Evidence of low community level protection from malaria transmission despite High LLIN-coverage in a village of Burkina Faso

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 the annual incidence and the entomological infection rates are still very high. In Burkina Faso the raising of LLIN coverage from 20% to 70% led to a significant reduction of malaria prevalence, without major effects on annual incidence. Evidence from a hyperendemic LLIN-protected village of Burkina Faso (Goden, Ouagadougou area) in 2011 and 2012 showed high Sporozoite Rates (SR>7%) in major vector species, despite Human Blood Indexes (HBI<16%), raising the need of deeper investigation to assess the potential risk of transmission to unprotected people in the area. We thus carried out an entomological survey in the village in November 2015 by Human Landing Catches at three different time points (21-22; 00-01; 03-04) in order to estimate the Entomological Inoculation Rate (EIR). A total of 1,955 Anopheles gambiae complex specimens was collected (A. coluzzii 55%, A. arabiensis 44%, A. gambiae 1%, without significant differences between in-outdoors collections and among the three time points) corresponding to a median number of 23.5 host-seeking mosquitoes/hour/person. Among 692 specimens analysed so far, the SR was 6.2%, without significant differences in indoor vs. outdoor collected specimens. Therefore, the entomological inoculation rate is equal to 1.46 infective bites/hour.This result highlights that, despite the large-scale usage of LLINs in the village since 2010, the mosquito population in the area is still highly infected and present at high densities, leading to a non-negligible risk of malaria transmission both to people either sleeping unprotected by a bednet indoors or exposed to mosquito bites outdoors.