Articles on Medical Diseases and Conditions

Tag: Spirochetal

  • Cardiolipin Tests

    The first practical serologic test for syphilis (STS) was the complement fixation (CF) technique invented by Wassermann. He used extract from a syphilitic liver as the antigen that demonstrated the presence of antitreponemal antibodies. Subsequently it was found that the main ingredient of the substance he used actually had nothing to do with syphilitic infection and was present in other tissues besides liver. It is a phospholipid that is now commercially prepared from beef heart and therefore called cardiolipin. The reagent used in current screening tests for syphilis (as a group, sometimes called STS) is a mixture of purified lipoproteins that includes cardiolipin, cholesterol, and lecithin. Apparently, an antibody called “reagin” is produced in syphilis that will react with this cardiolipin-lipoprotein complex. Why reagin is produced is not entirely understood; it is not a specific antibody to T. pallidum. There is a lipoidal substance in spirochetes, and it is possible that this substance is similar enough to the cardiolipin-lipoprotein complex that antibodies produced against spirochetal lipoidal antigen may also fortuitously react with cardiolipin.

    The original Wasserman CF test was replaced by a modification called the Kolmer test; but this in turn was replaced by the much faster, easier, and cheaper flocculation tests. In earlier versions of the flocculation reaction the patient’s serum was heated; for unknown reasons, heating seemed to enhance the reaction. Then a suspension of cardiolipin antigen particles is added to the serum and mixed. In a positive (reactive) test result, the reagin antibody in the patient serum will combine with the cardiolopin antigen particles, producing a microscopic clumping or flocculation of the antigen particles. The reaction is graded according to degree of clumping. The current standard procedure for this type of test is the Venereal Disease Research Laboratory (VDRL) test. It was found that the preliminary heating step could be eliminated if certain chemicals were added to the antigen; this modification is called the rapid plasma reagin (RPR) test and gives results very similar to those of the VDRL.

    Drawbacks of the cardiolipin serologic tests for syphilis

    Variation in test modifications. Not all sera from known syphilitics gave positive reactions in these tests. It was discovered that the number of positives could be increased by altering the ratio of antigen ingredients. However, usually when the percentage of positive results increases significantly, more false positives are reported. One report indicates that about 2% of VDRL or RPR tests in primary and secondary syphilis are falsely negative due to antigen excess (prozone phenomenon).

    Effect of antibiotic therapy. A peculiarity of the STS exists when antibiotic treatment is given. If the patient is treated early in the disease, the STS will revert to nonreactive state. In patients with primary syphilis, one study found that the VDRL or RPR returned to nonreactive state in 60% of patients by 4 months and 100% of patients by 12 months. In secondary syphilis, the VDRL became nonreactive in 12-24 months. Another study of patients with primary and secondary syphilis reported that successful treatment usually produced a fourfold decrease in VDRL titer by 3 months and an eightfold decrease by 6 months. The VDRL decline may be slower if the patient had other episodes of syphilis in the past. However, the longer the disease has been present before treatment, the longer the VDRL takes to become nonreactive. In many cases after the secondary stage it will never become nonreactive, even with adequate treatment (this is called “Wassermann fastness”).

    Spontaneous loss of test reactivity. In tertiary syphilis, there is a well-documented tendency for a previously reactive VDRL/RPR test result to revert spontaneously to nonreactive, even if the patient is untreated. This is reported to occur in about 20%-30% (literature range, 5%-45%) of patients.

    Biologic false positive reactions. Some patients have definitely positive results on RPR but just as definitely do not have syphilis or any exposure to it. These are called biologic false positive (BFP) reactions. The major known causes of BFP reactions can be classified under three headings:

    1. Acute BFP reactions, due to many viral or bacterial infections and to many febrile reactions such as hypersensitivity or vaccination. These usually give low-grade or moderate (1 to 2 +) STS reactions and return to normal within a few weeks.
    2. Chronic BFP reactions, due to chronic systemic illness such as antiphospholipid antibodies (Chapter 8), rheumatoid-collagen diseases, malaria, or chronic tuberculosis. There is also an increased incidence of BFP reactions in old age. Whereas there is less than 2% incidence of BFP reactions in men before the age of 60 years, some studies report an incidence as high as 9%-10% after age 70.
    3. Nonsyphilitic treponemal diseases such as yaws, pinta, Borrelia (Lyme disease), or relapsing fever.

