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Background African animal trypanosomosis (AAT), transmitted by tsetse flies, is arguably the main disease constraint to integrated crop-livestock agriculture in sub-Saharan Africa, and African heads of state and governments adopted a resolution to rid the continent of this scourge. In order to sustainably reduce or eliminate the burden of AAT, a progressive and evidence-based approach is needed, which must hinge on harmonized, spatially explicit information on the occurrence of AAT and its vectors. Methods A digital repository was assembled, containing tsetse and AAT data collected in Burkina Faso between 1990 and 2019. Data were collected either in the framework of control activities or for research purposes. Data were systematically verified, harmonized, georeferenced and integrated into a database (PostgreSQL). Entomological data on tsetse were mapped at the level of individual monitoring traps. When this was not possible, mapping was done at the level of site or location. Epidemiological data on AAT were mapped at the level of location or village. Results Entomological data showed the presence of four tsetse species in Burkina Faso. Glossina tachinoides, present from the eastern to the western part of the country, was the most widespread and abundant species (56.35% of the catches). Glossina palpalis gambiensis was the second most abundant species (35.56%), and it was mainly found in the west. Glossina morsitans submorsitans was found at lower densities (6.51%), with a patchy distribution in the southern parts of the country. A single cluster of G. medicorum was detected (less than 0.25%), located in the south-west. Unidentified tsetse flies accounted for 1.33%. For the AAT component, data for 54,948 animal blood samples were assembled from 218 geographic locations. The samples were tested with a variety of diagnostic methods. AAT was found in all surveyed departments, including the tsetse-free areas in the north. Trypanosoma vivax and T. congolense infections were the dominant ones, with a prevalence of 5.19 ± 18.97% and 6.11 ± 21.56%, respectively. Trypanosoma brucei infections were detected at a much lower rate (0.00 ± 0.10%). Conclusions The atlas provides a synoptic view of the available information on tsetse and AAT distribution in Burkina Faso. Data are very scanty for most of the tsetse-free areas in the northern part of the country. Despite this limitation, this study generated a robust tool for targeting future surveillance and control activities. The development of the atlas also strengthened the collaboration between the different institutions involved in tsetse and AAT research and control in Burkina Faso, which will be crucial for future updates and the sustainability of the initiative. Graphical Abstract

Studying isolation by distance can provide useful demographic information. To analyze isolation by distance from molecular data, one can use some kind of genetic distance or coalescent simulations. Molecular markers can often display technical caveats, such as PCR-based amplification failures (null alleles, allelic dropouts). These problems can alter population parameter inferences that can be extracted from molecular data. In this simulation study, we analyze the behavior of different genetic distances in Island (null hypothesis) and stepping stone models displaying varying neighborhood sizes. Impact of null alleles of increasing frequency is also studied. In stepping stone models without null alleles, the best statistic to detect isolation by distance in most situations is the chord distance DCSE. Nevertheless, for markers with genetic diversities H-S

International audience; Tsetse flies are the cyclical vectors of African animal trypanosomosis (AAT) and human African trypanosomosis (HAT). In March 2010, the Government of Ghana initiated a large scale integrated tsetse eradication campaign in the Upper West Region (UWR) (approximate to 18,000 km(2)) under the umbrella of the Pan-African Tsetse and Trypanosomosis Eradication Campaign (PATTEC). We investigated the structuring of Glossina tachinoides populations within and between the three main river basins of the target area in the UWR. Out of a total sample of 884 flies, a sub-sample of 266 was genotyped at nine microsatellite loci. The significance of the different hierarchical levels was tested using Yang's parameters estimated with Weir and Cockerham's method. A significant effect of traps within groups (pooling traps no more than 3 km distant from each other), of groups within river basins and of river basins within the whole target area was observed. Isolation by distance between traps was highly significant. A local density of 0.48-0.61 flies/m(2) was estimated and a dispersal distance that approximated 11 m per generation [CI 9, 17]. No significant sex-biased dispersal was detected. Dispersal distances of G. tachinoides in the UWR were relatively low, possibly as a result of the fragmentation of the habitat and the seasonality of the Kulpawn and Sissili rivers. Moreover, very high fly population densities were observed in the sample sites, which potentially reduces dispersal at constant habitat saturation, because the probability that migrants can established is reduced (density dependent dispersal). However, the observed spatial dispersal was deemed sufficient for a G. tachinoides-cleared area to be reinvaded from neighboring populations in adjacent river basins. These data corroborate results from other population genetics studies in West Africa, which indicate that G. tachinoides populations from different river basins cannot be considered isolated.

