Residual malaria transmission in central-western Senegal: role and bionomics of the local populations of Anopheles arabiensis and Anopheles melas

doi:10.21203/rs.3.rs-2090428/v1

Background

Understanding the behavior and ecology of local malaria vectors is essential for the effectiveness of the commonly used vector-targeted malaria control tools in areas of low malaria transmission. This study was conducted to determine species composition, biting behavior and infectivity of the major Anophelesvectors of Plasmodium falciparum in low transmission settings in central western Senegal.

Methods

Adult mosquitoes were collected using human landing catches (HLCs) during two consecutive nights and Pyrethrum Spray Catches (PSCs) in 30 to 40 randomly selected rooms, from July 2017 to December 2018 in three villages. Anopheline mosquitoes were morphologically identified using conventional keys; their reproductive status assessed by ovary dissections, and a sub-sample of An. gambiae s.l. were identified to species level using polymerase chain reaction (PCR). Plasmodium sporozoite infections were detected using real-time quantitative PCR (qPCR).

Results

During this study 3684 Anopheles were collected of which 97% were An. gambiae s.l., 0.6% were Anopheles funestus and 2.4% were Anopheles pharoensis. Molecular identification of 1877 An. gambiae s.l. revealed a predominance of An. arabiensis (68.7%), followed by An. melas (28.8%) and An. coluzzii (2.1%). The overall human biting rate of An. gambiae s.l. was highest in the inland site of Keur Martin with 4.92 bites per person per night, while it was similar in the deltaic site, Diofior (0.51) and the coastal site, Mbine Coly (0.67). Parity rates were similar in An. arabiensis (45%) and An. melas (42%). Sporozoite infections were detected in both An. arabiensis and An. melas with the respective infection rates of 1.39% (N=8) and 0.41% (N=1).

Conclusion

Results suggest that low residual malaria in central western Senegal is transmitted by An. arabiensis and An. melas. Consequently, both vectors will need to be targeted as part of malaria elimination efforts in this area of Senegal.

Hotspots

Malaria Elimination

An. arabiensis

An. melas

q-PCR

central-western Senegal

Malaria remains one of the most important parasitic diseases worldwide. According to WHO, 241 million malaria cases and 627,000 deaths were reported worldwide in 2020, representing increases of 6% and 12%, respectively, compared to 2019 [1]. Service disruptions during the COVID-19 pandemic are likely to have contributed to these increases, but a stagnation in malaria declines was also observed in many parts of Sub-Saharan Africa prior to the pandemic [1]. In contrast, between 2015 and 2019, Senegal recorded a 38% decrease in the number of malaria cases (from 69 to 50 per 1,000 population) and a 7% decrease in malaria deaths (from 0.30 to 0.28 per 1,000 population) [2] and is among the countries displaying the lowest malaria incidence in the Western African region.

Malaria transmission is typically more intense where the anopheline species have marked preference for humans and live long enough to allow completion of parasite sporogony development. The lifespan of African anopheline species and their highly anthropophilic behavior are among the reasons that the continent bears the highest malaria burden worldwide [3]. Across Sub-Saharan Africa, the primary malaria vectors belong to the Anopheles gambiae sensu lato (s.l.) complex and An. funestus s.l. group, targeting of which by vector control interventions is considered crucial for malaria control and elimination. In Senegal, 22 anopheline species have been reported [4-6], of which four are Anopheles gambiae s.l. (An. arabiensis, An. melas, An. gambiae and An. coluzzi), which along with An. funestus s.s. are reported as the primary malaria vectors [7,8,9,10,5,11,12].

