Monitoring malaria vector densities and behaviours in Tanzania

Malaria remains the most important parasite-related public health problem globally, with the majority of burden occurring in sub Saharan Africa. Increased political and financial support has resulted in rapid scale up of malaria prevention measures, so that disease burden has been substantially reduced in many African countries. However, behavioural change by malaria vector populations, so that a greater proportion of human exposure to bites occurs outdoors, threatens to undermine the impact of malaria control with existing front line interventions such as insecticide treated nets (ITNs) and indoors residual spraying (IRS) because both act indoors. Also, progress towards lower transmission levels poses substantive entomological monitoring challenges because most standard methods fail to detect low levels of vector density and malaria transmission. The overall goal of this study was to enhance understanding of the potential and limitations of ITNs for reducing malaria transmission by outdoor biting mosquitoes, and to develop a safe, sensitive, practical and effective malaria vector surveillance tool that enables sustained entomologic monitoring of intervention impact. An existing mathematical model was adapted to examine the possibility that ITNs can achieve community suppression of malaria transmission exposure, even when mosquitoes avoid them by feeding on people while they are outdoors. Simulations indicated that ITNs may provide useful levels of community suppression of malaria transmission, even when outdoor biting rates exceed indoor biting rates and slightly more than half of bites occurred at times and places when using ITNs is not feasible. This suggests that ITNs should not be deprioritized as a malaria control tool simply because local vector species prefer to feed outdoors. Nevertheless, complementary interventions that target outdoor- and early-biting mosquitoes should be prioritized, especially for going beyond malaria control to achieve elimination. Cross over and Latin Squares experimental designs were used to compare the sensitivity of multiple trapping techniques for catching malaria vectors, under conditions of both high and low mosquito density, in rural Kilombero and urban Dar es Salaam, respectively. A new tent style trapping device called the Ifakara Tent Trap was successfully developed and proved to be safe and more efficacious than any other commonly used alternative to human landing catch for catching Anopheles gambiae s.l. in the low transmission setting of urban Dar es Salaam. Its sampling efficiency appeared to be independent of vector density in a rural setting with high mosquito abundance but increased as mosquito densities decreased in an urban area of low mosquito density where it exceeded that of HLC at lowest densities. This density- dependence of the trap implies that this tool may have particular potential for monitoring malaria in low transmission settings. It was also demonstrated to be effective when used by unsupervised community members under programmatic conditions and it is currently the only technique used for routine adult mosquito surveillance by the Urban Malaria Control Programme of Dar es Salaam. However, it cannot be used to determine how bites upon humans are distributed between indoor and outdoor exposure components