Which Chlamydia trachomatis serovars are responsible for endemic trachoma (TF and TI stages)?

Explanation

## Chlamydia trachomatis Serovars in Trachoma **Key Point:** Endemic trachoma (active infection and trichiasis/entropion stages) is caused exclusively by serovars A, B, Ba, and C of Chlamydia trachomatis. ### Serovar Classification and Disease Association | Serovars | Disease Type | Clinical Features | |----------|--------------|-------------------| | A, B, Ba, C | Endemic trachoma (TF, TI) | Chronic keratoconjunctivitis, scarring, blindness | | D–K | Ocular and genital infection | Acute follicular conjunctivitis, urethritis | | L1, L2, L3 | Lymphogranuloma venereum | Systemic lymphadenopathy, proctocolitis | **High-Yield:** Serovars A, B, Ba, and C are neurotropic and cause chronic, recurrent infection leading to scarring and blindness. This is the leading preventable cause of blindness worldwide, particularly in resource-limited settings in Africa, the Middle East, and South Asia. **Clinical Pearl:** The WHO simplified grading uses TF (trachomatous inflammation–follicular) and TI (trachomatous inflammation–intense) to identify active infection in endemic areas. Only serovars A–C cause this chronic endemic form. **Mnemonic:** **ABC** for endemic trachoma serovars — **A, B, Ba, C** (remember "ABC" + "Ba" as a variant of B).