment. Pinta skin disease is caused by Treponema pallidum carateum and occurs mainly in Central and South America and Mexico. It is a so-called tropical treponematosis in which depigmented or hypopigmented skin areas occur in the course of the disease. These are called leukoderma. Transmission occurs through skin contact, and symptoms appear after about 1 to 3 weeks. In most cases, pinta is chronic and lasts for years; therapy is usually with benzylpenicillin. Treponema pallidum pertenue is the causative agent of the non-venereal infectious disease frambösie, which occurs primarily in tropical regions. The name is derived from the French word for raspberry (framboise). The name is also used to describe the typical changes in the skin. The chances of cure are good when treated with penicillin. The infectious diseases caused by the pathogens of the species Treponema pallidum cannot be prevented with a vaccine.