Effects of onchoceriasis on settlement in the Middle Hawal Valley, Nigeria.

Eight lowland villages in which onchocerciasis is hyperendemic are compared with two upland (low prevalence) control villages in the middle Hawal valley, Nigeria. Detailed demographic data from the hyperendemic villages and from the control villages are analysed. The population was found to be more mobile in the lowland zone, which is also the zone of village desertion. Variables influencing the probability of village abandonment are discussed. It is suggested that onchocerciasis is only a part of a complex of desertion, though probably the most important single element. Particularly in association with remoteness, itself related to onchocerciasis and its troublesome vector, onchocerciasis has been instrumental in depopulating riverain areas and continues to perpetuate their unattractiveness.