Introduction
Development of disease
- Trachoma is a conjunctivitis caused by repeated episodes of ocular infection with Chlamydia trachomatis.
- Most transmission occurs in young children who directly share infected eye and nose secretions with others.
- Children have more frequent episodes of reinfection than adults and have longer lasting episodes of clinical disease.
- If there is no further transmission the conjunctival follicles will resolve slowly, usually in 3 to 6 months.
- People with severe trachoma, trichiasis and corneal opacity leading to blindness may have had up to 150 episodes of infection especially during childhood.
- As an immune mediated disease, trachoma forms follicles (germinal centres) in the upper tarsal conjunctiva. The follicles are a delayed type of hypersensitivity reaction following repeated episodes of reinfection.
- This in turn leads to increasingly severe inflammation that progresses to scarring of the upper tarsal conjunctiva.
- Trichiasis, in-turned eyelashes, develops when scarring distorts the upper eyelid and causes one or more lashes to rub on the cornea that then becomes scarred.
- The ensuing blindness is essentially irreversible.