Environmental impact of tsetse eradication in Senegal.

The sterile insect technique is an environment friendly control tactic and is very species specific. It is not a stand-alone technique and has been used mostly in combination with other control tactics within an area-wide integrated pest management strategy. For a period of eight years, the direct impact of a campaign to eradicate a population of the tsetse fly Glossina palpalis gambiensis in Senegal was monitored using a set of fruit-feeding insect species (Cetoniinae and Nymphalidae) that served as ecological indicators of the health of the ecosystem. Here we show that the eradication campaign had very limited impacts on the apparent densities of the most frequent species as well as three diversity indexes during the reduction phase involving insecticides but reverted to pre-intervention levels as soon as the release of the sterile male insects started. These results greatly expand our understanding of the impact of vector eradication campaigns on non-target species.

Ecological distribution and population dynamics of Rift Valley fever virus mosquito vectors (Diptera, Culicidae) in Senegal.

BACKGROUND: Many zoonotic infectious diseases have emerged and re-emerged over the last two decades. There has been a significant increase in vector-borne diseases due to climate variations that lead to environmental changes favoring the development and adaptation of vectors. This study was carried out to improve knowledge of the ecology of mosquito vectors involved in the transmission of Rift Valley fever virus (RVFV) in Senegal. METHODS: An entomological survey was conducted in three Senegalese agro-systems, Senegal River Delta (SRD), Senegal River Valley (SRV) and Ferlo, during the rainy season (July to November) of 2014 and 2015. Mosquitoes were trapped using CDC light traps set at ten sites for two consecutive nights during each month of the rainy season, for a total of 200 night-traps. Ecological indices were calculated to characterize the different populations of RVFV mosquito vectors. Generalized linear models with mixed effects were used to assess the influence of climatic conditions on the abundance of RVFV mosquito vectors. RESULTS: A total of 355,408 mosquitoes belonging to 7 genera and 35 species were captured in 200 night-traps. RVFV vectors represented 89.02% of the total, broken down as follows: Ae. vexans arabiensis (31.29%), Cx. poicilipes (0.6%), Cx. tritaeniorhynchus (33.09%) and Ma. uniformis (24.04%). Comparison of meteorological indices (rainfall, temperature, relative humidity), abundances and species diversity indicated that there were no significant differences between SRD and SRV (P = 0.36) while Ferlo showed significant differences with both (P < 0.001). Mosquito collection increased significantly with temperature for Ae. vexans arabiensis (P < 0.001), Cx. tritaeniorhynchus (P = 0.04) and Ma. uniformis (P = 0.01), while Cx. poicilipes decreased (P = 0.003). Relative humidity was positively and significantly associated with the abundances of Ae. vexans arabiensis (P < 0.001), Cx. poicilipes (P = 0.01) and Cx. tritaeniorhynchus (P = 0.007). Rainfall had a positive and significant effect on the abundances of Ae. vexans arabiensis (P = 0.005). The type of biotope (temporary ponds, river or lake) around the trap points had a significant effect on the mosquito abundances (P < 0.001). CONCLUSIONS: In terms of species diversity, the SRD and SRV ecosystems are similar to each other and different from that of Ferlo. Meteorological indices and the type of biotope (river, lake or temporary pond) have significant effects on the abundance of RVFV mosquito vectors.

Insight on the larval habitat of Afrotropical Culicoides Latreille (Diptera: Ceratopogonidae) in the Niayes area of Senegal, West Africa.

BACKGROUND: Certain biting midges species of the genus Culicoides (Diptera: Ceratopogonidae) are vectors of virus to livestock worldwide. Culicoides larval ecology has remained overlooked because of difficulties to identify breeding sites, methodological constraints to collect samples and lack of morphological tools to identify field-collected individuals to the species level. After the 2007 unforeseen outbreaks of African horse sickness virus (AHSV) in Senegal (West Africa), there is a need to identify suitable and productive larval habitats in horse farms for the main Culicoides species to evaluate the implementation of vector control measures or preventive actions. METHODS: We investigate twelve putative larval habitats (habitat types) of Culicoides inside and outside of three horse farms in the Niayes area of Senegal using a combination of flotation and emergence methods during four collection sessions. RESULTS: Among the three studied horse farms, three habitat types were found positive for Culicoides larvae: pond edge, lake edge and puddle edge. A total of 1420 Culicoides individuals (519♂/901♀) belonging to ten species emerged from the substrate samples. Culicoides oxystoma (40 %), C. similis (25 %) and C. nivosus (24 %) were the most abundant species and emerged from the three habitat types while C. kingi (5 %) was only retrieved from lake edges and one male emerged from puddle edge. Culicoides imicola (1.7 %) was found in low numbers and retrieved only from pond and puddle edges. CONCLUSIONS: Larval habitats identified were not species-specific. All positive larval habitats were found outside the horse farms. This study provides original baseline information on larval habitats of Culicoides species in Senegal in an area endemic for AHSV, in particular for species of interest in animal health. These data will serve as a point of reference for future investigations on larval ecology and larval control measures.

