Evaluating the potential for the development of mosquito behavioural avoidance to compromise Insecticide-Treated Nets in southern Tanzania
Background: The mass distribution of Long lasting Insecticide Treated Nets (LLINs) and Indoor Residual Spraying (IRS) programmes throughout sub-Saharan Africa have generated massive reductions in malaria transmission. The success of these strategies lie in their exploitation of a key vulnerability of the Anopheles mosquitoes that transmit malaria: their strong behavioural predisposition to feed at night when people are sleeping, and rest inside their houses. LLINs and IRS continue to prove highly successful for targeting mosquitoes that feed and rest indoors, but are less effective against mosquitoes with more flexible feeding and resting behavior. Consequently with the expansion of LLIN and IRS programmes, there has been a substantial ecological shift in the composition of mosquito vectors from endophilic species such as An. gambiae s.s., towards those such as An. arabiensis that have more variable feeding and resting behaviours. An. arabiensis can avoid contact with insecticides by feeding on other animal species, biting and resting outdoors and/or earlier in the evening. In recent years, in the Kilombero Valley of Tanzania, the proportion of malaria transmission due to An. arabiensis has increased significantly and it now dominates transmission. There is growing evidence that An. arabiensis are capable of modifying their behaviour in the presence of vector control measures.
About this Project: In view of the potentially devastating epidemiological consequences of the development of behavioural avoidance strategies within mosquito vector populations, we conduct an in-depth investigation of the potential for this phenomenon to arise within the major malaria vector An. arabiensis in Tanzania, and evaluate its potential impact on the long-term sustainability of vector control measures. Working in four villages within the Kilombero Valley of Tanzania, namely Lupiro, Kidugalo, Minepa and Sagamaganga where malaria transmission is now dominated by An. arabiensis, we conduct detailed entomological investigations. Longitudinal surveillance of mosquito vector behaviours was established over a 5 year period (2011-2016) during which LLIN coverage levels are expected to grow to near 100% to test for the emergence of behavioural shifts in the timing and location of mosquito feeding and resting that may reduce the effectiveness of vector control. In parallel, detailed ecological monitoring is conducted to identify the contribution of environmental factors to variation to these mosquito behaviors (e.g. inside versus outside, early or late evening biting), and evaluate their implications for human exposure risk in different settings.