Evaluation of the impact of long lasting insecticidal nets (llins) on malaria transmission in Burkina Faso

Background. Malaria is the first parasitic disease in the world for mortality and morbidity, recording the highest prevalence in sub-Saharan Africa with about 445.000 deaths and 2 million of new cases every year. LLINs are among the most effective strategies in malaria control. LLIN three-year distribution campaigns, recommended by the WHO, prevented 68% of the malaria cases in Africa, thanks to the combination of physical barrier and insecticidal activity against vectors. Despite this success, the effectiveness of LLINs in sub-Saharan Africa seems to be heterogeneous, since in some hyperendemic countries like Burkina Faso (where the LLIN reached 70%) the malaria incidence and the entomological infection rates are still very high. According to this scenario, from an entomological survey conducted in the rural village of Goden (Burkina Faso) in 2011 - i.e one year after the first LLINs distribution campaign - we detected unexpected high Plasmodium Sporozoite Rates (SR) of 7.1% in malaria vectors. This suggests a partial protective effect of LLINs in reducing transmission at population level in this area. Objectives: we aim to evaluate the impact of LLINs on malaria transmission in Burkina Faso, taking the opportunity of a new distribution of nets in 2019 considering two areas differing for climate and vector species composition: Goden and Banfora. To this purpose, through the period 2019-2021, several endpoints will be monitored in the villages: entomological parameters (SR, human biting rates, insecticide resistance), local malaria clinical information and bednet physic conditions. Moreover, a systematic review will be conducted in order to investigate, at larger scale, possible correlation between malaria annual incidence and the performance of different LLIN brands according to their local usage in the country. Preliminary and expected results. Data on mosquitoes collected in 2015 in Goden shows a rate of 1.5 infective bites/person/night both inside and outside houses, confirming partial protective effect of LLINs. Thus, the three-year entomological survey planned in two representative settings, as well as the information gathered from meta-analysis on different LLIN brands distributed in the country, will allow to measure the LLIN protective effect at individual and community level and to point out possible limits in durability (physical integrity, wash resistance, insecticide content) of LLINs used in Burkina Faso. Future perspectives. This study could help to enlighten the reasons of LLINs reduced efficacy in Burkina Faso and possibly in other countries of sub-Saharan Africa where this tool seems to be ineffective, ultimately adding information of major importance in the planning of appropriate country-based malaria control strategies.