Despite a global decrease in incidence and mortality thanks to the implementation of integrated control measures, most of sub-Saharan Africa continues to carry a high share of the global malaria burden. Moreover, in some sub-Saharan countries there has been an increase in cases, even in presence of large-scale Long-Lasting Insecticide Net distribution (LLIN, the major vector control intervention), possibly associated with a shift towards exophilic malaria vector species and/or an increase of outdoor biting behavior. In Burkina Faso in particular, four major Anopheles vectors are responsible of most malaria burden: A. coluzzii, A. gambiae, A. arabiensis, and A. funestus. Their ecological features and genetic plasticity are major threats to an effective control of malaria in the country. Moreover, the decrease of LLIN effectiveness also due to resistance developed by malaria vectors against pyrethroid insecticides, the most important class of insecticides used to impregnate mosquito nets.
Data collected in the Burkinabe village of Goden during the rainy season 2011 by our research group show that the protective performance of LLINs can be weak despite the high coverage: low values of human blood index (5%) in mosquito vectors collected indicate a high risk of transmission.
We aim to analyze mosquitoes already available from a parallel survey conducted in a different village, to confirm the LLIN-induced ¿low HBI/high SR¿ scenario and thus provide a possible explanation of such phenomenon. To achieve this goal, we will: i) taxonomically identify malaria vectors to assess their resting behavior, ii) define their infectivity and feeding preferences, and thus their role in transmission, iii) determine the frequency of pyrethroid resistance alleles. Integrating ecology and epidemiology, we aim to give a wider perspective on factors influencing malaria transmission, useful for the implementation of efficient control strategies.
The proposed research is related to an emerging major issue on malaria control due to the reduced efficiency of LLINs in some hyperendemic sub-Saharan countries. It is reasonable to envisage that one of the major flaws in the efficacy of LLIN-prevention might be related to a rapid ecological adaptation of malaria vectors to such a strong selective pressure. In fact, an increase in frequency in insecticide resistance in mosquitoes has been reported after LLIN introduction (Czeher et al. 2008, Malar J., 7:189). Furthermore, resistant mosquitoes appear to be more infected by Plasmodium than susceptible ones, but data on A. gambiae are still contradictory (Traoré et al. 2019, Malar J., 18:165; Ibrahim et al. 2019, Malar J., 18:181) and a single evidence has been reported so far for A. funestus (Tchouakui et al. 2019, Sci Rep. 9: 5772). Unfortunately, data to establish if this phenomenon is occurring in Burkina Faso are still scarce for A. gambiae and yet unavailable for A. funestus. This study aims to fill this gap in knowledge on malaria epidemiology in Burkina Faso after LLIN introduction, also thanks to the availability of mosquitoes collected both indoors and outdoors.
The integration of data bridging ecology (i.e. resting beahviour, feeding preference) and epidemiology (i.e. infectivity status and insecticide resistance) will give a wider perspective on factors influencing malaria transmission risk, particularly outdoors, where malaria control strategies still await for implementation and optimization of efficient tools.