In the central-western part of Senegal, the implementation of several control interventions, including seasonal malaria chemoprevention (SMC) from 2008 to 2011 followed by community-based indoor residual spraying (IRS) with pirimiphos-methyl between 2013 and 2014, and universal LLIN distributions, have contributed to substantially reduce malaria burden in the area [13-15]. However, despite the success recorded at the regional administrative level, a few residual transmission hotspot areas persist where especially suitable micro-environmental conditions for vector development occur [16]. Recent investigations in central-western Senegal reported the presence of An. arabiensis, An. coluzzii and An. melas in the hotspots surveyed [12], with local populations displaying resistance to several public health insecticides [17].

This longitudinal entomological study took place between July 2017 and December 2018 in three mains ecological (coastal, deltaic, and inland) settings in central-western Senegal to clarify the potential role and relative contributions of local populations of An. arabiensis and An. melas in maintaining malaria transmission in local hotspots.

Study area

This study was conducted in three sites located, respectively, in the coastal, deltaic, and inland (continental) areas in the centre-west of Senegal spanning the administrative departments of Mbour and Fatick. The village of Mbind Coly (14° 17' 10'' N; 16° 54' 30'' W) is located in the coastal estuary of Mbour department and is surrounded by a mangrove swamp fed by rainwater and tides. The village of Diofior (13° 58’ 41’’N; 16° 45’ 45’’ W) is located in the deltaic area where the Saloum River flows into the Atlantic Ocean. The village of Keur Martin (14° 24’ 29’’N; 16° 34’ 29’’ W) is located in the western mainland in the department of Fatick and is characterized by the presence of saline soils (Fig. 1). Detailed description of the three study sites and areas are reported in Ndiaye et al. (2020) [16] and in Sy et al. (2018; 2021) [17].

Mosquito sampling and processing

The dynamics of malaria vector populations were monitored in each of the study villages using overnight human landing catches (HLC) and Pyrethrum Spray Catches (PSC) in the morning. HLC were performed between 8 pm and 6 am for two consecutive nights in three randomly selected houses, where two collectors catch landing host-seeking, one indoor and another outdoor distant at least 10 meters apart from each another. PSC were performed early in the morning, after the second overnight HLC, at least 30 up to 40 randomly selected rooms per village with one room per house. Collections were carried out in July, September, October, and December 2017; then in April, May, July, August, September, October and December 2018. The use of long-lasting insecticide-treated nets (LLINs) by people in the PSC selected rooms was also reported in a survey form to determine LLINs coverage among the sampled rooms.

Field and Laboratory Processing

Collected mosquitoes were morphologically identified to genus level, and Anopheles were subsequently identified to species level using morphological keys [18]. All mosquito specimens were stored individually in numbered vials with desiccant until laboratory processing. For each collection, 30 randomly-sampled female specimens of Anopheles gambiae s.l. caught using HLC were dissected to determine the parity rate. The heads and thoraxes of host-seeking females were screened to detect Plasmodium falciparum infection using the qPCR TaqMan Assay Method described by Bass et al. (2008) [19]. Anopheles gambiae s.l. sibling species were discriminated by the PCR method described by Wilkins et al. (2006) [20].

Measured parameters

The human-biting rate (HBR) was calculated as the ratio of the total number of females of each vector species collected by HLC to the total person-nights for a given collection period. The parity rate was estimated as the proportion parous from the total number of specimens dissected. The indoor resting density was defined as the number of mosquitoes per room collected by PSC. The sporozoite rate was calculated as the proportion of the total number of mosquitoes infected with P. falciparum. The entomological inoculation rate (EIR) was calculated as the product of the human-biting rate (HBR) and the sporozoite rate. LLIN coverage was calculated as the ratio of the number of rooms with nets used to the number of rooms visited during the PSC collection.

Statistical analysis

All parameters measured were computed and analyzed using the RStudio and SPSS® 26 Statistics software. Data were compared with the Pearson chi-square or Fisher exact tests, Spearman correlation, Kruskal-Wallis test, Friedman ANOVA (non-parametric) or a binomial generalized linear model as applicable, with the statistical significance threshold in all cases set at P value ≤ 0.05.