International audience; The increase of human population, combined with climatic changes, contributed to the modification of spatial distribution of tsetse flies, main vector of trypanosomiasis. In order to establish and compare tsetse presence and their relationship with vegetation, entomological survey was performed using biconical traps deployed in transects, simultaneously with phyto-sociological study, on the Comoe river at its source in the village of Moussodougou, and in the semi-protected area of Folonzo, both localities in Southern Burkina Faso. In Folonzo, the survey revealed a diversity of tsetse with 4 species occurring with apparent densities as follows: Glossina tachinoides (8.9 tsetse/trap/day); G. morsitans submorsitans (1.8 tsetse/trap/day); G. palpalis gambiensis (0.6/trap/day) and G. medicorum (0.15 tsetse/trap/day). In Moussodougou, a highly anthropized area, mainly G. p. gambiensis was caught (2.06 tsetse/trap/day), and rarely G. tachinoides. The phyto-sociological study allowed discrimination of 6 types of vegetation in both localities, with 3 concordances that are riparian forest, shrubby and woody savannah. In Moussodougou, all tsetse were caught in the riparian forest. That was also the case in Folonzo where a great proportion (95 to 99 % following the season) of G. p. gambiensis and G. tachinoides were caught in the gallery, while G. m. submorsitans was occurring as well in the gallery as in the savannah, and G. medicorum in the forest gallery. This study showed that although G. tachinoides and G.p. gambiensis are both riparian, they do not have the same preference in terms of biotope.

International audience; Isolated tsetse populations constitute a target for tsetse control programmes in endemic countries, since their isolation, if demonstrated, allows control without reinvasion risk from neighbouring populations. Population genetic parameters, such as the fixation index, have proven useful to assess isolation status, and should also give important information on the divergence time since isolation. We gathered results obtained from different datasets regarding several examples of putatively totally isolated tsetse populations of different tsetse species: Glossina palpalis gambiensis in Guinea, in the Niayes of Senegal, and in the sacred wood of Bama in Burkina Faso; G. tachinoides from Bitou and Pama in South-East Burkina Faso. The different levels of isolation were compared to differentiation between the two subspecies G. p. gambiensis and G. p. palpalis which both occur allopatrically along the Comoe River in Ivory Coast. We also use some historical evidence to calibrate differentiation speed and give estimates of time since separation for the different cases studied. Discrepancies mostly come from underestimate of effective population sizes, and we propose improving sampling design and genetic markers quality to circumvent such caveats.

La technique PCR (polymerase chain reaction) a été utilisée pour l'identificat-ion des trypanosomes chez des glossines et des bovins infectés provenant de la zone d'aménagement pastoral de Yalé, au sud du Burkina Faso. Sur les 84 intestins moyens parasitologiquement positifs de Glossina tachinoides qui ont été analysés, 50 ont pu être identifiés par PCR (Trypanosoma congolens-e types « savane » et « forêt », T. simiae et T. vivax). Chez les bovins, la technique PCR a révélé la prédominance de T. congolense « savane » et de T. vivax. Le taxon « forêt » de T. congolense n'a pas été détecté chez le bétail. Certains animaux aparasitémiques mais suspects ont montré des signaux positifs par PCR avec les amorces spécifiques de T. congolense « savane ». Ces résultats confirment le haut intérêt de la technique PCR pour révéler les pauci-infections et les infections mixtes chez les différents hôte et mettre en évidence des relations complexes d'affinité des taxons « savane » et« forêt » de T. congolense vis-à-vis de leurs vecteurs, mais aussi vis-à-vis de leurs hôtes vertébrés.

