Eligible participants will complete a 6-month Observation Phase, followed by a 24-month Treatment Phase, followed by an End of Study Visit. Eligible participants will be randomized at Month 6 in a 1:1 ratio to either ORACEA (40 mg doxycycline) or placebo capsule to be taken once-daily for 24 months. Over the course of the 31-month study, a total of 9 clinic visits and 3 telephone calls are required.