Mosquito densities and species composition

Overall, 3684 anopheline specimens were collected during the study period, of which 97% (3575) were Anopheles gambiae s.l., 0.6% (22) were Anopheles funestus and 2.4% (87) were Anopheles pharoensis. The molecular identification of a sub-sample of 1877 specimens of An. gambiae s.l., including 829 and 1048 randomly selected specimens respectively from HLC and PSC, revealed the predominance in the study area of An. arabiensis with 68.7% (1290) and An. melas with 28.8% (541) followed by An. coluzzii with 2.13% (40). Overall, the species composition was significantly different among the three study sites (Pearson's Chi-squared test, X-squared = 30.4, p-value = 0.0002). However, the proportions of the two most common species were comparable among sites (Pearson's Chi-squared test, X-squared = 0.06, p-value = 0.97). During the study period An. gambiae (0.27%, 5/1877) and coluzzii-gambiae hybrids (0.05%, 1/1877) were the less common members of the complex encountered in the study sites (Table 1).

Table 1

Distribution of *Anopheles gambiae* sibling species by villages
Espèces	Diofior (Delta)
	N	%	N	%	N	%	N	%
An. gambiae	0	0	1	0.08	4	1	5	0.27
An. arabiensis	102	68	920	69.43	268	66.67	1290	68.73
An. coluzzii	5	3.33	20	1.51	15	3.73	40	2.13
An. melas	42	28	384	28.98	115	28.60	541	28.82
Hybrid coluzzii-gambiae	1	0.67	0	0	0	0	1	0.05
Total général	150	100	1325	100	402	100	1877	100

Resting and biting behaviors of Anopheles gambiae s.l. populations

Overall, the resting densities (from PSC) of An. gambiae s.l. were at least two times higher in the inland area of Keur Martin than in both the deltaic area of Diofior and the coastal area of Mbine Coly. Indoor Resting Density (IRD) of An. gambiae s.l. was significantly lower in Diofior than in Mobine Coly and Keur Martin (Friedman chisq = 11.29, P = 0.004). IRD varied seasonally and was the highest between September and October, which coincided with the end of the rainy season in all study sites over the two year the study was conducted. Thus, in Keur Martin a peak of 5.6 and 7.87 females/room were recorded in September 2017 and September 2018, respectively. In Diofior and Mbine Coly the peaks of IRD were observed between September and October in both years (Table 2). The endophagic rates of An. gambiae s.l. females were comparable in all the studied sites with 49% in both Diofior and Keur Martin and 45% in Mbine Coly.

Table 2

Seasonal variation of Indoor Resting Density (IRD) of *Anopheles gambiae* s.l. population
Month-year	Diofior (Delta)		Keur Martin (inland )		Mbine Coly (Costal)
Month-year	Collected	IRD	Collected	IRD	Collected	IRD
Jul-17	0	0.00	32	1.07	22	0.73
Sept-17	3	0.10	168	5.60	83	2.77
Oct-17	6	0.20	46	1.53	55	1.83
Nov-17	0	0.00	0	0.00	0	0.00
Dec-2017	3	0.10	8	0.27	11	0.37
Feb-2018	0	0.00	0	0.00	0	0.00
Apr-2018	0	0.00	0	0.00	0	0.00
Jul-18	9	0.23	16	0.53	28	0.93
Aug-Sept 2018	5	0.13	236	7.87	19	0.63
Oct-18	29	0.73	102	3.40	93	3.10
Dec-2018	4	0.10	67	2.23	3	0.10
Total	59	0.24	675	2.05	314	0.95
IRD = Indoor Resting Density

The human biting rate of An. gambiae s.l. was the highest in September and October during each year of study. During these two months (September & October) no significant difference was noted in HBR among sites, with 4.92 bites per person per night (b/p/n)) in the mainland area of Keur Martin, 0.51 b/p/n in Diofior and 0.67 b/p/n in Mbine coly (Friedman chisq = 3.93; P = 0.14). Similarly, no significant difference was found in indoor biting proportion (Friedman chisq = 0.80; P = 0.67) (Table 3).