International audience; Background: In Chad, several species of tsetse flies (Genus: Glossina) transmit African animal trypanosomoses (AAT), which represents a major obstacle to cattle rearing, and sleeping sickness, which impacts public health. After the failure of past interventions to eradicate tsetse, the government of Chad is now looking for other approaches that integrate cost-effective intervention techniques, which can be applied by the stake holders to control tsetse-transmitted trypanosomoses in a sustainable manner. The present study thus attempted to assess the efficacy of restricted application of insecticides to cattle leg extremities using footbaths for controlling Glossina m. submorsitans, G. tachinoides and G. f. fuscipes in southern Chad. Methodology/Principal Findings: Two sites were included, one close to the historical human African trypanosomiasis (HAT) focus of Moundou and the other to the active foci of Bodo and Moissala. At both sites, a treated and an untreated herd were compared. In the treatment sites, cattle were treated on a regular basis using a formulation of deltamethrin 0.005% (67 to 98 cattle were treated in one of the sites and 88 to 102 in the other one). For each herd, tsetse densities were monthly monitored using 7 biconical traps set along the river and beside the cattle pen from February to December 2009. The impact of footbath treatment on tsetse populations was strong (p < 10(-3)) with a reduction of 80% in total tsetse catches by the end of the 6-month footbath treatment. Conclusions/Significance: The impact of footbath treatment as a vector control tool within an integrated strategy to manage AAT and HAT is discussed in the framework of the "One Health" concept. Like other techniques based on the treatment of cattle, this technology should be used under controlled conditions, in order to avoid the development of insecticide and acaricide resistance in tsetse and tick populations, respectively.

Following the discovery of four cases of African human trypanosomiasis, an entomological survey was conducted along the Mouhoun river in southwest Burkina Faso to collect Glossina palpalis gambiensis and G.tachinoides. Among 226 flies dissected, 4.87% (eleven individuals) were infected in midgut or proboscis, but never in the salivary glands. Polymerase chain reaction analysis was undertaken, and was able to characterize all the proboscis infections, and half of the midgut infections. Only Trypanosoma simiae and T. vivax were found in the organs of infected flies, in single or mixed-species infections. Ten more flies, negative with parasitological examination, were tested with Trypanozoon primers and remained negative. The epidemiological significance of the absence of T.brucei group infections in wild tsetse populations and the presence of T.simiae in G.p.gambiensis are discussed.

Cent quatre vingt-deux Glossina tachinoides ont ete infectees avec Trypanosoma congolense type "savane". Les taux d'infection ont ete evalues par examen microscopique et par PCR. L'emission des trypanosomes par salivation provoquee a ete etudiee selon differentes techniques de detection des parasites qui ont ete comparees. Les resultats des dissections ont revele un fort pourcentage d'infections immatures. La technique PCR appliquee sur les proboscis a confirme les resultats parasitologiques. Les experiences de salivation ont montre une grande variabilite, inter et infra-individuelle, dans l'emission des trypanosomes lors des sondages. La technique PCR a ete equivalente a l'examen microscopique pour detecter les trypanosomes dans les salivats. La methode de xenodiagnostic inverse s'est revelee la moins performante des trois pour detecter les glossines infectantes. L'ensemble de ces resultats a permis de preciser la capacite vectorielle de G. tachinoides vis-a-vis de T. congolense type "savane" au laboratoire, et de donner des elements supplementaires de comprehension au role de cette glossine dans l'epidemiologie de la maladie. (Resume d'auteur)

