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Chlamydia is a common term for infection with any bacterium belonging to the phylum Chlamydiae. This term derives from the name of the bacterial genus Chlamydia in the family Chlamydiaceae, order Chlamydiales, class and phylum Chlamydiae, ultimately from Greek χλαμύδος "cloak". There are two genera in Chlamydiaceae: Chlamydia and Chlamydophila. The genus Chlamydia includes three species: C. trachomatis, C. muridarum, and C. suis. C. trachomatis infection is described below. Chlamydia trachomatis is a major infectious cause of human eye and genital disease. C. trachomatis is naturally found living only inside human cells and is one of the most common sexually transmitted infections in people worldwide — about four million cases of chlamydia infection occur in the United States each year. Not all infected people exhibit symptoms of infection. About half of all men and three-quarters of all women who have chlamydia have no symptoms and do not know that they are infected. It can be serious but is easily cured with antibiotics if detected in time. Equally important, chlamydia infection of the eye is the most common cause of preventable blindness in the world. Blindness occurs as a complication of trachoma (chlamydia conjunctivitis).[1]
SymptomsImage:SOA-Chlamydia-trachomatis-female.jpg Vaginal discharge due to chlamydia. Almost half of all women who get chlamydia and are not treated by a doctor will get pelvic inflammatory disease (PID), a generic term for infection of the uterus, fallopian tubes, and/or ovaries. PID can cause scarring inside the reproductive organs, which can later cause serious complications, including chronic pelvic pain, difficulty becoming pregnant, ectopic (tubal) pregnancy, and other dangerous complications of pregnancy. Chlamydia causes 250,000 to 500,000 cases of PID every year in the U.S. [1] Women infected with chlamydia are up to five times more likely to become infected with HIV, if exposed. [2] Chlamydia is known as the "Silent Epidemic" because in women, it may not cause any symptom and will linger for months or years before being discovered. Symptoms that may occur include: unusual vaginal bleeding or discharge, pain in the abdomen, painful sexual intercourse, fever, painful urination or the urge to urinate more frequently than usual. In men, chlamydia may not cause any symptoms, but symptoms that may occur include: a painful or burning sensation when urinating, an unusual discharge from the penis, swollen or tender testicles, or fever. Image:SOA-Chlamydia-trachomatis-male.jpg Unusual discharge from the penis.
Chlamydia may also cause reactive arthritis, especially in young men. (Some forms of reactive arthritis formerly were known as Reiter's syndrome. The latter term has fallen out of favor owing to revelations about Hans Reiter's Nazi past and in particular his active participation in horrific human experiments in concentration camps.) About 15,000 men develop reactive arthritis due to chlamydia infection each year in the USA, and about 5,000 are permanently affected by it. As many as half of all infants born to mothers with chlamydia will be born with the disease. Chlamydia can affect infants by causing spontaneous abortion; premature birth; conjunctivitis, which may lead to blindness; and pneumonia. DetectionDiagnostic testsThe diagnosis of genital chlamydial infections evolved rapidly from the 1990s through 2006. Nucleic acid amplification tests (NAAT), such as polymerase chain reaction (PCR), transcription mediated amplification (TMA), and the DNA strand displacement assay (SDA) now are the mainstays. As of January 2007, the most commonly used and widely studied chlamydia NAATs in the US and many other industrialized countries are Aptima (Gen-Probe), Probe-Tec (Becton-Dickinson), and Amplicor (Roche).Image:ChlamydiaTrachomatisEinschlusskörperchen.jpg Chlamydia trachomatis inclusion bodies (brown) in a McCoy cell culture. Because of improved test accuracy, ease of specimen management, convenience in specimen management, and ease of screening sexually active men and women, the NAATs have largely replaced culture, the historic gold standard for chlamydia diagnosis, and the non-amplified probe tests, such as Pace II (Gen-Probe). The latter test is relatively insensitive, successfully detecting only 60-80% of infections in asymptomatic women, and occasionally giving falsely positive results. Culture remains useful in selected circumstances and is currently the only assay approved for testing non-genital specimens. TreatmentC. trachomatis infection can be effectively cured with antibiotics once it is detected. Current Centers for Disease Control guidelines provide for the following treatments:
PathophysiologyChlamydiae replicate intracellularly, within a membrane-bound structure termed an inclusion. It is inside this inclusion, which somehow avoids lysosomal fusion and subsequent degradation, that the metabolically inactive "elementary body" (EB) form of chlamydia becomes the replicative "reticulate body" (RB). The multiplying RBs then become EBs again and burst out of the host cell to continue the infection cycle. Since Chlamydiae are obligate intracellular parasites, they cannot be cultured outside of host cells, leading to many difficulties in research. Diseases caused by Chlamydia trachomatisImage:SOA-conjunctivitis.jpg Conjunctivitis due to chlamydia. Chlamydia trachomatis can cause the following conditions:
Recent genetic discoveriesRecent phylogenetic studies have revealed that chlamydia shares a common ancestor with modern plants, and retains unusual plant-like traits (both genetically and physiologically). In particular, the enzyme L,L-diaminopimelate aminotransferase, which is related to lysine production in plants, is also linked with the construction of chlamydia's cell wall. The genetic encoding for the enzymes is remarkably similar in plants and chlamydia, demonstrating a close common ancestry. This unexpected discovery may help scientists develop new treatment avenues: if scientists could find a safe and effective inhibitor of L,L-diaminopimelate aminotransferase, they might have a highly effective and extremely specific new antibiotic against chlamydia. References
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