Table 3

Seasonal variation of human biting rates and endophagous rates of *An. gambiae* s.l
Month-year	Diofior (Delta)			Keur Martin (inland)			Mbine Coly (Costal)
Month-year	Caught	HBR	Indoor (%)	Caught	HBR	Indoor (%)	Caught	HBR	Indoor (%)
Juil-17	6	0.50	50	37	3.08	59	10	0.83	30
Sept-17	26	2.17	38	149	12.42	39	37	3.08	49
Oct-17	10	0.83	50	71	5.92	54	17	1.42	59
Nov-Dec 2017	3	0.25	67	7	0.58	43	7	0.58	57
Fev-2018	0	0.00	0	0	0.00	0	0	0.00	0
Apr-2018	2	0.17	100	0	0.00	0	0	0.00	0
Juil-18	5*	0.21	40	4	0.33	0	4	0.33	25
Aug-Sept 2018	3*	0.13	0	382	31.83	50	2	0.17	50
Oct-18	36*	1.50	58	0	0.00	0	11	0.92	27
Dec-2018	0*	0.00	0	0	0.00	0	0	0.00	0
Total	91	0.51	49	650	4.92	49	88	0.67	45
*From July 2018 two villages are monitored in Diofior and 24 men were used for the 4 nights of human landing catches.

Among the study sites, significant difference was observed in LLIN coverage with 70% in Mbine Coly, 91% in Keur Martin and 95% in Diofior (Chi-squared test, X-squared = 6.24, 2 degrees of freedom, P = 0.044) (Table 4).

Table 4

LLINs coverage rate in selected PSC rooms in the different sites.
Locality	Number of visited houseold	Number of LLINs used	LLIN coverage rate
Mbine Coly	315	222	70%
Keur Martin	696	630	91%
Diofior	59	56	95%

Parity rates of An. gambiae s.l. females

The parity rate of An. gambiae s.l. females were 38.9% in the inland area of Keur martin, 56.6% in the coastal zone of Mbine Coly and 59.6% in the deltaic zone of Diofior. Using a generalized linear binomial model initially including collection month, location, species (An. arabiensis or An. melas), and a location x species interaction term, only location was significant in the minimal model. Parity rate was significantly lower in Keur Martin than in the reference location Mbine Coly (P = 0.023), but Diofior was not significantly different (P = 0.30) (Table 5). In all the study sites, An. arabiensis displayed the highest parity rate compared to An. melas except in the coastal site of Mbine coly where the GLM – species model revealed no significant difference in the parity rate between the two species (Chi-squared = 5.54; df = 2, P = 0.063) (Table 6).

Table 5

Seasonal variation of Parity Rate of females of *An gambiae* s.l caught by HLC
Month-year	Diofior (Delta)			Keur Martin (inland)			Mbine Coly (Costal)
Month-year	Dissected	Parous	P (%)	Dissected	Parous	P (%)	Dissected	Parous	P (%)
July-17	3	2	66.6	24	12	50	5	4	80
Sept-17	16	10	62.5	42	14	33.3	22	15	68.1
Oct-17	8	3	37.5	37	10	27	14	6	42.8
Nov-Dec 2017	2	1	50	4	2	50	3	2	66.6
Feb-2018	0	0	0	0	0	0	0	0	0
Apr-2018	0	0	0	0	0	0	0	0	0
July-18	1	0	0	0	0	0	3	3	100
Aug-Sept 2018	2	1	50	100	49	49	2	1	50
Oct-18	19	13	68.4	0	0	0	11	3	27.2
Dec-2018	0	0	0	0	0	0	0	0	0
Total	52	31	59.6	213	83	38.9	60	34	56.6

