Do the LLINs really protect from malaria at community level in areas of high transmission?

Long Lasting Insecticidal Nets (LLINs) are among the most effective strategies in malaria vector control, halving the population at risk in sub-Saharan Africa since 2010.Despite this success, in some hyperendemic African countries, such as Burkina Faso,the annual incidence and the entomological infection rates are still very high. Evidencefrom a hyperendemic LLIN-protected village of Burkina Faso (Goden, Ouagadougouarea) in 2011-2012 showed high Sporozoite Rates in major vector species (SR>7%), despite very low Human Blood Index (HBI<16%). We here report a similar picture fromanother LLIN-protected village in the same area (Koubri), where Anopheles funestusshows consistently high SR (8.6%) associated to a very low HBI (5.8%) associated toa strong exophilic behavior, suggesting again lack of community level protection despite massive LLIN implementation. We thus carried out a second entomological survey in Goden in 2015 by Human Landing Catches at three different time points duringthe night (21-22; 00-01; 03-04) and collected a total of 1,955 Anopheles gambiae complexspecimens (A. coluzzii 55%, A. arabiensis 44%, A. gambiae 1%, without significant differences indoors vs outdoor, nor among time points). The median number of host-seekingmosquitoes/hour/person was 23.5 and the SR among the 692 specimens analysed sofar was 6.2% (without significant differences in indoors vs. outdoors), correspondingto an entomological inoculation rate in equal to 1.46 infective bites/hour. Overall, theseresults highlight that, despite the large-scale usage of LLINs in the area since 2010, themosquito population is still present at high densities and highly infected, probably asa consequence of shifting in biting behaviour of vector species. This leads to a non-negligible risk of malaria transmission to people either sleeping unprotected by a bednetindoors or exposed to mosquito bites outdoors and may explain the reduced effect ofLLIN implementation in hyperendemic regions of sub-Saharan Africa.