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Treponema
ORGANISM:
- Genus: Treponema
- Species: pallidum, pertenue, carateum
GENERAL CONCEPTS:
- Three "treponematoses" are discussed: syphilis, yaws and pinta.
- Each of these diseases is characterized by distinct clinical stages. These stages are known as primary, secondary and tertiary.
- The primary stage involves multiplication of the bacteria at the site of entry to produce a localized infection.
- The secondary stage occurs following an asymptomatic period and involves dissemination of the bacteria to other tissues.
- The tertiary stage may occur after 20-30 years.
- The Treponema are highly invasive organisms; T. pallidum is the most invasive of the species, T. carateum the least invasive.
DISTINCTIVE PROPERTIES:
- The Treponema are motile, helically coiled organisms having a corkscrew-like shape. They stain very poorly because their thickness approaches the resolution of the light microscope.
- Treponema are delicate organisms requiring pH in the range 7.2 to 7.4, temperatures in the range 30°C to 37°C and a microaerophilic environment.
- The structure of these organisms is somewhat different: the cells have a coating of glycosamino-glycans, which may be host-derived, and the outer membrane covers the three flagella that provide motility.
- In addition, the cells have a high lipid content (cardiolipin, cholesterol), which is unusual for most bacteria. Cardiolipin elicits "Wassermann" antibodies that are diagnostic for syphilis.
- Treponema possess a complex antigenic makeup that is difficult to determine because the organisms cannot be grown in vitro.
PATHOGENESIS:
- Treponema pallidum is capable of infecting all body tissues.
- The disease caused by T. pallidum is syphilis. This is a relatively painless, slowly evolving disease. The host-parasite relationship leads to short symptomatic periods when the organism multiplies, followed by prolonged asymptomatic periods when host responses produce healing.
- Syphilis is strictly a person-person disease.
- An incubation period of from 10 to 90 days precedes the clinical presentation, despite the fact that the organisms disseminate immediately. The prominent feature of the disease is vascular involvement, particularly arterioles and capillaries.
- Treponemal antigen-host antibody complexes may cause some immunosuppression of the host and production of the distinct clinical stages:
- The primary stage occurs weeks to months following infection. The principal sign of infection is the hard chancre, generally found on the genitals. This lesion is essentially painless but filled with treponemes and is, therefore, highly contagious.
- The secondary stage occurs following an asymptomatic period of 2-24 weeks. In the secondary stage, a skin rash spreads from the palms and soles towards the trunk. This rash may last 2-6 weeks and is followed by recovery. On average, about 25% of patients experience relapses of the secondary stage.
- Following the secondary stage is a period of latency which may last many years and during which there are essentially no clinical symptoms.
- The tertiary stage may erupt following the period of latency and can affect all areas of the body and be fatal. Cardiovascular and neurological involvement are the most frequent causes of death. Typically, however, the appearance of lesions called "gummas" mark the tertiary stage. These lesions are, in fact, large granulomas resulting from hypersensitivity reactions and they can be extremely disfiguring.
- Syphilis that occurs in utero is termed congenital syphilis. About 50% of such fetuses abort or are stillborn. Of those surviving birth, two scenarios are observed: the "early" form shows symptoms that are apparent at birth; in the "late" form, infants appear normal until they are about 2 years old and only then display the traits known as "Hutchinson's triad", which include interstitial keratitis, notched incisors and eighth nerve deafness.
- Other treponematoses include:
- Yaws: Caused by T. pertenue, this disease occurs in tropical Africa, S. America, India, Indonesia and the Pacific Isles (equitorial regions). Symptoms involve the occurrence of a painless papule called the "Mother yaw" as the primary stage. Following healing and complete dissemination of the organisms, many papules return after 1-12 months and occur on the face and moist body areas.
- Pinta: Caused by T. carateum, this disease occurs only in tropical Central and South America. It is characterized by a painless papule (primary) followed 2-18 months later by secondary papules on the hands, feet and scalp. These lesions heal slowly after treatment (unlike syphilis, yaws).
HOST DEFENSES:
- It is the intricate interplay between the organism and the host immune system that defines the treponematoses.
- Immunity results in untreated persons but it is slow to evolve.
- Immunity is probably a combination of both humoral and cell-mediated defenses.
EPIDEMIOLOGY:
- Syphilis is found worldwide and is transmitted via sexual contact (ages 20-24 are most affected).
- Because the route of transmission is the same, 10% of gonorrhea patients also have syphilis.
- Yaws and pinta are not sexually transmitted and generally affect children or adolescents. These diseases are often geographically diagnosed.
DIAGNOSIS:
- Clinical: The clinical manifestations of the treponematoses are generally characteristic and readily identified.
- Laboratory: Darkfield examination of material from a chancre can show the presence of spirochetes. Immunological techniques including fluorescent treponemal antibody (FTA) or T. pallidum immobilization (TPI) can be of great assistance in observing the organisms. The Wassermann test looks for the presence of antibody against cardiolipin. Many other tests are also available.
CONTROL:
- Sanitary: As with other sexually transmitted diseases (STDs), use of a condom helps prevent infection.
- Immunological: None are available.
- Chemotherapeutic: Benzathine penicillin (long acting) or penicillin G are the drugs of choice. One must be aware of a possible Jarisch-Herxheimer reaction following treatment of secondary or tertiary syphilis, however. The rapid release of treponemal antigens after lysis by penicillin can cause hypersensitivity reactions in some persons.
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