|Chlamydia trachomatis in brown|
(Busacca 1935) Rake 1957 emend. Everett et al. 1999
Chlamydia trachomatis (// //), an organism responsible for the most prevalent STD in the United States, is one of four bacterial species in the genus Chlamydia. C. trachomatis is a gram-negative bacterium. It is ovoid in shape and non-motile. The bacteria are non-spore-forming, but the elementary bodies act like spores when released into the host. The inclusion bodies of Chlamydia trachomatis were first described in 1942; the Chlamydia trachomatis agent was first cultured in the yolk sacs of eggs by Professor Tang Fei-fan et al in 1957.
C. trachomatis includes three human biovars:
- Serovars Ab, B, Ba, or C — cause trachoma: infection of the eyes, which can lead to blindness
- Serovars D-K — cause urethritis, pelvic inflammatory disease, ectopic pregnancy, neonatal pneumonia, and neonatal conjunctivitis
- Serovars L1, L2 and L3 — lymphogranuloma venereum (LGV).
Chlamydia can exchange DNA between its different strains, thus the evolution of new strains is common.
Chlamydia species are readily identified and distinguished from other Chlamydia species using DNA-based tests.
Most strains of C. trachomatis are recognized by monoclonal antibodies (mAbs) to epitopes in the VS4 region of MOMP. However, these mAbs may also cross-react with two other Chlamydia species, C. suis and C. muridarum.
Clinical signs and symptoms of C. trachomatis infection and Gonorrhea infection are indistinguishable. C. trachomatis is the single most important infectious agent associated with blindness (trachoma); approximately 84 million worldwide suffer C. trachomatis eye infections and 8 million are blinded as a result of the infection. Trachoma is a neglected tropical disease that has been targeted by the World Health Organization for elimination by 2020.
Treatment depends on the infection site, age of the patient, and whether another infection is present. It is possible to have a C. trachomatis and one or more other sexually transmitted infections at the same time. Treatment is often done with both partners simultaneously to prevent reinfection. C. trachomatis may be treated with several antibiotic medications. These include: azithromycin, erythromycin or ofloxacin.
If treatment is necessary during pregnancy levofloxacin, ofloxacin and doxycycline are not prescribed. In the case of a patient that is pregnant the medications typically prescribed are azithromycin, amoxycillin and erythromycin. Amoxycillin has fewer side effects than the other medications for treating antenatal C. trachomatis infection. Retesting during pregnancy can be performed three weeks after treatment. If the risk of re-infection is high, screening can be repeated throughout pregnancy.
If the infection has progressed, ascending the reproductive tract and pelvic inflammatory disease develops, damage to the fallopian tubes may have already occurred. In most cases the C. trachomatis infection is then treated on an outpatient basis with ofloxacin, levofloxacin, metronidazole, ceftriaxone, probenicid, and/or doxycycline. Don't forget to treat the mother of an infant with C. trachomatis of the eye, which can evolve into a pneumonia 
- Nucleic acid amplification tests (NAAT). These tests find the genetic material (DNA) of Chlamydia bacteria. These tests are the most sensitive tests available, meaning that they are very accurate and that they are very unlikely to have false-negative test results. A polymerase chain reaction (PCR) test is an example of a nucleic acid amplification test. This test can also be done on a urine sample.
- Nucleic acid hybridization tests (DNA probe test). A probe test also finds Chlamydia DNA. A probe test is very accurate but is not as sensitive as nucleic acid amplification tests.
- Enzyme-linked immunosorbent assay (ELISA, EIA). This quick test finds substances (Chlamydia antigens) that trigger the immune system to fight Chlamydia infection.
- Direct fluorescent antibody test (DFA). This quick test also finds Chlamydia antigens.
- Chlamydia cell culture. A test in which the suspected chlamydia sample is grown in a vial of cells. The pathogen infects the cells and after a set incubation time (48 hours) the vials are stained and viewed on a fluorescent light microscope. Cell culture is more expensive and takes longer (two days) than the other tests. The culture must be grown in a laboratory.
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