Trachoma, caused by particular serovars of Chlamydia trachomatis, is the leading infectious cause of blindness. Infection is transmitted within ocular and nasal secretions that are passed from person to person on fingers, fomites (such as clothing) and eye-seeking flies (particularly Musca sorbens). Ophthalmic infection is associated with an inflammatory conjunctivitis known as “active trachoma”. Repeated episodes of active trachoma can scar the eyelids. In some individuals this leads to trachomatous trichiasis (TT), in which one or more eyelashes on the upper eyelid touch the eye. TT is extremely painful. It can be corrected surgically, but, if left untreated, may lead to corneal opacification, resulting in vision impairment and blindness.