Effects of livestock management and insecticide treatment on the transmission and control of human malaria

This thesis aims to clarify the different effects of livestock on human malaria in areas where the disease is transmitted by zoophilic mosquito vectors, to understand under which circumstances livestock-based interventions could contribute to malaria control. Namely, the impact of livestock abundance, availability and insecticide treatment (lTL) were explored, by developing a comprehensive deterministic mathematical model and integrating it with data from Pakistan, where an ITL trial for malaria control has been performed, and from Ethiopia, where I conducted a field study to parameterize the model. The model allows explaining situations where livestock by itself can lead to an increase, decrease or no impact at all on malaria transmission, by combining the effects of livestock on decreasing the human blood index, while decreasing vector mortality and increasing vector density. The key explanatory factors are the: abundance and availability of livestock and human hosts, vector density in relation to the system's carrying capacity before livestock introduction, and time elapsed since livestock introduction. The overall findings indicate that ITL is likely to produce stronger decrease in malaria in settings with highly zoophilic vectors as in Asia, than in African settings with the more opportunistic vector An. arabiensis. Nevertheless, the results suggest that ITL is still likely to substantially decrease malaria incidence in the latter settings. The work highlights the importance of accounting for potential excito-repellency effects of the insecticide upon vectors, although only if excitorepellency is very strong would ITL become prejudicial. It is also important to understand the density-dependent regulation operating in the vector population, given its determinant effects upon the intervention outcome. It is hoped that this work may pave the way for the implementation of an ITL intervention trial in an African region with An. arabiensis where this strategy could contribute to the integrated control of malaria and livestock diseases.