Chlamydia is the most sexually transmitted disease in the US, infecting almost five million people every year. It is three times more common than gonorrhea, six times more common than genital herpes, and thirty times more common than syphilis.
Chlamydiae is a class of Gram-negative bacteria once thought to be viruses because they are not able to reproduce without attaching to other cells. They do possess all the features needed for independence, except the ability to generate their own energy. Therefore, they are known as ‘energy parasites’ – or scientifically speaking “obligate intracellular parasites.” Either way, it means they steal from the host to fuel their own metabolism because they that lack the ability to grow outside of host cells. This class is similar to the Rickettsiae, but its diseases are less severe but far more common. Chlamydiae contains zoonotic species with animals, acting as both reservoirs and vectors.
Incubation is seven to fourteen days after exposure, and a person can be infectious for several years, if not treated. There is no immunity; therefore, a person can be reinfected. If left untreated, a woman will suffer the most since there are no symptoms. The bacteria can spread from the cervix to other parts of the reproductive system, causing infertility or tubal pregnancies. A fetus cannot contract it within the womb, but only as it passes through the birth canal. Babies born from infected mothers develop conjunctivitis before they are two weeks old, and, if left untreated, it can lead to permanent eye damage. Some will develop chlamydia pneumonia in the first three to four weeks of life. In men, if left untreated, an infection of the testicles called epididymitis develops, which often leads to prostate infections. Penicillin is not effective.
There are three species of Chlamydia that are of medical interest:
- C. trachomatis is transmitted sexually and is the one most prevalent of all sexually transmitted organisms, accounting for four million infections annually in the US. It is an unusual feature for one species to cause such a variety of clinically different diseases as this one does, but it is responsible for three categories of diseases: trachoma, a variety of sexually transmitted diseases, and lymphogranuloma venereum. Lymphogranuloma venereum (LGV) is sexually-transmitted and is caused by distinct chlamydial serotypes. A variety of nonspecific symptoms can occur in the early stage of the disease, followed by lesions on the skin and the genitals. Enlarged lymph nodes or buboes appear, then break and drain. There is often an accompanying fever, headache, nausea, and skin rash. If untreated, the disease can lead to permanent lymphatic or rectal blockage. The diseases are usually treated with sulfonamides, tetracyclines, and rifampin. Although it has been fading away in the US, except in gay men, it is now common in regions of Africa, Central America, and Asia, where it is of concern to visiting troops. C. trachomatis is the cause of trachoma, the single most important eye infection in the world, affecting over 600 million people worldwide and causing blindness in about 20 million of them. Infection typically starts with the upper eyelid and progresses to the conjunctiva (keratitis). Rubbing transfers the infection from one eye to the other, and the cycle begins again, leaving scarring that is prone to secondary infections in addition to blindness. Sexually transmitted diseases include conjunctivitis (passed to infants during birth), urethritis, cervicitis, pelvic inflammatory disease, gonnorhea, and inflammation of the Falopian tubes (salpingitis), that often leads to ectopic (tubal) pregnancies and infertility.
- C. psittacii causes psittacosis, or parrot fever. Its name is derived from the first isolation of the bacteria from the psittacine birds (parrots and parakeets). Today, the disease is also known as ‘ornithosis’ because it can infect birds and domesticated animals other than birds from the Psittacine family. Some birds that can infect humans are parakeets, parrots, pigeons, occasionally turkeys, ducks, geese, canaries, and once in a while the snowy egret, seagulls, and herons. Sometimes healthy birds carry the bacteria which are shed on their feathers and in their droppings – often for weeks or months. Stressed birds, as those kept in crowded containers, are more likely to shed the bacteria. The risk of infection is greater when the birds are kept indoors or in enclosed areas. The bacteria can be contracted through inhalation or from a bite or scratch. Early treatment with antibiotics reduces the fatality rate significantly.
- C. pneumoniae is implicated in heart disease and has been recognized in recent years as a significant cause of pneumonia infections around the world.