Anopheles species composition
A total 12 person-nights and 6 person-mornings were used to collect mosquitoes each month, representing a total of 144 person-nights and 72 person-mornings in the night and the morning, respectively, during the entire investigation. This resulted, from January to December 2015, in the collection of 680 female Anopheles according the following distribution: 588 (86.49%) specimens in the night and 92 (13.50%) in the day. Morphological identification enabled us to highlight the presence of Anopheles ziemanni, Anopheles pharoenis and species which belong to the An. gambiae complex and An. funestus group. In order to have the precise species composition of the Anopheles population, molecular identification was carried out on specimen of An. gambiae complex and An. funestus group. During the night, An. arabiensis and An. funestus represented 261 (44.38%) and 247 (42%) of the collection, respectively. At the same time, Anopheles coluzzii and An. gambiae sensu stricto (s.s.), both of which belong to the An. gambiae complex, were found in the proportions of 26 (4.42%) and 20 (3.40%), respectively. However, PCR did not allow us to identify nine (1.53%) specimens of An. gambiae sensu lato (s.l.) caught during the night. Anopheles ziemani and An. pharaonis represented 16 (2.72%) and nine (1.53%), respectively, of the entire night-time collection. In the daylight collection, 53 An. funestus (57.60%), 37 An. arabiensis (40.21%) and two An. coluzzii (2.17%) were collected.
Anopheles biting pattern
Overall, from 7pm to 11am, the biting rate was at 2.56 bites/person. The HBR was significantly different during the night and the day with 3.84 bites per night (bpn) and 1.27 bites per morning (bpm) (Incidence rate ratio (IRR) =3.04, 95% confidence intervals [CI] = [1.84-5.00], p<0.001), respectively. Anopheles arabiensis and An. funestus were the main species biting humans both at night and day. During the night, An. arabiensis and An. funestus had almost the same biting rate, 1.81 bpn and 1.71 bpn, respectively (Fig. 1) (IRR=0.95, CI= [0.46-1.92], p=0.88). During the day, the biting rate of An. funestus (0.73 bpm) was slightly higher than that of An. arabiensis (0.51 bpm) (IRR=1.47, CI= [0.58-3.71], p=0.41) (Fig. 1). However, during the whole study period and both during the day and the night, there was no significant difference between the biting rate of An. arabiensis and An. funestus (IRR=1.06 [0.61-1.82]; p=0.83). At the same time, the biting rate the biting rate of An. arabiensis was significantly higher than that of An. coluzzii (IRR=0.09, CI= [0.03-0.24]; p<0.001) and An. gambiae s.s. (IRR=0.06, CI= [0.02-0.19]; p<0.001). The An. coluzzii biting rates was 0.18 bpn and 0.02 bpm, whereas An. gambiae s.s. biting activity was noticed only during the night (0.13 bpn) (Fig. 1).
Anopheles hourly activity
Anopheles funestus and An. arabiensis aggressiveness increased progressively throughout the first half of the night (7pm-12 midnight) reaching 0.20 and 0.17 bites per hour, respectively. During the second part of the night (12 midnight-7am), two peaks were observed for both vectors (Fig. 2). The first peak was recorded between 1am and 2am with an HBR of 0.29 and 0.31 bites per hour for An. funestus and An. arabiensis, respectively. The second peak was observed at the end of the second part of the night, between 4am-5am for An. funestus (0.24 bph) and between 5am-6am for An. arabiensis (0.17 bph). The HBR of An. coluzzii and An. gambiae s.s. was very low and constant, despite weak peaks of activity occurring between 11pm-12 midnight, between 6am-7am for An. coluzzii, and between 1am-2am for An. gambiae s.s. The peak of activity in morning was observed between 7am and 8am with an HBR of 0.17 bites per hour and 0.09 bite per hour for An. funestus s.s. and An. arabiensis, respectively (Fig. 2) However, when all four species are considered, the hourly activity was not different between the first and de second part of the night (IRR=2.50; CI= [0.21-29.59]; p= 0.46), and between the first part of the night and the morning (IRR=0.94; CI= [0.03-25.53]; p=0.97). Overall, no significant difference was observed between the night and the morning (IRR=0.50; CI= [0.03-7.46]; p= 0.62) (Fig. 2).
Anopheles indoor and outdoor biting activity
The influence of the season (dry season, from December to June with 0.5 mm of cumulative rainfall; rainy season from July to November with 813.38 mm of cumulative rainfall) on Anopheles biting patterns was also evaluated by taking into account the place of biting (indoor/outdoor), the species and period (night/day). Overall during the study, in the night, the HBR was higher during the rainy season (2.520 bpn) compared to the dry season (1.32 bpn) (IRR=2.66; CI= [1.47-4.80]; p=0.001). An. arabiensis outdoor biting rate (2.19 bpn) was higher than that recorded indoor (1.43 bpn) despite the fact that this trend of exophagic behaviour was not significant (IRR=1.53; CI= [0.56-4.19]; p=0.40). An. funestus had a HBR of 0.95 bpn and 2.47 bpn indoors and outdoors, respectively (IRR=2.57; CI= [0.90-7.37)]; p=0.08). The An. coluzzii biting rate was identical indoors and outdoors (0.18 bpn); An. gambiae s.s. showed nearly the same biting rates indoors (0.11 bpn) and outdoors (0.16 bpn) (Fig. 3a). When the season and the biting place are combined, An. funestus did not displayed any significant exophagic behaviour neither in the dry season (IRR=3.12; CI= [0.68-14.28)], p=0.14), nor in the rainy season (IRR=2.27, CI= [0.50-10.32)], p=0.28). The same trend was observed with An. arabiensis in the rainy (IRR=1.5, CI= [0.35-6.29], p=0.57) and dry season (IRR=1.62; CI= [0.34-7.58]; p=0.54) (Table 1).
During the morning, there was no significant difference (IRR=0.91; CI= [0.39-2.10]; p=0.84) between aggressiveness during the rainy (0.51 bpm) and the dry season (0.76 bpm). The An. arabiensis indoor and outdoor HBR was at 0.75 bpm and 0.25 bpm, respectively (IRR= 0.33; CI= [0.072-1.54]; p=0.16) (Fig. 3b) and no significant difference was found (IRR= 0.51; CI= [0.14-1.82]; p=0.30) between the indoors (0.97 bpm) and the outdoors (0.5 bpm) regarding the aggressiveness of An. funestus (Fig. 3b).
During morning, in the dry season, An. arabiensis biting activity was only observed indoors (0.36 bpm) area while in the rainy season it was 0.38 bpd and 0.25 bpm indoors and outdoors, respectively (IRR= 0.64; CI=[0.09-4.33]; p=0.65) (Table 2). In the dry season, the indoor and outdoor aggressiveness of An. funestus was 0.83 bpm and 0.27 bpm (IRR=0.33; CI= [0.06-1.68]; p=0.18), respectively. In the rainy season, its aggressiveness was at 0.13 bpm and 0.22 bpm indoors and outdoors, respectively (IRR= 1.6; CI= [0.16-15.93]; p=0.68) (Table 2). An. coluzzii aggressiveness was only observed indoors and only during the dry season (0.055 bpm) (Table 2).
Anopheles EIR
Throughout the whole study, only two specimens were found to be using to the ELISA-CSP test: one An. arabiensis and one An. funestus collected during the night and the day, respectively. Both positive specimens were caught outdoors, during the dry season. The EIR was, therefore, estimated to be 2.51 infectious bites per person per year during the night compared to 5.03 infectious bites per person per year during the day.