Anopheles species composition
From January to December 2015, a total of 680 female anopheles were collected 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 An. ziemani, An. pharaonsis and species which belong to the An. gambiae.s.l complex and An. funestus group. In order to have the precise species composition of the anopheles population, molecular identification was carried out on An. gambiae s.l. complex and An. funestus group specimens. During the night, An. arabiensis and An. funestus represented 261 (44.38%) and 247 (42%) of the collection, respectively. At the same time An. coluzzii and An. gambiae s.s species, wich belong to the An. gambiae s.l. 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 s.l caught during the night. An. ziemani and An. pharaonsis 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 day (bpd) (p<0.001), respectively. An. 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 (figure 1) (p=0.80). During the day, the biting rate of An. funestus (0.73 bpd) was slightly higher than that of An. arabiensis (0.51 bpd) (Figure 1) (p=0.30). 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 (p=0.84), and the aggressiveness of An. coluzzii and An. gambiae s.s. was significantly lower than that of An. arabiensis and An. funestus (p<0.001). The An. coluzzii biting rates was 0.18 bpn and 0.02 bpd, whereas An. gambiae s.s. biting activity was noticed only during the night (0.13 bpn) (Figure 1).
Anopheles hourly aggressiveness
An. 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 of aggressiveness were observed for both vectors (Figure 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 aggressiveness occurring between 11pm-12 midnight, between 6am-7am for An. coluzzii, and between 1am-2am for An. gambiae s.s. However, there was no significant difference in the level of aggressiveness between the first and the second part of the night (p= 0.45) (Figure 2). The peak of aggressiveness in daylight 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 (Figure 2).
Anopheles indoor and outdoor biting activity
The influence of the season (dry season: 0.5 mm of rainfall; rainy season: 813.38 mm of 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) (p<0.001). Regardless of the season, the outdoor biting rate (5.01 bpn) was significantly higher than indoor aggressiveness (2.68 bpn) (p= 0.004). Depending on the place of the biting, the 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 (p>0.168) An. funestus had a HBR of 0.95 bpn and 2.47 bpn indoors and outdoors, respectively (p=0.006). 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) (figure 3a).When the season and the biting place are combined, only An. funestus displayed significant exophagic behaviour both in the rainy and dry seasons. An. funestus HBR was at 1.08 bpn and 0.34 bpn outdoors and indoors, respectively in the dry season (p <0.043) (Table 1a). In the rainy season, outdoor and indoor aggressiveness was at 1.38 bpn and 0.61 bpn, respectively (p=0.06) (Table 1a). The vectors belonging to the An. gambiae s.l. complex did not show any significant difference. During the rainy season, the aggressiveness of An. arabiensis was 1.02 and 1.54 bpn indoors and outdoors, respectively (p=0.27) while it was 0.40 bpn indoors and 0.65 bpn outdoors (p=0.40) in the dry season (Table 1a). The An. coluzzii feeding rate was at 0.13 bpn and 0.06 bpn outdoors and indoors, respectively during the rainy season (p=0.61), while the opposite trend was observed in the dry season (0.11 bpn indoors and 0.04 bpn outdoors) (p=0.55) (Table 1). In the rainy season, An. gambiae s.s. displayed a biting rate of 0.09 bpn and 0.16 bpn indoors and outdoors, respectively (p=0.64). In the dry season, aggressiveness was only observed indoors (0.01 bpn) (Table 1a).
During the daytime there was no significant difference (p=0.81) between aggressiveness during the rainy (0.51 bpd) and the dry season (0.76 bpd) and the indoor aggressiveness (1.77 b/p/d) was significantly higher than that recorded outdoor (0.75 bpd) (p=0.03). The An. arabiensis indoor and outdoor HBR was at 0.75 bpd and 0.25 bpd, respectively (p=0.099) (Figure 3b) and no significant difference was found (p=0.186) between the indoors (0.97 bpd) and the outdoors (0.5 bpd) regarding the aggressiveness of An. funestus (Figure 3b). During daylight during the dry season, An. arabiensis biting activity was only observed indoors (0.36 bpd) area while in the rainy season it was 0.38 bpd and 0.25 bpd indoors and outdoors, respectively (p=0.55) (Table 1b). In the dry season, the indoor and outdoor aggressiveness of An. funestus was 0.83 bpd and 0.27 bpd (p=0.082), respectively. In the rainy season, its aggressiveness was at 0.13 bpd and 0.22 bpd indoors and outdoors, respectively (p=0.634) (Table 1b). An. coluzzii aggressiveness was only observed indoors and only during the dry season (0.055 bpd) (Table 1b).
Throughout the study, two anopheles specimens were found to be positive using the ELISA-CSP test and were collected during the night and the day. 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 infected bites per person per year during the night compared to 5.03 infected bites per person per year during the day.