Epidemiological impact of vector control. II. Changes in ocular onchocerciasis

The impact of 10-11 years of successful vector control on ocular onchocerciasis was evaluated in the population of 13 villages in the central part of the Onchocerciasis Control Programme area. The prevalence of ocular microfilariae was found to have reduced remarkably and loads over 20 microfilariae in the anterior chamber of the eye or the cornea which was rampant before the start of vector control, were rare. Whilst limited change in the age specific prevalence of lesions of the posterior segment of the eye was recorded, significant reduction in the prevalence of lesions of the anterior segment of the eye was found. The small decrease in the age specific prevalence of lesions of the posterior segment of the eye was partly explained by a reduced occurrence of the type of lesions of the anterior segment of the eye which previously obstructed the effective view of the fundus during examination. The prevalence of blindness was found to have reduced by 40% and onchocercal blindness was no longer found below the age of 20 years. It was concluded that 10-11 years of successful vector control has effectively reduced the incidence of onchocercal eye lesions, the deterioration of the existing eye lesions and the risk of developing an onchocercal eye lesion as well as going blind to virtually nil.