    Summary. The cardiolipin STS is cheap, easy to do, and suitable for mass testing. Its sensitivity and specificity are adequate, and positivity develops reasonably early in the disease. Reagents are well standardized and reproducibility is good. Disadvantages are relatively poor sensitivity in primary syphilis, the tendency in late syphilis for spontaneous reversion of a reactive test result to a nonreactive result, and the problem of BPF reactions. To add further to the confusion, some patients with BFP reactions may have syphilis in addition to one of the diseases known to give BFP reactions. Because of this, everyone hoped for a way to use T. pallidum organisms themselves as antigen rather than depend on the nonspecific reagin system.

  • Immunologic Tests

    Immunologic tests for syphilis depend on the fact that the diseases caused by infectious organisms are characterized by development of antibodies toward that organism. These antibodies may be specific or nonspecific (Table 15-1). Nonspecific antibodies may be either of the cross-reacting type (sharing a common antigen with another organism) or of the fortuitous type (provoked by some nonspecific portion of the organism).

  • Dark-Field Examination

    Dark-field is a wet-preparation method for direct visualization of living T. pallidum spirochetes in material from syphilitic lesions. A microscope with a special dark-field condensor is required. This condensor prevents light from passing directly through the slide being viewed into the microscope viewing lenses but instead forces the light to pass to the periphery of the slide. Objects on the slide reflect some light up into the viewing lenses, so the objects appear white on a dark background. Dark-field was the only way to make the laboratory diagnosis of syphilis before serologic tests were available. The usual indications for this test are suspected primary stage syphilitic lesions and any suitable secondary stage lesion. Dark-field examination may be the only way to make a diagnosis early in the primary stage, since immunologic test antibodies often do not appear until late in the primary stage. Obtaining the specimen without contamination by blood or surface bacteria is very important. The lesion should be cleansed thoroughly with water or 0.85% saline and a sterile gauze pad. No soap or antiseptics should be used. Care must be taken not to produce bleeding, since red blood cells (RBCs) will obscure the organisms. After the lesion is blotted dry, a clear serous exudate should accumulate in a few minutes. If it does not, the lesion may be abraded gently with gauze, but not enough to cause bleeding. The serous fluid exudate is drawn off in a pipette or capillary tube for examination with a dark-field microscope. The causative organism, T. pallidum, has a characteristic morphology and motility on dark-field examination, but experience is necessary for interpretation, since nonpathogenic varieties of spirochetes may be found normally in the genital areas. Sensitivity with reasonable experience is reported to be about 75%. Dark-field examination by experienced personnel is no longer widely available in many areas because it is rarely ordered. If it is unavailable, a serologic test using the fluorescent treponemal antibody-absorbed (FTA-ABS) method could be substituted. However, the FTA-ABS test will miss 10%-20% of cases, with the possibility of error being greatest in the first week of the primary stage.

  • Syphilis

    Syphilis is caused by the spirochete Treponema pallidum. Clinical syphilis usually is subdivided into primary, secondary, latent, and tertiary (late) stages. The primary stage begins after an average incubation period of 3-6 weeks (range, 1.5-13 weeks) and is manifested by the development of a primary stage shallow ulcer, or chancre, near the site of infection. The time of appearance is variable, and the lesion often is inconspicuous and overlooked, especially in the female. The primary stage lasts about 4-6 weeks (range, 2-8 weeks) during which the chancre usually heals, followed by the secondary stage, which lasts about 4-12 weeks. About 80% of patients develop a rash, which in addition to other areas typically involves the palms and soles. Mucous membranes are involved in about 60% of cases. There is generalized lymphadenopathy in 75%. Asymptomatic central nervous system (CNS) involvement has been documented in up to 30% of patients. During the last part of the secondary stage the visible lesions disappear and the patient enters the latent stage. This lasts, on the average, 3-5 years. About 25% of patients relapse temporarily into active disease during the first 1-2 years. By the end of the latent period about one half of untreated patients apparently achieve spontaneous cure or at least do not develop further evidence of the infection. About 25% remain in a latent (“late latent”) status, and the remaining 25% develop tertiary stage sequelae such as neurologic, cardiovascular, or ocular syphilis.

    Diagnostic procedures in syphilis include dark-field examination, immunologic tests, and cerebrospinal fluid (CSF) examination, depending on the clinical situation.