The application of a quantitative approach to the assessment of the relative importance of vector and soil transmitted diseases in Ghana

The vector and soil transmitted parasitic infections produce a highly diverse group of diseases in terms of the importance of their impact upon human populations and in terms of the control methods that might limit that impact. In Ghana a method was developed for quantitatively assessing the relative importance of different disease problems by estimating the amount of healthy life lost through illness, disability and death as a result of each disease. The quantitative assessment is derived from information on incidence rate, case fatality rate and the extent and duration of disability produced by the disease. The method may be used to help decide the priorities for the allocation of resources to alternative procedures or programmes by calculating the amount of healthy days of life which may be saved by different approaches and then relating these savings to the costs of the approaches. Each of the vector and soil transmitted parasitic diseases in Ghana had special characteristics that influenced the estimates of their relative importance. Attribution of death due to malaria posed special problems, but even with the most conservative estimate malaria was the single most important cause of loss of healthy life of all diseases in Ghana. For schistosomiasis there is such great uncertainty concerning how much disability or mortality that results from infection that the relative importance of schistosomiasis could not be usefully estimated; thus research into the extent of disability and death caused by schistosomiasis should have a very high priority if rational allocation of resources for its control is to be achieved. Onchocerciasis, though not generally considered an important cause of mortality, is an important cause of chronic severe disability. The importance of ascariasis and hookworm remain uncertain both because of the lack of information as to the extent of disability and mortality that they produce and the lack of data in Ghana as to their prevalence and intensity of infection. Guinea worm was of little importance from the national point of view, but was highly important in focal areas. Trypanosomiasis would appear to be of minor importance because its incidence was quite low, but for an epidemic disease such as trypanosomiasis the importance must be estimated based on what would occur if there were not effective surveillance and control methods. Diverse though this group of parasitic diseases is a common thesis is that each has been relatively neglected in relation to its importance and for each a considerable reduction in loss of healthy life should be achievable at reasonable cost.