The prohing and salivation behaviour on a warm slide of three tsetse fly species or subspecies (Glossina morsitans morsitans, Glossina palpalis gambiensis, Glossina tachinoides) was examined with respect to various parameters (species, sex, age, starvation period, trypanosome infection, quality of support). Each fly was given the opportunity to probe the warm slide (38°C) for 5 minutes (we mean by probing an attempt to touch the glass slide by the proboscis in a biting position). G. m. morsitans is by far the most efficient at probing (70.50 %) when compared with G. tachinoides (50.50 %) and G. palpalis gambiensis (45.80 %). Globally, males (61.30 %) are more active than females (52 %) and those of the morsitans group are more active than those of the palpalis group. Teneral flies probe more easily than non-teneral flies, with an increased advantage in G. m. morsitans. The starvation period increases the probing behaviour, but at 48 h, G. m. morsitans probed as much as G. palpalis gambiensis and G. tachinoides at 72 h. The males of G. m. morsitans and G. palpalis gambiensis are more precocious than females, but the inverse is observed in G. tachinoides. Infection by T. congolense (EATRO 325 strain) does not affect the probing behaviour of males of all 3 species but seems to lower that of females in the palpalis group. Addition of a drop of PSG or blood improves the probing behaviour of infected G. m. morsitans females (the only ones tested). The results are discussed in relation to biological data and knowledge of the receptor systems of tsetse flies.

Background An integrated strategy of intervention against tsetse flies was implemented in the Upper West Region of Ghana (9.62°–11.00° N, 1.40°–2.76° W), covering an area of ≈18,000 km2 within the framework of the Pan-African Tsetse and Trypanosomosis Eradication Campaign. Two species were targeted: Glossina tachinoides and Glossina palpalis gambiensis. Methodology/Principal Findings The objectives were to test the potentiality of the sequential aerosol technique (SAT) to eliminate riverine tsetse species in a challenging subsection (dense tree canopy and high tsetse densities) of the total sprayed area (6,745 km2) and the subsequent efficacy of an integrated strategy including ground spraying (≈100 km2), insecticide treated targets (20,000) and insecticide treated cattle (45,000) in sustaining the results of tsetse suppression in the whole intervention area. The aerial application of low-dosage deltamethrin aerosols (0.33–0.35 g a.i/ha) was conducted along the three main rivers using five custom designed fixed-wings Turbo thrush aircraft. The impact of SAT on tsetse densities was monitored using 30 biconical traps deployed from two weeks before until two weeks after the operations. Results of the SAT monitoring indicated an overall reduction rate of 98% (from a pre-intervention mean apparent density per trap per day (ADT) of 16.7 to 0.3 at the end of the fourth and last cycle). One year after the SAT operations, a second survey using 200 biconical traps set in 20 sites during 3 weeks was conducted throughout the intervention area to measure the impact of the integrated control strategy. Both target species were still detected, albeit at very low densities (ADT of 0.27 inside sprayed blocks and 0.10 outside sprayed blocks). Conclusions/Significance The SAT operations failed to achieve elimination in the monitored section, but the subsequent integrated strategy maintained high levels of suppression throughout the intervention area, which will contribute to improving animal health, increasing animal production and fostering food security., Author Summary We document the impact of an integrated strategy of intervention against riverine tsetse flies in the Upper West Region of Ghana within the framework of the Pan-African Tsetse and Trypanosomosis Eradication Campaign, in an area of ≈18,000 km2. The strategy included a sequential aerosol technique (SAT) component, i.e. four applications of low-dosage deltamethrin aerosols, conducted along the three main rivers. The impact of SAT on tsetse densities was monitored in a challenging subsection (dense tree canopy and high tsetse densities) from two weeks before until two weeks after the operations. The SAT operations succeeded in reducing tsetse populations by 98% within one month but fell short of achieving elimination. Insecticide ground spraying, deltamethrin-treated targets and cattle were used as complementary tools to maintain tsetse suppression in the intervention area. An entomological survey conducted one year after SAT operations showed that both target species were still present, albeit at drastically reduced densities as compared to the baseline levels. This integrated strategy of intervention will contribute to improving animal health, increasing animal production and fostering food security in the target area.

