Chlamydia

An obligate intracellular parasite explains both the tropism and the silence

Chlamydia trachomatis cannot survive outside a host cell: it exists as an infectious elementary body that attaches to and enters columnar epithelium, then converts inside the cell to a metabolically active reticulate body that replicates before rupturing the cell to release new elementary bodies. This life cycle confines infection to columnar-lined sites (endocervix, urethra, rectum, conjunctiva and pharynx) rather than the squamous epithelium of the vagina, and because the intracellular damage is slow and the local inflammatory response is often mild, most infections cause few or no symptoms. This is the single fact that explains why chlamydia is the commonest bacterial STI in the UK and why screening, not symptom-triggered testing, drives detection.