It has three medically important species. They are all obligate intracellular microbes and are known to produce intracytoplasmic inclusions by which they are diagnosed in smears. They are Gram negative but stain poorly with the Gram stain hence Giemsa, Castaneda or Macchiavello stains are used. Two different forms are seen in the body - elementary body and reticulate body. The elementary body is a metabolically inactive, infectious particle which enters the cell, becomes metabolically active and divides into daughter cells to form the reticulate body.
C.trachomatis: It is the most common cause of STD in the USA. It causes urethritis, inclusion conjunctivitis, trachoma, lymphogranuloma venereum (LGV) and pneumonia. It presents in males as urethritis, epididymitis and proctitis. In females, it presents as urethritis, cervicitis, vaginitis, salpingitis and infertility from tubal scarring of the fallopian tube. Infants can acquire conjunctivitis during passage through the birth canal.
Trachoma is a preventable cause of blindness. It is a chronic keratoconjunctivitis with corneal scarring. LGV is caused by C.trachomatis serovars L1 to L3. It presents as a unilateral, tender inguinal or femoral lymphadenopathy (bubo) accompanied by genital papule or ulcer, proctocolitis with blood and mucus discharge from the rectum often confused clinically with IBD (inflammatory bowel disease) and draining sinuses and fistulae.
Reiiter’s Syndrome is a “reactive” arthritis presenting with arthritis, urethritis and conjunctivitis in patients having genitourinary or gastrointestinal infections caused by Chlamydia, Salmonella, Shigella or Campylobacter bacteria. Remember that it is not directly due to infection but from an immunological response as a result of the primary infection.
C.pneumoniae: It causes a community acquired atypical pneumonia. Typically presents as cough with laryngitis, bronchitis,runny nose and other upper respiratory symptoms. It is usually mild but complications like encephalitis and myocarditis can occur. It can cause severe exacerbation of asthma in susceptible individuals. Interestingly it has been strongly associated with the pathogenesis of atherosclerosis and plaque buildup in arteries.
C.psittaci: Infection is acquired from birds such as parrots, pigeons and poultry. It presents as an influenza like illness, pneumonia, septicaemia or meningoencephalitis.
Tissue scrapings or discharge can be sampled for diagnosis. Intracytoplasmic inclusions stain blue with castaneda, red with Machiavello, purple or blue with Giemsa. Smears can also be stained with fluorescein isothiocyanate labelled antibodies (immunofluorescence) or detected by DNA probe hybridization. ELISA or PCR are other commonly employed techniques. LGV and C.trachomatis can be detected using complement fixation test. Cell culture or yolk sac culture can be done for isolation of organisms, it is not needed for clinical diagnosis though. In culture, C.trachomatis forms glycogen containing inclusions that stain brown with iodine while C.pneumoniae and C.psittaci inclusions lack glycogen so do not stain with iodine.
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