Onchocerciasis in Ecuador. I. Prevalence and distribution in the province of Esmeraldas.

In the province of Esmeraldas in Ecuador, 11 endemic foci of onchocerciasis were identified. The major focus, located on Rio Cayapas, consisted of 65 contiguous positive communities with an average infection rate of 51.1%. A distance-dependent characteristic of the onchocerciasis infection suggested that the transmission was centered principally in the areas near the head-waters of the river. This area, inhabited primarily by the indigenous tribe, Chachi, with an infection rate of 85%, was considered an area of hyperendemicity. Towards the river's mouth, where the majority of the inhabitants were Blacks, the rate of infection was 7%. The endemic focus located on Rio Santiago, populated entirely by Blacks and consisting of 17 contiguous positive communities, had an average infection rate of 18.8%. Again, the highest rate of infection, 33%, occurred in the upper reaches of the river. Resulting from the transient and migratory activity of some microfilariae-positive persons, 9 other isolated foci were found dispersed throughout the province. The infection rate of each focus was distinct, reflecting geographical location and ethnic composition. All foci other than the interior regions of Rio Cayapas were areas of hypoendemicity.