Influence of climatic factors on aggression and infectivity of Anopheles in the districts the Indoor Residual Spray (IRS) in Northern Benin, West Africa.

Background: Climate variability influence the diversity and abundance of malaria vectors and thereby on malaria transmission dynamics. Examine its effect on Anopheles parameters involved in transmission may predict the potential malaria hotspot as a right target for its control intervention strategies. Here, we investigated the influence of meteorological parameters on the aggressiveness and infectivity of Anopheles in two health districts zones where IRS has been extended in Northern Benin. Methods: Mosquito collections were carried out using human landing catches to evaluate rates of aggression and infectivity in twelve villages. Concomitantly, meteorological data from synoptic stations of Benin and neighbouring countries were collected in 2016-2017. Results: The spatial distribution of infective bites of An. gambiae is characterized by an intense aggression in the rural villages of the study area. Analysis of variances showed significant HBR difference according to the period but not according to the locality. However, the same analysis carried out with the infectivity rate shows no significant difference according to the period and the locality. In addition, the number of infective bites per man per month is higher in August and October, and the climatic parameters that have mainly favoured aggression are wind speed, humidity, sunshine and temperature. Indeed, the peak of wind speed is concentrated around 1.2 km / h and in September (5 km / h) whereas the aggressiveness score of Anopheles in the region is greater than 10 infective bites per man a year. Conclusion Malaria transmission by Anopheles is influenced by climatic factors. The climate observed in the districts where IRS was extended in northern Benin has a real impact on Anopheles density and weakens current and future vector control strategies. This could lead to a series of modifications observed in anopheline populations just after IRS implementation ranging from a tendency to exophagy, from a decrease in the rate of blood-feeding to changes in the time, and change in aggressiveness. These phenomena most likely contribute to the sustainability of malaria transmission despite vector control measures.


Introduction
Malaria is a climate sensitive disease and climatic data can be used to monitor and predict aspects of its spatial distribution [1,2]: seasonality [3], year-to-year variability [4], and long term trends [5].
Moreover, climatic information's are increasingly used in the assessment of the real impact of malaria interventions [6,7].
However, environment is a major determinant of malaria biodiversity and its transmission nature is highly depending on vector density, bioecology and blood feeding preferences [11] The survival of major malaria vectors and their adaptation to extreme weather conditions in the form of long and dreadful drought in some places of Africa, especially in semi-desert areas, remains not well elucidated [12,13]. In these areas, the water required for the development of Anopheles larvae is non-existent throughout the year (6-8 months) [14,15] and the replenishment of larvae observed from the start of the rainy season in larval habitats of Anopheles remains poorly documented [16]. It should be noted that the climatic factors were also favorable for larvae and adult mosquitos' development [17]. Fully sunny and quite warm temples were rather favorable to the aggressiveness and infectivity of mosquitoes from temporary submerging wetlands [18]. The observations made in the field are formal: the number and aggressiveness of mosquitoes increase in areas of very short duration and high malaria transmission (www.lerepublicain.net). In the northern part of Benin where the dry season lasts about a semester, many cases malaria are diagnosed during the dry season at consultations in health facilities [19]. Although these unexpected cases were related to relapses or cases of imported malaria case, the possibility of recent infections is not to be discounted given the magnitude of the incidence.
The aim of this study is to investigate the impact of different climatic parameters on the temporal dynamics of aggressiveness and infectivity among Anopheles in northern Benin. This research will enable the Ministries of Health and Environment to better refine their strategies in order to protect populations from mosquito bites.

Study sites
The study was carried out in two health zones composed of six districts in northen Benin: Kandi-Gogounou-Ségbana health zone in Alibori province and Djougou-Copargo-Ouaké health zone in Donga province (Fig. 1). These sectors are selected by the National Malaria Control Program (NMCP) based on epidemiological, ecological, environmental and socio-economic criteria to extend IRS operations from 2017. The region's crop diversity includes yams, sorghum, maize, millet, cowpeas, cassava, beans and groundnuts for food-producing crops and cotton, shea and cashew for cash crops.
Collecting and processing cashew and shea are the main sources of income for the populations.
Kandi-Gogounou-Ségbana health districts zone is about 12,943 km 2 , the cumulative incidence of malaria cases is 14.1% across all ages and the mortality due to malaria is 6.2% for children aged 0-4 years in 2015 [20] (MS, 2016). Djougou-Copargo-Ouaké health district zone is about 5,465 km 2 with 397,942 inhabitants in 2012, the cumulative incidence of malaria cases is 28% and the mortality due to malaria is XXX in 2015 [21]. Long-lasting insecticidal nets (LLINs) are the main tool for malaria prevention in these districts.

