Both doxycycline and placebo will be administered under supervision (directly observed treatment) for 6 weeks. The first dose of doxycycline (two 100 mg tablets for those over 50kg body weight and one 100 mg tablets for those between 40 and 50 kg body weight) or placebo will be given after all the investigations have been completed and informed consent has been obtained and the patient has been initiated into the programme of basic hygiene. Patients will be encouraged to eat before swallowing the tablets whole with a glass of water. Vomited doses will be replaced.