Chlamydia is a genus of gram-negative bacteria which live as parasites within the cells of humans and other animals, causing a wide variety of diseases.
Some strains of chlamydia cause spontaneous abortions in flocks of sheep and goats; a vaccine is used to prevent the illness. Another vaccine-preventable strain causes eye infections in domestic cats.
Chlamydia psittaci causes psittacosis infections in birds such as pet parrots. Infected birds may become very ill and die; others are symptomless carriers. The disease may be transmitted to humans; it usually causes mild flu-like symptoms, but occasionally it turns into life-threatening pneumonia. The disease is easily treatable in both birds and humans with tetracycline.
In humans, the species Chlamydia trachomatis causes inclusion conjunctivitis and the venereal (sexually-transmitted) disease by the same name. Venereal chlamydial infections can be transmitted via vaginal, oral, or anal sex. Wearing a condom (male or female) can help prevent transmission.
In 1996, the World Health Organization estimated that 89 million people were infected with chlamydia worldwide. It is the most common treatable STD in the United Kingdom. The CDC estimates that 4 million people in the U.S. are infected every year, though only about half a million will seek treatment or be properly diagnosed. The low rate of diagnosis is due to symptomless infections and a lack of regular screening for the disease. The CDC estimates that 10% of teenage girls are infected. The economic cost of the disease in the U.S. is about $2 billion per year.
This STD causes symptoms such as abnormal genital discharge and pelvic pain (in women); infections from non-vaginal sex may cause rectal pain and sore throats. However, it often produces no symptoms at all. About 75% of infected women and 50% of infected men may have no overt signs of illness.
If left untreated, it can cause pelvic inflammatory disease in about 40% of infected women (which can lead to sterility and other problems due to damage to the fallopian tubes and uterus) and, if transmitted during birth, can cause severe eye infections and pneumonia in newborns. 18% of women with the disease will suffer from severe chronic pelvic pain, and 9% will have an ectopic pregnancy.
This infection is the single most common cause of infertility and sterility in women. Additionally, women with chlamydia have a 300-500% increased risk for contracting HIV, the virus that causes AIDS.
Men who are infected typically suffer from urethritis and swollen testicles. It is the most common cause of epididymitis in men under the age of 35. Some men also develop joint problems as a result of their infection. Some men also experience infertility and sperm damage.
Severe chlamydial infections are often mistaken for gonorrhea because the symptoms can be so similar.
Chlamydia is diagnosed by taking swabs of pus from the genitals to check for the presence of the bacteria directly, or by administering a urine test that checks for bacterial DNA. The urine test is newer and less invasive than the swab test, but it's also about twice as expensive.
It can be cured with antibiotics, typically azithromycin (a single dose) or doxycycline (a 7-day regimine.) Pregnant women might be given azithromycin, erythromycin, or occasionally amoxicillin. Penicillin has no effect on chlamydia infections.