The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal

Abstract

The implementation of long-lasting insecticidal-treated bed nets (LLINs) has contributed to halving the mortality rate due to malaria since 2000 in sub-Saharan Africa. These tools are highly effective against indoor-feeding malaria vectors. Thus, to achieve the World Health Assembly's new target to reduce the burden of malaria over the next 15 years by 90%, it is necessary to understand how the spatiotemporal dynamics of malaria vectors and human exposure to bites is modified in the context of scaling up global efforts to control malaria transmission. This study was conducted in Dielmo, a Senegalese village, after the introduction of LLINs and two rounds of LLINs renewals. Data analysis showed that implementation of LLINs correlated with a significant decrease in the biting densities of the main malaria vectors, s.l. and, reducing malaria transmission. Other environment factors likely contributed to the decrease in , but this trend was enhanced with the introduction of LLINs. The bulk of bites occurred during sleeping hours, but the residual vector populations of s.l. and had an increased propensity to bite outdoors, so a risk of infectious bites remained for LLINs users. These results highlight the need to increase the level and correct use of LLINs and to combine this intervention with complementary control measures against residual exposure, such as spatial repellents and larval source management, to achieve the goal of eliminating malaria transmission.

Anopheles arabiensis and Anopheles funestus biting patterns in Dielmo, an area of low level exposure to malaria vectors

“…During the night, the peak of hourly aggressiveness observed did not change compared to a previous study in Dielmo and remains con ned to the second part of the night [7]. This indicates that the population could be protected while resting indoor, as the peaks observed during the night correspond to moments when the population is asleep [7], with a relatively high compliance rate in the use of LLINs [4], unlike the peak that occurs during the day, when people are awake and remained unprotected by the LLINs. Thus, in areas striving to eliminate malaria, more attention should be paid to the possible Anopheles morning biting activity which essentially takes place indoors and throughout the year, which could maintain residual levels of Plasmodium transmission.…”

“…In Dielmo, the introduction of a signi cant healthcare system allowing for rapid diagnosis and malaria case management [28], combined with close entomological monitoring are used to detect and/or prevent outbreaks that can result from this low level of transmission. The increase in Anopheles outdoor biting which was observed after the implementation of LLINs or indoor residual spraying (IRS) in endemic malaria areas [6,7,29], could also sustain the residual transmission of malaria. Indeed, the shift of the Anopheles to outdoor biting, combined with changing human behavior in Dielmo marked by increased outdoor nocturnal activity due to rural electri cation could sustainably maintain residual outdoor exposure to vector bites and the occurrence of malaria outbreaks [3].Therefore, controlling outdoor exposure is the current challenge facing malaria control programmes.…”

“…Indeed, it is well known that most of the e cient vectors of malaria in endemic areas have developed particular behaviour enabling them to avoid insecticide-treated nets insecticide and to feed safely on the human population [5]. This avoidance of LLINs by Anopheles is currently marked by signi cant outdoor feeding after the introduction of bed nets in some endemic areas [6,7]. In addition to increased outdoor biting, Anopheles may adapt their biting time to speci c periods during which the LLINs may not be used by the population.…”

Another challenge in malaria elimination efforts: the increase of malaria among adults after the implementation of long-lasting insecticide-treated nets (LLINs) in Dielmo, Senegal

“…This outdoor behaviour has been shown previously in some studies as malaria risk factor [ 2 , 8 ]. In Dielmo after the implementation of LLINs, the residual vector populations of Anopheles gambiae sensu lato and Anopheles funestus had an increased preference to bite outdoors [ 21 ]; thus, spending time out lately at night remained malaria risk factor in this village [ 9 ]. Another explanation of the shift of malaria risk age was that children often slept under LLINs with their mother, while adult men specially slept later and not often used their nets [ 22 ].…”

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

“…Other important advantages of LLINS include reduced consumption of insecticides and insecticide released into the environment because they do not need retreatment [85]. The efficacy of LLINs is closely related to the molecules used (the choice depends on the presence or absence of its resistance) [90], and their correct use may enhance their efficiency [91]. In a study, the use of LLINs led to a dramatic reduction (97%) in the prevalence of malaria compared to a group of LLIN non-users [92].…”