## Causative Agent of Trachoma **Key Point:** Chlamydia trachomatis serovars A, B, Ba, and C are the exclusive causative agents of trachoma, the leading infectious cause of blindness worldwide. ### Organism Characteristics **High-Yield:** Chlamydia trachomatis is an obligate intracellular gram-negative bacterium that exists in two forms: - Elementary bodies (EB): infectious, metabolically inert - Reticulate bodies (RB): metabolically active, non-infectious ### Serovar Classification | Serovars | Disease | Geographic Pattern | | --- | --- | --- | | A, B, Ba, C | Trachoma (endemic) | Africa, Asia, Middle East, Latin America | | D–K | Inclusion conjunctivitis, urethritis | Sexually transmitted | | L1, L2, L3 | Lymphogranuloma venereum | Sexually transmitted | ### Clinical Significance in Trachoma **Clinical Pearl:** Serovars A and B cause more severe, recurrent infections and are associated with earlier onset of trichiasis and corneal scarring compared to serovars C and Ba. **Mnemonic:** **TrachOma = Obligate intracellular** — remember that Chlamydia cannot be cultured on standard media and requires special cell culture or nucleic acid amplification tests (NAAT) for diagnosis. ### Pathophysiology 1. Infection of tarsal conjunctiva → chronic inflammation 2. Repeated reinfection (especially in endemic areas with poor sanitation) 3. Fibrosis and scarring → entropion, trichiasis, pannus formation 4. Progressive corneal opacity and blindness if untreated **Key Point:** Trachoma is preventable and treatable with azithromycin (single-dose 20 mg/kg) or tetracycline eye ointment, making it a public health priority in endemic regions.
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