International audience; In the Mouhoun River basin, Burkina Faso, the main vectors of African animal trypanosomoses are Glossina palpalis gambiensis Vanderplank and Glossina tachinoides Westwood (Diptera: Glossinidae), both of which are riverine tsetse species. The aim of our study was to understand the impact of landscape anthropogenic changes on the seasonal dynamics of vectors and associated trypanosomosis risk. Three sites were selected on the basis of the level of disturbance of tsetse habitats and predominant tsetse species: disturbed (Boromo, for G. tachinoides) and half-disturbed (Douroula for G. tachinoides and Kadomba for G. p. gambiensis). At each of these sites, seasonal variations in the apparent densities of tsetse and mechanical vectors and tsetse infection rates were monitored over 17 months. Tsetse densities differed significantly between sites and seasons. Of 5613 captured tsetse, 1897 were dissected; 34 of these were found to be infected with trypanosomes. The most frequent infection was Trypanosoma vivax (1.4%), followed by Trypanosoma congolense (0.3%) and Trypanosoma brucei (0.05%). The mean physiological age of 703 tsetse females was investigated to better characterize the transmission risk. Despite the environmental changes, it appeared that tsetse lived long enough to transmit trypanosomes, especially in half-disturbed landscapes. A total of 3021 other biting flies from 15 species (mainly Tabanidae and Stomoxyinae) were also caught: their densities also differed significantly among sites and seasons. Their relative importance regarding trypanosome transmission is discussed; the trypanosomosis risk in cattle was similar at all sites despite very low tsetse densities (but high mechanical vector densities) in one of them.

Background African animal trypanosomosis is a major obstacle to the development of more efficient and sustainable livestock production systems in West Africa. Riverine tsetse species such as Glossina palpalis gambiensis Vanderplank and Glossina tachinoides Westwood are the major vectors. A wide variety of control tactics is available to manage these vectors, but their removal will in most cases only be sustainable if the control effort is targeting an entire tsetse population within a circumscribed area. Methodology/Principal Findings In the present study, genetic variation at microsatellite DNA loci was used to examine the population structure of G. p. gambiensis and G. tachinoides inhabiting four adjacent river basins in Burkina Faso, i.e. the Mouhoun, the Comoé, the Niger and the Sissili River Basins. Isolation by distance was significant for both species across river basins, and dispersal of G. tachinoides was ∼3 times higher than that of G. p. gambiensis. Thus, the data presented indicate that no strong barriers to gene flow exists between riverine tsetse populations in adjacent river basins, especially so for G. tachinoides. Conclusions/Significance Therefore, potential re-invasion of flies from adjacent river basins will have to be prevented by establishing buffer zones between the Mouhoun and the other river basin(s), in the framework of the PATTEC (Pan African Tsetse and Trypanosomosis Eradication Campaign) eradication project that is presently targeting the northern part of the Mouhoun River Basin. We argue that these genetic analyses should always be part of the baseline data collection before any tsetse control project is initiated., Author Summary Tsetse flies are insects that transmit trypanosomes to humans (sleeping sickness) and animals (nagana). Controlling these vectors is a very efficient way to control these diseases. In Burkina Faso, a tsetse eradication campaign is presently targeting the northern part of the Mouhoun River Basin. To attain this objective, the approach has to be area-wide, i.e. the control effort targets an entire pest population within a circumscribed area. To assess the level of this isolation, we studied the genetic structure of Glossina palpalis gambiensis and Glossina tachinoides populations in the target area and in the adjacent river basins of the Comoé, the Niger and the Sissili River Basins. Our results suggest an absence of strong genetic isolation of the target populations. We therefore recommend establishing permanent buffer zones between the Mouhoun and the other river basin(s) to prevent reinvasion. This kind of study may be extended to other areas on other tsetse species.

