by Courtney Helman
Disease Name: Chlamydia
Means of Transmission: Direct contact through sex (vaginal, anal, oral) or during vaginal childbirth if the mother is infected (2)
Usual Reservoirs: Human
Etiologic Agent: Chlamydia trachomatis (6)
General Characteristics: Chlamydia trachomatis is an obligate intracellular, Gram-negative bacterium (4). It is a dimorphic bacterium with a two-phase life cycle. It exists as either an elementary body or a reticulate body. The dangerous communicable form is the smaller elementary body, and attaches and enters the host cell, while the reticulate body is the larger, intracellular form, which promotes metabolic activity and reproduction through binary fission (4). This bacterium is parasitic and heavily depends on the host in order to perform its metabolic as well as reproductive processes (1).
Key Tests for Identification: One of the best ways to identify this bacterium is isolating it is a culture. Antigen detection methods include enzyme immunoassays and direct fluorescence antibody assays. These tests are more cost and time efficient than cell culture isolation, and are more commonly used. Other tests include DNA hybridization probe tests, and “nucleic acid amplification tests based on polymerase chain reaction, ligase chain reaction, and transcription-mediated amplification technology (8).” Nucleic acid amplification techniques are now being used with urine specimens, which is much less invasive than obtaining a genital swab. Also, duplex tests are being administered to simultaneously detect Chlamydia and Gonorrhea (8).
Historical Information: Professor Tang Feifan isolated Chlamydia trachomatis in the yolk sac of a chicken embryo in 1957 in China (5). The genus corresponds to the phylum it belongs to, Phylum Chlamydiae. The bacterium was first associated with trachoma, an eye disease, explaining the species name (5).
Signs and Symptoms: Unfortunately in 80% of women and 50% of men, Chlamydia produces no signs or symptoms (7). However, symptoms associated with Chlamydia include abdominal and cervical pain, bleeding between menstrual cycles, abnormal vaginal or anal discharge, and fever in women. In men symptoms include unilateral abdominal pain, enlarged scrotum, abnormal anal or urethral discharge, and fever in males. In infants, conjunctivitis, eye secretions, and other ocular problems can indicate Chlamydia (7). Chlamydia can lead to more serious problems including PID (pelvic inflammatory disease), genital ulcers caused by lymphogranuloma venereum, increased rate of cervical cancer and Reiter syndrome, infertility, and chronic conjunctivitis and blindness in infants (7).
Virulence Mechanisms: Chlamydia trachomatis’ ability to grow and reproduce inside the host contributes to its virulence. It is unclear how the elementary bodies attach and penetrate the host cells for entry, however, once they gain entrance into the cell and are phagocytized they transform into reticulate bodies that live in a membrane bound vacuole. The vacuole prevents phagolysosome fusion, allowing the reticulate bodies to replicate and eventually transform back into the infectious elementary bodies in the phagosome. The elementary bodies are released by host cell lysis or through fusion of the vacuole’s plasma membrane with the host cell’s plasma membrane (5,8). This life cycle not only evades the host’s immune system, but also uses the host’s immune system to proliferate.
Control or Treatment: Antibiotics easily treat and cure Chlamydia. The two most common antibiotics used to treat Chlamydia are azithromycin and doxycycline. Azithromycin is only taken once, while doxycycline is taken for a week (2). Other means of control include informing previous and current sex partners of infected individuals. Also, abstaining from sex until treatment is completed or until the infected person tests negative can control re-infection (2).
Current Outbreaks: According to the Centers for Disease Control and Prevention (CDC), Chlamydia is one of the most common and prevalent STD’s in the United States. 976,445 Chlamydia infections were reported in the United States in 2005, indicating a rate of 332.5 cases per 100,000 people (3). Also, in the same year, the reported number of women infected by Chlamydia was more than three times higher than the reported number of men infected. Women between the ages of 15-19 and 20-24 comprised the highest percentage of women infected, with rates over 2,600 cases per 100,000 women (3). According to the World Health Organization, in 1999, there were an estimated 92 million new cases of Chlamydia in the world. Of the estimated 92 million cases, South and Southeast Asia comprised the most with 43 million cases, Sub-Saharan Africa followed with 16 million cases, Latin America and the Caribbean followed with 9.5 million cases, Eastern Europe and Central Asia had 6 million cases, East Asia and the Pacific had 5.3 million cases, Western Europe had 5 million cases, the United States had 4 million cases, North Africa and the Middle East had 3 million cases, and Australia and New Zealand had the least amount of new cases with only 340,000 cases (9).
Prevention: The best preventative mechanism is to abstain from sex. However, if one chooses to have sexual contact, ways to prevent Chlamydia infection include regular annual screening for Chlamydia, having sex with people who have been tested and are not infected, and consistent and proper use of a latex condom when having sex (2).
1. Becker, Yechiel. "Chlamydia." Medical Microbiology. 1996. The University of Texas Medical Branch of Galveston. 30 APR 2007 <http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.2157>.
2. "Chlamydia." CDC Fact Sheet APR 2006 30 APR 2007 <http://www.cdc.gov/std/chlamydia/STDFact-Chlamydia.htm>.
3. "Chlamydia." STD Surveillance 2005. 2005. Centers for Disease Control and Prevention. 3 May 2007 <http://www.cdc.gov/std/stats/chlamydia.htm>.
4. "Chlamydia trachomatis." BUGS Database. SEP 2000. 30 APR 2007 <http://medinfo.ufl.edu/year2/mmid/bms5300/bugs/chlamtra.html>.
5. Ward, Michael. "Chlamydiae." Chlamydiales and Chlamydia. NOV 2002. 30 APR 2007 <http://www.chlamydiae.com/docs/Chlamydiales/Chlamydialeshistory.asp>.
6. Robinson, Angela. "Chlamydia- the silent epidemic." NetDoctor 09 DEC 2005 30 APR 2007 <http://www.netdoctor.co.uk/womenshealth/facts/chlamydia.htm>.
7. Houry, Debra E. "Chlamydia." eMedicine 10 MAY 2006 03 MAY 2007 <http://www.emedicine.com/emerg/topic925.htm>.
8. Peeling, Rosanna W. and Robert C. Brunham. "Chlamydiae as Pathogens: New Species and New Issues." Emerging Infectious Diseases Volume 2 OCT 1996 [307- 319]. 02 MAY 2007 <http://www.cdc.gov/ncidod/EID/vol2no4/peeling.htm>.
9. "Estimated new cases of Chlamydial infections." Global Prevalence and Incidence of Selected Curable Sexually Transmitted Infections. 2001. World Health Organization. 3 May 2007 <http://www.who.int/docstore/hiv/GRSTI/pdf/figure04.pdf>.