Modeling the Control of Trypanosomiasis Using Trypanocides or Insecticide-Treated Livestock

<div><h3>Background</h3><p>In Uganda, Rhodesian sleeping sickness, caused by <em>Trypanosoma brucei rhodesiense</em>, and animal trypanosomiasis caused by <em>T. vivax</em> and <em>T. congolense</em>, are being controlled by treating cattle with trypanocides and/or insecticides. We used a mathematical model to identify treatment coverages required to break transmission when host populations consisted of various proportions of wild and domestic mammals, and reptiles.</p> <h3>Methodology/Principal Findings</h3><p>An <em>R</em>o model for trypanosomiasis was generalized to allow tsetse to feed off multiple host species. Assuming populations of cattle and humans only, pre-intervention <em>R</em>o values for <em>T. vivax</em>, <em>T. congolense</em>, and <em>T. brucei</em> were 388, 64 and 3, respectively. Treating cattle with trypanocides reduced <em>R</em>₀ for <em>T. brucei</em> to <1 if >65% of cattle were treated, <em>vs</em> 100% coverage necessary for <em>T. vivax</em> and <em>T. congolense</em>. The presence of wild mammalian hosts increased the coverage required and made control of <em>T. vivax</em> and <em>T. congolense</em> impossible. When tsetse fed only on cattle or humans, <em>R</em>₀ for <em>T. brucei</em> was <1 if 20% of cattle were treated with insecticide, compared to 55% for <em>T. congolense</em>. If wild mammalian hosts were also present, control of the two species was impossible if proportions of non-human bloodmeals from cattle were <40% or <70%, respectively. <em>R</em>₀ was <1 for <em>T. vivax</em> only when insecticide treatment led to reductions in the tsetse population. Under such circumstances <em>R</em>₀<1 for <em>T. brucei</em> and <em>T. congolense</em> if cattle make up 30% and 55%, respectively of the non-human tsetse bloodmeals, as long as all cattle are treated with insecticide.</p> <h3>Conclusions/Significance</h3><p>In settled areas of Uganda with few wild hosts, control of Rhodesian sleeping sickness is likely to be much more effectively controlled by treating cattle with insecticide than with trypanocides.</p>