8.7 Control of Parasitoses

Major projects for the control of parasitic diseases are planned and supervised by the world Health Organisation (WHO), which covers environmental, public health and similar general scientific aspects. Measures directed against the pathogen itself are mostly combined with others against the vector or intermediate host. For relevant decisions, first the general situation, i.e. the prevalence and incidence of the disease, and the population at risk have to be analysed.

During the preparation phase, the scientist has to concentrate on the methods intended to determine the efficacy of the proposed measures. For the evaluation of efficacy, sensitive and specific parameters are necessary (Box 2.1, page 28). Desired or undesired trends should be recognized as early as possible to save time and funds. Incidence and prevalence change over years. They are specific but less sensitive. The decrease of the population density of a vector or intermediate host can immediately be observed. Such parameters are sensitive, but less specific.

The control, for example, of mosquito larvae that do not carry the parasite stages needs an identification chain that has to establish that the corresponding imagoes are indeed the transmitting vectors. Subspecies or cyto-taxonomic species living under different ecological conditions might be important. The various types of an insect species usually go through seasonal population shifts, which must be permanently supervised. Pilot projects will test methods by trial and error in limited areas

During the subsequent attack phase, incidence should decrease until a critical value of transmission potential is achieved. Thereafter, measures have to be intensified until the critical value of incidence is achieved in order to establish that transmission is interrupted. During the following consolidation phase, the disease can no longer be found by the methods previously used. The disease is under control and in the following maintenance phase, the population at risk has to be supervised in order to prevent reinvasion from neighbouring regions. In most cases, the project area should obviously be expanded to adjacent sites.

In addition to the calculation of rentability (the resultant economic advance should support not only the ongoing costs of maintenance), employed staff have to be retrained for modified tasks. Socio-economic improvements in clothing, footwear, living comfort and hygiene should minimize the population at risk. The improvement of the global burden of disease based on the disability adjusted life years (DALYs, see chapter 8.4) is the standard for success.

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