The population dynamics of Onchocerca volvulus in the human host

Abstract

The quantitative aspects of onchocerciasis that focus on the relationship between the number of adult female Onchocerca volvulus in the human host, the total numbers of microfilariae (mfs) in the body at any one time, and the numbers of infective larvae (L3) to which a person is exposed over time, have received little attention. This paper attempts to investigate the problem from three starting points:--(a) using the numbers of palpable nodules to estimate the numbers of productive female worms in the body; (b) using the concentrations of mfs in skin snips to estimate the total load of mfs in the body; and (c) using the Annual Transmission Potential to estimate the numbers of L3 developing to productive female maturity. By analysing published and unpublished data relating to the forest and savanna zones of West Africa, these three approaches indicate that a relatively large proportion of adult female worms lie deep in the body and are impalpable from the surface. They also provide numerical results, of the same order to magnitude, which can be linked to provide estimates of the total numbers of adult female worms and mfs in the bodies of persons with infections of different intensities.