Assessment of the density of infection with onchocerciasis and the probable level of safety from its ocular complications

Abstract

Summary 1. (1) A method of assessing the density of infection with onchocerciasis in an individual, called the Individual Density Figure, is given, and the factors considered in devising the method discussed in detail. 2. (2) The method is based on the known anatomical distribution of the mf. population, and not on mf. counts, which are shown to be subject to wide variations in the same site in untreated cases from day to day. 3. (3) A method of assessing the density of infection with onchocerciasis in a community, called the Density Quotient, and based on the same principle, is also given, and discussed in detail. 4. (4) In the individual, conjunctival biopsies and skin biopsies from the neck, chest, thigh, and calf are taken; in subjects in a random sample within a community, conjunctival biopsies and skin biopsies from the neck and calf only. A system of scoring is explained for each. 5. (5) The number of people blinded by onchocerciasis and the average number of onchocercomas per person are factors discarded in assessing the degree of infection. 6. (6) It is suggested that a safe level of infection exists, at which there is no risk of blindness; this level is measurable by the methods recommended. It is this level at which all therapeutic and control measures should aim.