Table 6

Seasonal variation of Parity Rate of females of *An. arabiensis* and *An. melas*
Month-year	Diofior (Delta)
	An. arabiensis		An. melas		An. arabiensis		An. melas		An. arabiensis		An. melas		An. arabiensis		An. melas
	Dissected	P%	Dissected	P%	Dissected	P%	Dissected	P%	Dissected	P%	Dissected	P%	Dissected	P%	Dissected	P%
July-17	0	0	3	67	18	50	6	50	1	0	4	100	19	47	13	69
Sept-17	8	63	7	57	16	31	26	35	18	67	4	75	42	52	37	43
Oct-17	2	50	6	33	7	0	30	33	8	50	6	33	17	29	42	33
Nov-Dec 2017	0	0	2	50	0	0	4	50	3	67	0	0	3	67	6	50
Feb-2018	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Apr-2018	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
July-18	1	0	0	0	0	0	0	0	0	0	3	100	1	0	3	100
Aug-sept 2018	1	100	1	0	93	45	5	40	1	0	1	100	95	45	7	43
Oct-18	14	79	4	50	0	0	0	0	10	20	1	100	24	54	5	60
Dec-2018	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Total	26	69	23	48	134	42	71	37	41	24	19	74	201	42	113	45

Sporozoite infection and entomological inoculation rates (EIR)

The screening of Plasmodium infection suggests that An. arabiensis and An. melas are involved in the residual malaria transmission, with the respective infection rates of 1.39% (N = 8) and 0.41% (N = 1). No significant difference was observed between species (Fisher exact P = 0.29) nor between study sites with species pooled (Fisher exact P = 0.87). Infected An. arabiensis females were found in Keur Martin (inland area) and Diofior (deltaic area) with the respective infection rates of 1.52% and 1.85%. An. melas was found infected only in the inland area (0.54%) (Table 7). No infection was found in the coastal area for both species.

Table 7

Local and seasonal variation of sporozoite infection rates of females of *An. arabiensis* and *An. melas* caught by HLC.
Month-year	Diofior (Delta)						Keur Martin (inland)						Mbine Coly (Costal)							TOTAL
	An. arabiensis			An. melas			An. arabiensis			An. melas			An. arabiensis				An. melas			An. arabiensis				An. melas
	tested	Positive	CSPR (%)	tested	Positive	CSPR (%)	tested	Positive	CSPR (%)	tested	Positive	CSPR (%)	tested	Positive	CSPR (%)	tested		Positive	CSPR (%)	tested	Positive	CSPR (%)	tested		Positive	CSPR (%)
July-17	0	0	0	6	0	0	26	0	0	11	0	0	1	0	0	9		0	0	27	0	0	26		0	0
Sept-17	15	0	0	10	0	0	60	0	0	89	0	0	32	0	0	4		0	0	107	0	0	103		0	0
Oct-17	4	0	0	6	0	0	11	0	0	59	0	0	10	0	0	7		0	0	25	0	0	72		0	0
Nov-Dec 2017	0	0	0	3	0	0	1	0	0	6	1	16.67	7	0	0	0		0	0	8	0	0	9		1	11.11
Sub total	19	0	0	25	0	0	98	0	0	165	1	0.61	50	0	0	20		0	0	167	0	0	210		1	0.48
Feb-2018	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0		0	0	0	0	0	0		0	0
Apr-2018	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0		0	0	2	0	0	0		0	0
July-18	5	0	0	0	0	0	4	0	0	0	0	0	0	0	0	4		0	0	9	0	0	4		0	0
Aug-sept 2018	1	0	0	1	0	0	358	7	1.96	21	0	0	1	0	0	1		0	0	360	7	1.94	23		0	0
Oct-18	27	1	3.70	7	0	0	0	0	0	0	0	0	10	0	0	1		0	0	37	1	2.70	8		0	0
Dec-2018	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0		0	0	0	0	0	0		0	0
Sub total	35	0	0	8	0	0	362	0	0	21	0	0	11		0	6		0	0	408	0	0	35		0	0
Total	54	1	1.85	33	0	0	460	7	1.52	186	1	0.54	61	0	0	26		0	0	575	8	1.39	245		1	0.41

