EFFECT OF SEMIANNUAL TREATMENTS OF IVERMECTIN ON THE PREVALENCE AND INTENSITY OF ONCHOCERCA-VOLVULUS SKIN INFECTION, OCULAR LESIONS, AND INFECTIVITY OF SIMULIUM-OCHRACEUM POPULATIONS IN SOUTHERN MEXICO

The effect of semiannual ivermectin treatment along with nodulectomy o n filarial transmission levels were estimated during the three dry sea sons of 1991-1993 in a hyperendemic village in southern Mexico. Parasi tologic and ophthalmologic examinations were carried out every six mon ths until five drug treatments were completed. Ivermectin mass treatme nt with a coverage of approximately 80% had a significant impact (P < 0.05) on the prevalence of skin infection and the mean microfilarial s kin density (CMFL), which were reduced 38% and 89%, respectively. A gr adual and significant (P < 0.05) decrease in the mean microfilariae nu mber in the anterior chamber of the eye and in corneal opacities was a lso observed as the CMFL was reduced. After three treatments, these we re reduced 84% and 69%, respectively. However, after two years of cont inuous intervention, no significant differences (P > 0.05) were observ ed in either the daily mean infective biting density and the daily mea n transmission potential. This was probably due to the remaining micro filarial load provided by the untreated resident population and migran t groups. On the whole, our results confirm both the efficacy of iverm ectin to alleviate the clinical manifestations of the disease and its minimal impact on Onchocerca volvulus transmission, and indicate the n eed both to achieve higher levels of drug coverage and to incorporate other measures to stop transmission until a macrofilaricide drug is fo und.