International audience; The impact of landscape fragmentation resulting from human- and climate-mediated factors on the structure of a population of Glossina tachinoides Westwood (Diptera: Glossinidae) in the Mouhoun River basin, Burkina Faso, was investigated. Allele frequencies at five microsatellite loci were compared in four populations. The average distance between samples was 72 km. The sampling points traversed an ecological cline in terms of rainfall and riverine forest ecotype, along a river loop that enlarged from upstream to downstream. Microsatellite DNA demonstrated no structuring among the groups studied (F(ST) = 0.015, P = 0.07), which is contrary to findings pertaining to Glossina palpalis gambiensis Vanderplank in the same geographical area. The populations of G. tachinoides showed complete panmixia (F(IS) = 0, P = 0.5 for the whole sample) and no genetic differentiation among populations or global positioning system trap locations. This is in line with the results of dispersal studies which indicated higher diffusion coefficients for G. tachinoides than for G. p. gambiensis. The impact of these findings is discussed within the framework of control campaigns currently promoted by the Pan African Tsetse and Trypanosomosis Eradication Campaign.

African animal trypanosomoses are the main parasitological constraints to livestock production in many sub-Saharan African countries infested with tsetse flies. A prospective survey was implemented in Dafinso (Burkina Faso) to assess the effect of deltamethrin 0.005% (VectocidND, CEVA Sante´ Animale) impregnation of cattle on trypanosomes transmission in cattle. Two herds were involved in the survey. They were watered at two different waterpoints located on the same river harboring a Guinean riparian forest infested with two different species of tsetse flies (Diptera: Glossinidae), Glossina palpalis gambiensis Vanderplank and G. tachinoides Westwood. Animals belonging to one of the herds were impregnated with deltamethrin applied with a footbath whereas the other herd was used as control. The overall incidence of cattle trypanosomoses was reduced (p = 0.01) from 0.76 (control group) to 0.11 (footbath-treated group). A positive effect of the footbath treatment on packed-cell volume was observed (p < 0.001). The conditions requested to use a footbath to prevent cattle trypanosomoses are discussed.

African animal trypanosomosis is a major pathological constraint to cattle breeding across 10 million km2 of sub-Saharan West African countries infested by tsetse flies, their cyclic vectors. The release of sterile males (sterile insect technique [SIT]) is a potentially important control technique aimed at eliminating the vectors. Prior to release, tsetse are generally treated with isometamidium chloride, a trypanocide, to prevent them from transmitting parasites. The present study investigated the preventive action of isometamidium chloride (0.5 mg/L) on the subsequent susceptibility of tsetse released into the wild. A total of 1755 Glossina palpalis gambiensis Vanderplank and 744 Glossina tachinoides Westwood were released, of which 50 and 48, respectively, were recaptured 22?43 days after release. Their probosces were analysed by polymerase chain reaction to identify mature infections with three trypanosome species (Trypanosoma vivax, Trypanosoma brucei sensu lato and Trypanosoma congolense savannah type). Two mature infections with T. vivax and four with T. congolense were detected, indicating that the use of this treatment regimen in an SIT campaign would not totally prevent sterile males from transmitting trypanosomes. (Resume d'auteur)

In Burkina Faso, we assessed the efficacy of treating cattle with a footbath containing aqueous formulations of pyrethroids to control two tsetse-fly species, Glossina tachinoides Westwood, 1850 (Diptera, Glossinidae) and Glossina palpalis gambiensis Vanderplank 1949. Legs were the most targeted parts of the body for tsetse-fly blood meals: 81% (95% CI: 73, 89) for G. tachinoides and 88% (81, 95) for G. palpalis. The in-stable efficacy of footbath treatments was compared with manual full spraying with a 0.005% alphacypermethrin (Dominex, FMC, Philadelphia, USA) formulation (250 mL versus 2 L). The proportions of knocked-down flies were the same with footbath and full spray but the latter was more protective against fly bites. In field use, the efficacy of both methods should be similar given the recommended treatment frequency: 3 days for footbath versus 7 days for full spray. Among 96 cattle drinking at the same water point in Dafinso (Burkina Faso), 68 (71%) were treated with a footbath containing a 0.005% deltamethrin formulation (Vectocid, CEVA SA, Libourne, France). We observed the effect of this live-bait technique on the one hand on released cohorts of reared, irradiated flies, and on the other hand on wild tsetse flies. In both cases, the footbath treatment was associated with a reduction of the apparent fly density probably related to an increased mortality. © 2006 Elsevier B.V. All rights reserved. (Resume d'auteur)

