Optimal strategies for controlling riverine Tsetse Flies using targets : a modelling study

CITATION: Vale, G. A., et al. 2015. Optimal strategies for controlling riverine Tsetse Flies using targets : a modelling study. PLoS Neglected Tropical Diseases, 9(3):e0003615. doi:10.1371/journal.pntd.0003615.The original publication is available at http://journals.plos.org/plosntdsBackground: Tsetse flies occur in much of sub-Saharan Africa where they transmit the trypanosomes that cause the diseases of sleeping sickness in humans and nagana in livestock. One of the most economical and effective methods of tsetse control is the use of insecticide-treated screens, called targets, that simulate hosts. Targets have been ~1m2, but recently it was shown that those tsetse that occupy riverine situations, and which are the main vectors of sleeping sickness, respond well to targets only ~0.06m2. The cheapness of these tiny targets suggests the need to reconsider what intensity and duration of target deployments comprise the most cost-effective strategy in various riverine habitats. Methodology/Principal Findings: A deterministic model, written in Excel spreadsheets and managed by Visual Basic for Applications, simulated the births, deaths and movement of tsetse confined to a strip of riverine vegetation composed of segments of habitat in which the tsetse population was either self-sustaining, or not sustainable unless supplemented by immigrants. Results suggested that in many situations the use of tiny targets at high density for just a few months per year would be the most cost-effective strategy for rapidly reducing tsetse densities by the ~90% expected to have a great impact on the incidence of sleeping sickness. Local elimination of tsetse becomes feasible when targets are deployed in isolated situations, or where the only invasion occurs from populations that are not self-sustaining. Conclusion/Significance: Seasonal use of tiny targets deserves field trials. The ability to recognise habitat that contains tsetse populations which are not self-sustaining could improve the planning of all methods of tsetse control, against any species, in riverine, savannah or forest situations. Criteria to assist such recognition are suggested. Author Summary: We employed a deterministic model to simulate the efficacy of various ways of using the tiny, ~0.06m2, insecticide-treated targets recently recommended as replacements for the larger, ~1m2, types previously used to control riverine species of tsetse fly, the main vectors of sleeping sickness in humans. Results suggested that in many situations the use of tiny targets at treble the normal density for a third of the normal time could be the most cost-effective strategy for rapidly reducing or eliminating tsetse populations, so helping with disease control. In deciding whether to aim for local control or elimination, and in planning the operations, it would be highly advantageous to distinguish those parts of the tsetse infestation that support self-sustaining populations, and those containing populations that cannot be sustained unless supplemented by immigrants. Sorts of information that can help to assess the type of sustainability in field habitats are identified. These findings can assist the planning of any method of tsetse control used against any species of tsetse, including those important as vectors of livestock disease.Publisher's versio