Host preferences and circadian rhythm of Culicoides (Diptera: Ceratopogonidae), vectors of African horse sickness and bluetongue viruses in Senegal.

African horse sickness- and bluetongue virus are orbiviruses transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) to horses and to ruminants, respectively. Since the last epizootic outbreak of African horse sickness in 2007 in Senegal, extensive investigations have been undertaken to improve our knowledge on Culicoides species involved locally in the transmission of the virus. The purpose of this study was to compare and quantify the host preferences of potential vectors of these orbiviruses on horse and sheep and to study their circadian rhythm. We found that Culicoides oxystoma and species of the sub-genus Avaritia (Culicoides imicola, Culicoides bolitinos and Culicoides pseudopallidipennis) had a preference for horse when compared to sheep (the predicted ratio between horse and sheep was 80 for C. oxystoma and 26 for C. imicola), and were mostly crepuscular: C. oxystoma had continuous activity throughout the diel with peaks in numbers collected after sunrise and sunset, while C. imicola was mostly nocturnal with peak after sunset. Unexpectedly, species of the subgenus Lasiohelea was also collected during this study. This diurnal biting species was a nuisance pest for both animal species used as bait.

Circadian activity of Culicoides oxystoma (Diptera: Ceratopogonidae), potential vector of bluetongue and African horse sickness viruses in the Niayes area, Senegal.

Culicoides biting midges (Diptera: Ceratopogonidae) are important vectors of arboviruses in Africa. Culicoides oxystoma has been recently recorded in the Niayes region of Senegal (West Africa) and its high abundance on horses suggests a potential implication in the transmission of the African horse sickness virus in this region. This species is also suspected to transmit bluetongue virus to imported breeds of sheep. Little information is available on the biology and ecology of Culicoides in Africa. Therefore, understanding the circadian host-seeking activity of this putative vector is of primary importance to assess the risk of the transmission of Culicoides-borne pathogens. To achieve this objective, midges were collected using a sheep-baited trap over two consecutive 24-h periods during four seasons in 2012. A total of 441 Culicoides, belonging to nine species including 418 (94.8%) specimens of C. oxystoma, were collected. C. oxystoma presented a bimodal circadian host-seeking activity at sunrise and sunset in July and was active 3 h after sunrise in April. Daily activity appeared mainly related to time periods. Morning activity increased with the increasing temperature up to about 27 °C and then decreased with the decreasing humidity, suggesting thermal limits for C. oxystoma activity. Evening activity increased with the increasing humidity and the decreasing temperature, comprised between 20 and 27 °C according to seasons. Interestingly, males were more abundant in our sampling sessions, with similar activity periods than females, suggesting potential animal host implication in the facilitation of reproduction. Finally, the low number of C. oxystoma collected render practical vector-control recommendations difficult to provide and highlight the lack of knowledge on the bio-ecology of this species of veterinary interest.

Culicoides (Diptera: Ceratopogonidae) midges, the vectors of African horse sickness virus--a host/vector contact study in the Niayes area of Senegal.

BACKGROUND: African horse sickness (AHS) is an equine disease endemic to Senegal. The African horse sickness virus (AHSV) is transmitted to the mammalian hosts by midges of the Culicoides Latreille genus. During the last epizootic outbreak of AHS in Senegal in 2007, 1,169 horses died from this disease entailing an estimated cost of 1.4 million euros. In spite of the serious animal health and economic implications of AHS, very little is known about determinants involved in transmission such as contact between horses and the Culicoides species suspected of being its vectors. METHODS: The monthly variation in host/vector contact was determined in the Niayes area, Senegal, an area which was severely affected by the 2007 outbreak of AHS. A horse-baited trap and two suction light traps (OVI type) were set up at each of five sites for three consecutive nights every month for one year. RESULTS: Of 254,338 Culicoides midges collected 209,543 (82.4%) were female and 44,795 (17.6%) male. Nineteen of the 41 species collected were new distribution records for Senegal. This increased the number of described Culicoides species found in Senegal to 53. Only 19 species, of the 41 species found in light trap, were collected in the horse-baited trap (23,669 specimens) largely dominated by Culicoides oxystoma (22,300 specimens, i.e. 94.2%) followed by Culicoides imicola (482 specimens, i.e. 2.0%) and Culicoides kingi (446 specimens, i.e. 1.9%). CONCLUSIONS: Culicoides oxystoma should be considered as a potential vector of AHSV in the Niayes area of Senegal due to its abundance on horses and its role in the transmission of other Culicoides-borne viruses.

Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal.

Tsetse flies are vectors of human and animal trypanosomoses in sub-Saharan Africa and are the target of the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). Glossina palpalis gambiensis (Diptera: Glossinidae) is a riverine species that is still present as an isolated metapopulation in the Niayes area of Senegal. It is targeted by a national eradication campaign combining a population reduction phase based on insecticide-treated targets (ITTs) and cattle and an eradication phase based on the sterile insect technique. In this study, we used species distribution models to optimize control operations. We compared the probability of the presence of G. p. gambiensis and habitat suitability using a regularized logistic regression and Maxent, respectively. Both models performed well, with an area under the curve of 0.89 and 0.92, respectively. Only the Maxent model predicted an expert-based classification of landscapes correctly. Maxent predictions were therefore used throughout the eradication campaign in the Niayes to make control operations more efficient in terms of deployment of ITTs, release density of sterile males, and location of monitoring traps used to assess program progress. We discuss how the models' results informed about the particular ecology of tsetse in the target area. Maxent predictions allowed optimizing efficiency and cost within our project, and might be useful for other tsetse control campaigns in the framework of the PATTEC and, more generally, other vector or insect pest control programs.

First record of Culicoides oxystoma Kieffer and diversity of species within the Schultzei group of Culicoides Latreille (Diptera: Ceratopogonidae) biting midges in Senegal.

The Schultzei group of Culicoides Latreille (Diptera: Ceratopogonidae) is distributed throughout Africa to northern Asia and Australasia and includes several potential vector species of livestock pathogens. The taxonomy of the species belonging to this species group is confounded by the wide geographical distribution and morphological variation exhibited by many species. In this work, morphological and molecular approaches were combined to assess the taxonomic validity of the species and morphological variants of the Schultzei group found in Senegal by comparing their genetic diversity with that of specimens from other geographical regions. The species list for Senegal was updated with four species: Culicoides kingi, C. oxystoma, C. enderleini and C. nevilli being recorded. This is the first record of C. oxystoma from Africa south of Sahara, and its genetic relationship with samples from Israel, Japan and Australia is presented. This work provides a basis for ecological studies of the seasonal and spatial dynamics of species of this species group that will contribute to better understanding of the epidemiology of the viruses they transmit.

Population genetics as a tool to select tsetse control strategies: suppression or eradication of Glossina palpalis gambiensis in the Niayes of Senegal.

BACKGROUND: The Government of Senegal has initiated the "Projet de lutte contre les glossines dans les Niayes" to remove the trypanosomosis problem from this area in a sustainable way. Due to past failures to sustainably eradicate Glossina palpalis gambiensis from the Niayes area, controversies remain as to the best strategy implement, i.e. "eradication" versus "suppression." To inform this debate, we used population genetics to measure genetic differentiation between G. palpalis gambiensis from the Niayes and those from the southern tsetse belt (Missira). METHODOLOGY/PRINCIPAL FINDINGS: Three different markers (microsatellite DNA, mitochondrial CO1 DNA, and geometric morphometrics of the wings) were used on 153 individuals and revealed that the G. p. gambiensis populations of the Niayes were genetically isolated from the nearest proximate known population of Missira. The genetic differentiation measured between these two areas (theta = 0.12 using microsatellites) was equivalent to a between-taxa differentiation. We also demonstrated that within the Niayes, the population from Dakar - Hann was isolated from the others and had probably experienced a bottleneck. CONCLUSION/SIGNIFICANCE: The information presented in this paper leads to the recommendation that an eradication strategy for the Niayes populations is advisable. This kind of study may be repeated in other habitats and for other tsetse species to (i) help decision on appropriate tsetse control strategies and (ii) find other possible discontinuities in tsetse distribution.