In Burkina Faso, Glossina palpalis gambiensis Vanderplank and G. tachinoides Westwood (Diptera: Glossinidae) are the main cyclic vectors of trypanosomiasis. The vegetation type along river banks is an important factor determining the distribution and abundance of these tsetse. The following work investigated the relation between the plant species present (including the disturbance level) and tsetse distribution and abundance, using three ecotypes, described by P.C. Morel in 1978. These were the Guinean, Sudano-Guinean and Sudanese gallery forests. In the Mouhoun River basin, these three ecotypes are found successively from upstream to downstream. Berlinia grandiflora, Syzygium guineense and Cola laurifolia and finally Acacia seyal and Mitragyna inermis were the best indicators for the Guinean, Sudano-Guinean and Sudanese gallery forest ecotypes, respectively, as suggested by Morel. However, other species such as Pterocarpus santalinoides and Mimosa pigra were not ecotype specific. Trap catches confirmed that G. palpalis and G. tachinoides are predominant in Guinean and Sudanese gallery forests, respectively, and that both species are well represented in the Sudano-Guinean ecotype. Tsetse densities dropped significantly in disturbed Sudano-Guinean and Sudanese gallery forest sites. However, this was not the case for both species in Guinean or for G. tachinoides in half-disturbed Sudanese gallery forest sites, confirming their high resilience to human-made changes. The importance of a detailed consideration of riverine ecotypes when predicting tsetse densities is discussed.

The classification of a Landsat Thematic Mapper satellite image helped demonstrate prevailing habitat types and land use intensity in the Volta basin of the Northern Region of Ghana. A geo-referenced data layer comprising the capture results of a cross-sectional survey of Glossina tachinoides Westwood was over-laid on a data layer of habitat types within 500 m of either bank of the Volta river and its tributaries. An evaluation of the relationship between habitat types and the capture results of G. tachinoides suggested a strong preference of G. tachinoides for woodland, followed by shrubland, grassland and flood plains. The findings were used to classify the suitability of habitat types for G. tachinoides as ‘high’, ‘medium’ and ‘low’ and a prediction map for the distribution of G. tachinoides in the entire river network was produced. The usefulness of this method in estimating the potential distribution of G. tachinoides in an area of increasing agricultural expansion is discussed.

The epidemiology of bovine trypanosomosis was investigated in two districts (Savelugu and West Mamprusi) of Northern Ghana with different land use and environmental characteristics. The land use intensity and environmental change was suspected to be higher in the Savelugu District. A cross-sectional entomological survey conducted along the White Volta river and its tributaries confirmed the presence of only Glossina palpalis gambiensis and G. tachinoides. The challenge index as measured by the product of tsetse density and tsetse infection rate was much higher in the West Mamprusi (19.6) than in the Savelugu district (4.7). A total of 1013 cattle (508 in Savelugu and 505 in West Mamprusi) were bled from a random selection of 16 villages in the Savelugu District and 13 villages in the West Mamprusi District. Blood samples were examined for trypanosomes by the buffy coat technique (BCT). Blood samples that were positive in the BCT or negative in the BCT but with packed cell volume (PCV) values below 21 were further tested with a polymerise chain reaction for trypanosomal DNA. Plasma samples of all cattle were serologically tested with an indirect ELISA for trypanosomal antibodies. The parasitological and serological prevalence of bovine trypanosomoses was significantly higher in West Mamprusi (16 and 53%, respectively) than in Savelugu District (8 and 24%, respectively). An evaluation of animal health at the village herd level, using PCV as an index of anaemia, provided various epidemiological scenarios prevalent in the entire study area. © 2004 Elsevier B.V. All rights reserved.

