Epidemiology and Pathogenesis of Chlamydia trachomatis
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p515
2025-09-11
348
C. trachomatis causes significant infection and disease worldwide. In the United States, C. trachomatis is the most common sexually transmitted bacterial pathogen and a major cause of pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. An estimated 3 million cases of C. trachomatis infection occur annually in the United States. In 2010, more than 1.3 million cases of C. trachomatis infection were reported to the Centers for Disease Control and Prevention (CDC), corresponding to a rate of infection of 426 per 100,000 population and a 5.1% increase over the cases reported in 2009. In fact, of all the organ isms causing sexually transmitted disease reported to the CDC, only C. trachomatis cases have increased every year. Genital tract infections caused by C. trachomatis were identified most frequently in women between the ages of 15 and 24 years. It is important to note, however, that data reported to the CDC, especially with regards to Chlamydia, come as a result of screening programs that primarily target women between the ages of 15 and 24 years.
Ocular trachoma, on the other hand, is a much more prevalent disease, affecting 84 million individuals worldwide, with 7 to 9 million infections resulting in blindness. Remote rural areas of Africa, Asia, Central and South America, Australia, and the Middle East are hyperendemic for trachoma, where the prevalence rate of C. trachomatis is 60% to 90% in preschool children. Trachoma is the cause for 3% of the cases of blindness in individuals around the world, with adult women more likely to be affected as a result of their exposure to children who serve as the major reservoir of the organism.
C. trachomatis infections are primarily transmitted from human to human by direct contact with infected secretions. Some infections, such as neonatal pneumonia or inclusion conjunctivitis, are transmitted from mother to infant during birth. The various routes of transmission for C. trachomatis infection are summarized in Table1.
Table1. Primary Syndromes Caused by C. trachomatis
The natural habitat of C. trachomatis is humans. The mechanisms by which C. trachomatis cause inflammation and tissue destruction are not completely understood. The chlamydiae can infect a variety of different cells, including epithelial cells of the mucosa as well as blood vessels, smooth muscle cells, and monocytes. The chlamydial EB is phagocytosed into a host cell and resides in a vacuole that fails to fuse with a lysosome, leading to the intracellular persistence of the organism and escape from the host immune response. Chlamydiae are able to either turn on or turn off apoptosis (programmed cell death pathways) in infected host cells. By inducing host cell death, the organism facilitates its transmission to neighboring host cells and down-regulating inflammation in the acute disease process, whereas, by inhibiting apoptosis, the organism keeps the host cell alive, allowing for sustained survival in chronic infections.
The host’s immune response accounts for the majority of the tissue destruction following infection with C. trachomatis. Infected epithelial cells secrete pro-inflammatory cytokines including Interleukin-1α (IL-1α), tumor necro sis factor (TNF) and IL-6. Quickly upon infection, neutrophils and monocytes migrate to the mucosa and eliminate exposed EB. Later CD4 T helper cells migrate to the site of infection. Responding neutrophils and T helper cells release cytokines, resulting in the influx of additional immune cells. The importance of multiple, recurrent infection with C. trachomatis is associated with the development of ocular trachoma. Immunity provides little protection from reinfection and appears to be short lived following infection with C. trachomatis.
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