Study of population dynamics of vectors and malaria transmission
From May 2016 to February 2017, a longitudinal study was conducted to assess the spatio-temporal dynamics of Anopheles mosquitoes and malaria transmission in the northern part of Benin Republic.
For this study, Anopheles mosquito collections were conducted in twelve (12)

Human landing catches
This method contributed to the evaluation of the interactions between the vector and the human host.
As the number of vectors which bite humans per unit of time is an important parameter in estimating the level of malaria transmission, it revealed which Anopheles bite humans, which species are vectors of malaria, how many times a person is bitten by a vector per unit of time, and whether the vectors bite inside or outside the dwellings. As part of this study, HLC were carried out from May 2016 to Mosquito screening for Plasmodium falciparum sporozoite for Sporozoitic Index (SI) estimation The head and thorax of each mosquito was carefully separated from the abdomen and tested for the presence of P.falciparum circumsporozoite protein (CS) as described by [22]. Briefly, mosquitoes were In order to have the climatic data in all points of the two health zones, spatial interpolations of the temperature, the rainfall, the wind speed, the vapor pressure, etc were carried out. Through these interpolations, zonal statistics were recorded for each of the twelve study localities. The extension '' plot is a maneuver '' for successful batch sharing of different climatic and entomological variables in geographical and temporal settings. It is used to explore the relationship between three variables on a block to subdivide, consider the combinations of X and Y that produce the corresponding values for the predictors on the X and Y axes while the outlines of lines and color bands of values for the Zfactor (involvement or reaction). Some analyzes including correlation, regression, Student Newman Keulset, and Principal Component Multivariate Analysis (PCA) were carried out with Minitab 15 and SAS software.

Results
Spatial distribution of Anopheles aggressiveness in the study area The spatial distribution of infective bites of An. gambiae s.l. (Fig. 2) is characterized by an intense aggressiveness in the rural villages (Sonsoro, Gounarou, Liboussou, Barienou, Kataban, Aboulaoudè) of the study area. Such a distribution makes it possible to suspect that, after being fully blood-fed, a multitude of female Anopheles leave in search of rest sites to digest their meal. Two days later, these vectors easily find the natural reservoirs of stagnant water not heavily polluted (preferably sunny and with vegetation) and of different sizes such as ponds, swamps, puddles and leaves that are potential areas for egg-laying and larval breeding.

Variation of infected mosquitoes according to degree of urbanization and season
A total of 3788 mosquitoes were tested in the laboratory and 305 mosquitoes (8.05%) are infected with 50 identified during the dry season (May 2016-January, February 2017) and 255 during the rainy season (June, July, August and October 2017). However, depending on the degree of urbanization, 82% of the malaria vector mosquitoes were in the rural areas and18% in the urban areas ( Table 1).
Variation of human biting and infectivity rates according to localities and periods Table 2 shows the results of variance analyses carried out on localities and the period according to the different numbers of infective bites per man and per month (HBR) as well as the infectivity rate (IS). It appears from this table that there was significant difference of HBR (p> 0.001) according to the period but no significant difference was observed per location. Similarly, the analysis of variances of the infectivity rates does not show any significant difference according to the period and the locality. These analyses show that HBR varies from one month to another. The mean sporozoite rates for An. gambiae s.l. over the the study period are estimated at 4.54%.
Student Newman Keuls (SNK) tests showed higher monthly HBR in July and August whereas lower rate was recorded in May, June, January and February. The correlation and regression analyzes identified climatic factors which led to the increase in HBR during August and October ( Table 3)

Factors involved in the aggressiveness of anopheles in the commune of Djougou
The hierarchical ascending classification (HAC) analysis based on 5 parameters which determine the occurrence of transmission more clearly allows distinguishing four categories of factors with a clear separation between sets (Fig. 13). The classification represented by the dendrograms shows four categories of aggressiveness parameters. The first includes the ETP and the sunshine. The second includes temperatures, representing the class of parameters which are favorable to the aggressiveness of Anopheles in the district. The third is the category of humidity, which actually is the class of amplifier parameters and it determines the number of bites received by a person in the area.

