Baseline entomologic data on malaria transmission in prelude to an indoor residual spraying intervention in the regions of Alibori and Donga, Northern Benin, West Africa

Abstract

BackgroundDespite the success of indoor residual insecticide spraying (IRS) in Africa, particularly in Benin, some gaps of information need to be filled to optimize the effectiveness of this intervention in the perspective of the country’s effort to eliminate malaria. In anticipation to the 2018 IRS campaign in two targeted regions of northern Benin, this study aimed, to collect baseline information on vector composition, spatio-temporal variation and peak malaria transmission in the Alibori and Donga, two targeted regions of northern Benin. Information collected will help to better plan the implementation and later on the impact assessment of this IRS campaign.MethodsThe study was carried out in four districts of the two IRS targeted regions of northern Benin. Human landing catches and pyrethrum spray catches protocols were used to assess the biting rate (HBR) and, biting/resting behaviour of malaria vector populations. After morphological identification of collected Anopheles, the heads and thoraxes of Anopheles gambiae sensu lato (s.l.) were analysed by the ELISA CSP tests to estimate the sporozoite index (SI). The entomological inoculation rate was calculated as the product of mosquito biting rate (HBR) and the SI.ResultsThe biting rates of An. gambiae s.l., the major vector in this study sites, varied significantly from region to region. It was higher: in rural than in urban areas, in rainy season than in dry season, indoors than outdoors. Overall, SI was comparable between sites. The highest EIRs were observed in the Donga region (16.84 infectious bites/man/month in Djougou district and 17.64 infectious bites/man/month in Copargo district) and the lowest in the Alibori region (10.74 infectious bites/man/month at Kandi district and 11.04 infectious bites/man/month at Gogounou district).ConclusionThis study showed the heterogeneous and various nature of malaria epidemiology in Northern Benin. Indeed, the epidemiological profile of malaria transmission in the Alibori and Donga regions is made of a single season of transmission interrupted by a dry season. This period of transmission is relatively longer in Donga region than in Alibori. This information can be used to guide the extension of IRS in the Alibori and in the Donga, by primarily targeting areas with short periods of transmission, and easy to cover.

Indoor and outdoor malaria transmission in two ecological settings in rural Mali: Implications for vector control

“…Such an observation was also made in Equatorial Guinea [32,[37][38][39][40]. However, recent data from Benin reported higher HBRs indoors than outdoors [36].…”

“…This could be due to the side effect of ongoing control measures like LLINs in these places as An. gambiae s.l., which were known to be more endophagic than exophagic [36]. Indeed, several studies have shown changing its biting and resting behavior from indoors to outdoors when LLINS were widely used in an area.…”

“…is known to be anthropophagic and endophilic but is becoming more exophilic and humans are staying outside houses longer and are bitten before going under mosquito nets. Other environmental factors, especially elevated ambient temperature, cause people to sleep with no protection against mosquitoes' biting [36] or outdoors. In fact, several studies reported a high outdoor transmission rate [32,37,46].…”

Assessment of novel Lehmann’s Funnel Entry Trap prototypes performance to control malaria mosquito populations

“…Female mosquitoes seek blood meals late at night in human dwellings [6][7][8], where they are vulnerable. Although malaria is mostly transmitted indoors, some studies in East and West Africa have shown malaria transmission occurring outdoors by mosquitoes that escape insecticides or other indoor control methods [9][10][11][12]. Mosquito entry rate and consequent disease transmission are affected by house type [13], and it is widely acknowledged that poor quality housing -constructions with wooden roofs, straw, clay bricks and roof plates, or clay roofs, for example -is generally believed to be an important contributor to ill health [14].…”

“…Mosquito entry rate and consequent disease transmission are affected by house type [13], and it is widely acknowledged that poor quality housing -constructions with wooden roofs, straw, clay bricks and roof plates, or clay roofs, for example -is generally believed to be an important contributor to ill health [14]. Recently, new approaches based on the design of house ceilings, doors, windows and eaves were developed to block and reduce mosquitoes entering into houses and thus transmitting disease [12][13][14]. Furthermore, approaches that exploit insect behaviour with regards to house entry have been explored as part of malaria vector control strategies [17,18].…”