Overall, in the study area, despite the presence of An. coluzzii and An. gambiae, only An. arabiensis and An. melas seem to play a role in malaria transmission, being the only species found infected with respectively entomological inoculation rates (EIR) of 0.018 ib/p/n and 0.002 ib/p/n, corresponding to an annual infected bites of 6.57 ib/p/year for An. arabiensis and 0.73 ib/p/year for An. melas. Both species were found infected in the same locality at the same time only in the inland area of Keur Martin (Table 7). No Plasmodium infection was found in the coastal area of Mbine Coly, whereas in the deltaic area of Diofior, only An. arabiensis was found infected with an EIR of 0.0055 ib/p/n (or 2 ib/p/year (Fig. 2).

This study was conducted over two consecutive years in 2017 and 2018 and confirmed the predominance of Anopheles gambiae s.l. representing 97% of the anopeline fauna with minor presence of other species, Anopheles funestus and Anophele pharoensis. Indeed, the An. gambiae s.l. complex contains the major malaria vectors among the 22 species described nationwide [4–5]. The use of molecular approaches on morphologically identified An. gambiae s.l. revealed the presence of 4 members of the gambiae complex: An. arabiensis, An. melas, An. gambiae and An. coluzzi, and the presence of gambiae/coluzzii hybrids. In the study area, An. arabiensis and An. melas were the two most abundant species of the gambiae complex. An. arabiensis is known as a predominant malaria vector over all the country specially in the dried and arid environments, except the south and south-east part of Senegal [21, 22, 10]. The presence of An. melas was reported in brackish water resulting from the mixture of sea water with the freshwater of the Saloum River in the deltaic area where it flows into the ocean, known to be provide preferred breeding sites [23, 24]. The indoor resting density of An. gambiae s.l. was relatively important in the inland area of Keur Martin than in the two other areas (deltaic and coastal areas). In contrast to the other study sites, Keur Martin village is characterised by the presence of hydromorphic and halomorphic soils, which in addition to their capacity to retain water over a long period of time, are characterized by the presence of surface brackish water bodies, suitable for the development of An. arabiensis and An. melas depending on the level of salinity [16]. In all the sites, the exophagy rate of An. gambiae s.l females has been relatively important, this situation could be explained by the predominance of An. arabiensis, accounting for 68.72% of the anopheline fauna in the area and known for its behavioral plasticity, being more exophilic in some areas compared to its sibling [25]. Furthermore, the high coverage of LLINs, following the LLIN mass campaign implemented by the PNLP in 2016 across the study area could suggest additional pressure and which could lead to an induced exophilic behavior due to the repellent effect of pyrethroid, the class of insecticide used for net impregnation, as previously shown in an experimental study [26, 27]. The parity rate of An. gambiae s.l. was the lowest in the inland site of Keur martin (38.9%) and was comparable with the rates (25–33%) previously reported from the mangrove area in the Gambia [28] and from Casamance (47%) [24]. The high level of pyrethroid-impregnated LLINs coverage in the studied houses of Keur Martin (> 90%) could explain the reduced longevity of the studied populations of Anopheles gambiae s.l.

Only An. arabiensis and An. melas were found infected in the study area, this finding is in line with recent studies carried out in the central western Senegal [12].

