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Chlamydia
ORGANISM:
- Genus: Chlamydia
- Species: trachomatis, psittaci
GENERAL CONCEPTS:
- The Chlamydia are obligate intracellular parasites.
- C. trachomatis is responsible for the diseases trachoma, inclusion conjunctivitis, lymphogranuloma venereum (LGV) and nongonococcal urethritis (NGU). In other words, oculourogenital infections.
- C. psittaci produces systemic diseases including psittacosis, ornithosis and pneumonitis.
DISTINCTIVE PROPERTIES:
- The Chlamydia have an unusual developmental cycle that involves two distinct forms: infectious elementary bodies and intracellular reticulate bodies. Elementary bodies attach and are internalized by susceptible host cells. Once inside, they reorganize into a replicative form (the reticulate body). Over a 24 hour period, these reticulate bodies divide and begin to reorganize back into elementary bodies. About 48-72 hours after infection, the cell is lysed and numerous infectious elementary bodies are released.
- The genome of Chlamydia is only 25% the size of E. coli, making it one of the smallest prokaryotes.
- The pathogenic mechanisms employed by Chlamydia are not well understood.
PATHOGENESIS:
- C. trachomatis is spread via the fingers to the urogenital area and vis versa. In contrast, C. psittaci is acquired from infected birds, usually via the respiratory route.
- Trachoma is an infection of the epithelial cells of the conjunctiva, producing inclusion bodies. Vascularization and clouding of cornea along with trichiasis (inward growth of eyelashes) can produce scarring that may lead to blindness.
- Inclusion conjunctivitis is a milder form that occurs in both children and adults. This form generally heals without scarring or blindness.
- Sexually transmitted nongonococcal urethritis (NGU) is similar to gonorrhea and occurs with greater frequency. In 1997, approximately 320,000 cases were reported to the Centers for Disease Control.
- In men, a condition termed lymphogranuloma venereum (LGV) involving inguinal lymphadenopathy ("buboes") can occur.
- Psittacosis is a respiratory disease ranging from influenza-like to pneumonia-like and is generally acquired from infected birds.
HOST DEFENSES:
- Chlamydia induce interferon and are sensitive to it.
- During infection, antibodies are synthesized but recovery is not generally protective.
EPIDEMIOLOGY:
- Trachoma is prevalent in Africa and Asia, generally in hot and dry areas.
- The organisms are very persistent. Their habitat is similar to that of Neisseria and Haemophilus.
- Infection can occur via swimming in unchlorinated pools, sharing towels or by passage through the birth canal.
DIAGNOSIS:
- Clinical: Diagnosis of trachoma is usually good. Likewise, the genital vesicles associated with LGV are characteristic. NGU can only be suspected in the absence of laboratory findings.
- Laboratory: Iodine stained specimens usually show inclusion bodies that represent the replicating bacteria. The Chlamydia can be cultured in tissue culture and appropriate serological tests performed.
CONTROL:
- Sanitary: Good hygiene, treatment of sexual partners and the quarantine of birds all reduce the incidence.
- Immunological: No vaccine is available or likely since specific antibodies fail to neutralize elementary bodies in vivo.
- Chemotherapeutic: Tetracycline or erythromycin are drugs of choice.
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