Onchocerciasis in Chiapas, Mexico

Abstract

Onchocerciasis (river blindness) is a serious health problem in Latin America. The most heavily infected region in Mexico is in the Sierra Madre de Chiapas. Early in the twentieth century, agricultural settlements expanded into this area and encroached onto an ecological zone suitable for the transmission of onchocerciasis. The disease has stabilized in numbers infected and extent, but it remains a chronic health problem. The pattern of the disease here demonstrates the dynamic relationship among population movement, landscape change, and disease diffusion. ONCHOCERCIASIS, or river blindness, is commonly associated with Africa (Hunter 1966), but the disease also affects an estimated 100,000 persons in Latin America, with clusters of incidence in Mexico, Gua- temala, Ecuador, Brazil, Colombia, and Venezuela (Shelley 1988). The disease was probably transmitted from Africa by the slave trade and established itself in Latin America in zones with appropriate ecological conditions (Ruiz Reyes 1952). This article examines the coevolution of onchocerciasis and a regional landscape in Mexico. The underlying components that help define the onchocerciasis system there are linked to population mobility and land- scape change. Both these variables have placed people, parasite, and disease vector together in time and space. Onchocerciasis is a disease system involving the filarial worm Onchocerca volvulus, a Simulium or black fly, and a human host. The black fly breeds in streams: hence the common name of the disease, river blindness. Various stages in the life of the parasite are carried in both black fly and human. The human is the definitive host; the black fly is only an intermediate part of the disease system. Two stages of the parasite, adult worm and offspring, occur in the skin and muscle tissue of an infected human. The male and female adult worms live together in a mass known as a worm nodule. Some lie deep in muscle tissue, but others are superficial and palpable, especially in the scalp. The female worms are viviparous, continually bringing forth live offspring known as microfilaria. They may live as long as two years in a human host.