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Chapter 33 : Chlamydiae
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Chlamydiae are obligate intracellular bacteria which cause many diseases in animals and humans. Originally they were classified as Chlamydia trachomatis, C. pneumoniae, C. psittaci, and C. pecorum. During their growth, chlamydiae produce characteristic intracytoplasmic inclusions that can be visualized by Giemsa stains or direct fluorescent antibody (DFA) stains of infected patient material, such as conjunctival scrapings, as well as cervical or urethral epithelial cells. Chlamydiae are phagocytized by susceptible host cells. The chlamydiae possess group (genus)-specific, species-specific, and type-specific antigens. The major outer membrane protein contains species-, subspecies-, and serovar-specific antigens. Chlamydiae cause the recruitment of lymphocytes to the site of infection by inducing the release of local host factors, which influence the adhesion cascade of cytokines and adhesion molecules. By adult life, active infection is infrequent, but the sequelae of the disease result in blindness. Worldwide, trachoma is considered the most common cause of preventable blindness. C. trachomatis is the most common sexually transmitted bacterial pathogen. Sensitivity and specificity of diagnostic tests for the detection of C. trachomatis have been provided in this chapter. The most widely used serological test for diagnosing chlamydial infections is the genus-specific complement fixation (CF) test. It is useful in diagnosing psittacosis, in which paired sera often show fourfold or greater increases in titer. There are some commercially available serologic tests based on measurement of antibodies reactant to chlamydial inclusions in cell culture or enzyme immunoassay (EIA) using chlamydial antigens.
Sensitivity and specificity of diagnostic tests for the detection of C. trachomatis