Finally, the fourth which includes rains is the class of factors for recovery of mosquito bites. Discussion
The study of the influence of climatic parameters on the aggressiveness and infectivity of Anopheles s.l in North Benin is essential not only to understand the effect of climate on the dynamics of transmission but also to establish a effective and targeted control of these vectors taking into account climate variability. The study was carried out in two health zones composed of six communes of Climatic parameters which have mainly favored aggression are wind speed, humidity, sunshine and temperature. These works are similar of mosquitosquad [29] in 2018 which those the recipe for mosquito activity is heat + rainfall = humidity, and this, combined with stagnant water means the perfect soupy combination for mosquito madness The temperature and activity of mosquitoes go hand in hand with insects that thrive in humid and relatively warm environments, working best at 20°C (80°F). Once the temperature has decreased to about 20°C (60°F), they become lethargic and, below 50°C (80°F), it is difficult to operate. If it's too hot and too dry, mosquitoes will not be as active and will not feed as usual. But once the temperature drops a little and is within the tolerable range for mosquitoes, they get more hungry and therefore bite more. Cameroon where these authors showed that the anophelian density is seasonal. Each peak or decrease in rainfall was responsible for an increase or decrease in the population of An. gambiae s.l.
Student Newman Keuls (SNK) tests showed higher monthly HBR in July and August whereas lower rate was recorded in May, June, January and February. De plus, the correlation and regression analyzes identified climatic factors which led to the increase in HBR during August and October. This duration of strong anopheles aggressiveness is lower than those obtained in the municipality of Corpargo in northeastern Benin (Yadouléton et al.,, 2018) [30]. However, the months of May, July and September are the months when populations receive more bites. In addition, research on P. falciparum infectivity shows that no infected individuals were found in the population of An. Funestus. This would probably be due to the small number of mosquitoes tested.
This study shows that the lack of access to controlled meteorological and entomological data acrossall months of the year and their quality has considerably undermined the quality of the climate and the analysis of some control indicators.
Whether or not observed increases in infectivity and aggressiveness in northern Benin during the last thirty years are associated with co-varying changes in local temperature, possibly connected to global changes in climate, has been debated for decade. Studies, using differing data sets and methodologies, produced conflicting results regarding the occurrence of temperature trends and their likelihood of being responsible, at least in part, for the increases in malaria transmission in Northern Sudan.
A time series of quality controlled daily temperature and rainfall data from northern Benin.
In order to develop a pre-alert system for Benin, not only is it essential to monitor the vulnerability of the population to increased malaria transmission, but it is also important to predict and observe weather conditions. It appears that replacement of natural swamp vegetation with agricultural crops has led to increased climatic parameters, which may be responsible for elevated malaria transmission risk in cultivated areas.

Conclusions
The objective of this study is to study the influence of climatic parameters on the aggression and infectivity of Anopheles sl in the implementation communes of the strategy of large-scale indoor spraying to fight against malaria in the North. East of Benin. This study showed that climatic factors contributed more to the strong anopheles activity from June to August in the study area. The climate observed in northern Benin has a real impact on Anopheles density and weakens current and future vector control strategies.
The present results provide information on the temporal and geographical influence of the entomological and climatic parameters favorable to the transmission of malaria and will be of great utility for the decision-making regarding the quality of the effectiveness of vector control against malaria. Malaria in North Benin.

Competing interests
The authors declare having no competing interests.

Acknowledgment
It is my pleasure to extend my sincere gratitude and appreciation to the collaborators of the Center of Entomological Research of Cotonou, in particular USAID, WHO, and Benin NMCP for their interest in my work and for the development of scientific research in Africa. We are very grateful to the people in our study area who kindly allowed us to have access to their houses to sample mosquitoes, as well as to the numerous volunteers who daily recorded temperature. Eventually, we would like to express our sincere gratitude to Dr.Azondekon Roseric for providing us with linguistic support and other corrections.

Funding
This study was financially supported by the US President's Malaria Initiative (PMI) through the United States Agency for International Development (USAID) Africa Indoor Residual Spraying Project (AIRS).

Availability of data and materials
The data supporting the conclusions of this article are included within the article. The raw data used and/or analyzed in this study are available from the corresponding author upon reasonable request.

Ethical consideration
Permission was sought from households to perform collections in their rooms. In addition, community consent had been obtained beforehand in all the villages. The volunteer mosquito collectors gave their consent before participating in the study. They were also subjected to regular medical check-ups with preventive malaria treatment. They were all vaccinated against yellow fever. This study received the approval of the Ethical Institutional Committee of the Centre for Entomological Research of Cotonou (CREC), Ministry of Health.
.Consent for publicationNot applicable.Competing interestsThe authors declare having no competing interest.   Multivariate map of the influence of the wind speed in HBR-months to Copargo Figure 5 Multivariate map of the influence of wind in HBR-month function at Kandi Figure 6 Multivariate map of the influence of wind in HBR-month function at Gogounou Figure 7 Multivariate map of the influence of sunshine on HBR-month function at Kandi Figure 8 Multivariate map of the influence of sunshine on HBR-month function in Gogounou Figure 9 Multivariate map of the influence of sunshine on HBR-month in Djougou Figure 10 Graph showing PCA results on HBR according to climatic parameters in Copargo Figure 11 Graph showing PCA results on HBR according to climatic parameters in Gogounou Figure 12 Graph showing PCA results on HBR as a function of climatic parameters in Kandi.

Figure 13
Difference diagram of the 4 groups of the hierarchical ascending classification (HAC)

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