Generally, human populations are at high risk of being infected by malaria local vector species, especially during the second half of the night when they were not effectively using the LLINs. LLINs mass distribution campaign and IRS are the two main malaria vector control strategies in Senegal and sub-Saharan Africa generally [29, 30, 15] with the main goals to reduced host-vector contact and vector population longevity. Several authors have reported the possible involvement of An. arabiensis, An. melas and An. coluzzii species, possibly playing a main role in malaria transmission in the study area here [31, 25, 12]. The absence of infected females of An. coluzzii during the current study could be explained by the low sample representativity of this species during the study period. The average EIR for An. arabiensis and An. melas almost seven time higher for the first species than the latter without significant difference due to the low numbers of An. melas, being nevertheless lower than reported previously in same the area with 13.14 infective bites per person per year [12]. This low level of transmission as observed here is probably related to a variety of malaria control interventions implemented by the NMCP in this area. Indeed, a Seasonal Malaria Chemoprevention (SMC) in children under ten years of age was implemented in the area between 2008 and 2011, followed by two targeted indoor residual spraying campaigns with pirimiphos-methyl in 2013 and 2014 [13, 15].

This study demonstrated the predominance and the involvement of both An. arabienis and An. melas in maintaining malaria in hotspot found in an overall low malaria transmission in the central western Senegal. The findings generated on infection using a sensitive qPCR approach, which allows the detection of low plasmodial infection in mosquitoes, suitable for areas of low malaria transmission. The data generated will be shared with the PNLP and will certainly allow to better tailor the monitoring of malaria in this area, eligible for malaria elimination. Subsequent investigations on insecticide phenotypic resistance and intensity for these two species in the area, are needed to better complement evidence to better selected and target vector control strategies to drive toward the goal of malaria elimination as aimed by the NMCP in eligible areas.

IRS

indoor residual spraying

WHO

world health organization

LLIN

long lasting insecticidal nets

NMCP

national malaria control program

PNLP

Programme National de Lutte contre le Paludisme

HLC

human landing catches

PSC

Pyrethrum Spray Catches

PCR

polymerase chain reaction

COVID-19

Coronavirus disease 2019

SMC

seasonal malaria chemoprevention

HBR

human-biting rate

EIR

entomological inoculation rate

IRD

Indoor Resting Density

HBR

human biting rate

GLM

generalized linear model.

Acknowledgments

The authors of this paper wish to express their gratitude to the Ministry of Health, the NMCP. We are also grateful to the villagers of Diofior, Keur Martin and Mbine coly for their cooperation.

Authors' contributions

Conceptualization: O.S.; L.K., E.A.N. and O.F.; Data curation: O.S.; M.A.N., P.C.S. and E.A.N; Formal analysis: O.S.; E.A.N., and D.W; Funding acquisition: O.G. and O.F. ; Investigation: O.S., P.C.S., A.N., M.A.N.,. and E.A.N.; Methodology: O.S., DW, O.F, M.J.D., L.K. and E.A.N., Project administration: O.S., O.G. and O.F.; Supervision: D.W., M.J.D., O.F., L.K. and O.G. Validation: D.W., O.S., M.J.D., O.F., L.K. and E.A.N; Writing—original draft: O.SY and E.A.N Writing—review and editing: O.SY, P.C.S., A.N., M.A.N., D.W., O.F, M.J.D., O.G., LK., O.G., B.S.A and. E.A.N. All authors have read and agreed to the published version of the manuscript.

Funding information

This research was funded in whole, or in part, by the Wellcome Trust [WT: 107741/A/15/Z] and the UK Foreign, Commonwealth & Development Office, with support from the Developing Excellence in Leadership, Training and Science in Africa (DELTAS Africa) programme. For the purpose of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission.

Compliance with ethical standards

Ethics approval and consent to participate This study was approved by the Ethics Committee of University Cheikh Anta Diop of Dakar, Senegal.

Declaration of Competing Interests

The authors declare that they have no competing interests.

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No competing interests reported.

Residual malaria transmission in central-western Senegal: role and bionomics of the local populations of Anopheles arabiensis and Anopheles melas

Status:

Version 1

Abstract

Figures

Introduction

Data Analysis

Results

Discussion

Conclusion

Abbreviations

Declarations