RESUMO
The prevalence of onchocerciasis infection was determined in communities on 7 rivers located in the northern area of the canton San Lorenzo, province of Esmeraldas. Diagnosis of the infection was obtained by skin biopsies and recombinant-antigen based-serology. No evidence of infection was detected in 9 communities studied along the Rio Mataje, which forms the frontier between Ecuador and Colombia, nor in 10 adjacent communities located on 5 interior rivers. Evidence for Onchocerca volvulus infection was found in 4 communities on the Rio Tululvi with the following prevalence: La Boca (3,5 per cent by biopsy and 3,9 per cent by serology), Guayabal (9,1 per cent by both biopsy and serology), La Ceiva (51,5 per cent by biopsy and 53 per cent by serology), and Salidero (4 per cent by biopsy and 7,7 per cent by serology). A few individuals in these communities were seropositive for O. volvulus in the absence of detectable dermal microfilariae: these might harbor very light or prepatent infections. No clinical disease attributable to onchocerciasis was found. The infected communities will be included in the ivermectin-based National Control Program for the disease, with no evidence of the infection having extended north of the Ecuadorian-Colombian border.