Dans les études de dynamique de population des glossines, vecteurs des trypanosomoses en Afrique, la taille de l'insecte peut être mise en relation avec leur longévité et leur capacité vectorielle. La taille des individus est généralement appréciée par la mesure de nervures remarquables de l'aile. Un logiciel semi-automatique a été développé par le Cirad et l'IRD pour réaliser une série de mesures à partir de photos numérisées des ailes. Il a été utilisé sur des populations sauvages de Glossina tachinoides Westwood et G. palpalis gambiensis Vanderplank (Diptera : Glossinidae) capturées autour de Bobo Dioulasso, au Burkina Faso. A partir d'une photo de l'aile, réalisée sous une loupe binoculaire et numérisée, le logiciel calcule la longueur des segments alaires, le rapport entre ces segments, la surface de la cellule "en hache" caractéristique des glossines et le niveau de gris de la membrane. Ces variables ont révélé leur intérêt taxonomique pour la diagnose entre ces espèces, mais également apportent des informations sur les caractéristiques physiologiques de la population étudiée.

Au Burkina Faso, les biotopes préférentiels des glossines ripicoles (Glossina tachinoides et Glossina palpalis gambiensis) ont été finement décrits dans le passé. Mais le milieu est actuellement soumis à une forte pression anthropique sous l'effet de "fronts pionniers" actifs (agriculteurs, agroéleveurs) entrainant des modifications des habitats naturels de ces glossines. Ce travail compare les résultats de deux enquêtes entomologiques réalisées de la même façon à 15 ans d'intervalle (1981-1996) sur plus de 120 krn de réseau hydrographique. La répartition géographique des insectes a évolué. Selon les situations, les densités de ces glossines ripicoles ont diminué, mais parfois augmenté. G. tachinoides s'adapte mieux que G. p. gambiensis à de fortes modifications de son habitat. Ces variations sont reliées aux changements dans l'occupation du sol, révélés par une étude diachronique d'images de télédétection à haute résolution (SPOT). Une forte relation entre la proximité des parcelles cultivées (< 300 m) par rapport à la galerie forestière et la densité des glossines est observée. L'implantation agricole se révèle dépendante de la géomorphologie (modelé et sol) en bordure des cours d'eau, qui constitue un indicateur du risque de dégradation des formations végétales riveraines et donc des densités de glossines. Ces résultats montrent la diversité des situations existantes, l'importance de l'échelle d'observation pour les études de répartition des vecteurs et l'intérêt de la physiographie comme indicateur d'utilisation des espaces riverains et par conséquent des situations entomologiques. Les pressions humaines ne se traduisent pas toujours par la régression des glossines ripicoles mais par un remodelage des faciès épidémiologiques.

En Afrique sub-saharienne, les trypanosomes restent des contraintes pathologiques majeures pour la santé humaine et pour le bétail. Dans le domaine vétérinaire, la lutte contre les vecteurs (Glossina tachinoides et G. palpalis gambiensis) repose sur les systèmes de piégeage. Pour être efficace, le piégeage doit être spatialement le plus ciblé possible. Les objectifs de ce projet sont d'identifier les zones d'interventions prioritaires, en mettant en évidence des indicateurs robustes de la présence des glossines, elle-même appréhendée à travers les activités anthropiques en vue de révéler à l'échelle du terroir les points épidémiologiquement les plus dangereux. Les informations recueillies sur une région géographique de 1300 Km2 montrent que les 2 espèces de glossines sont localisées dans les formations végétales le long des cours d'eau. La zone d'étude connaît une forte pression humaine liée à l'arrivée des agriculteurs. Cette évolution est parallèle à celle des populations des glossines. L'analyse PCR des glossines capturées montre d'importantes différences spatiales dans la combinaison vecteurs/parasites : dans les milieux occupés par l'homme, la majorité des glossines se nourrit sur les reptiles sauvages et porte rarement des parasites de bovins. Lorsque l'occupation humaine est importante, les mouches réalisent l'essentielle de leur repas sur les animaux domestiques, et hébergent en majorité des trypanosomes pathogènes pour le bétail

Les études récentes menées dans la zone de Sidéradougou (Burkina Faso) ont montré que les espèces ripicoles (Glossina tachinoides et G. palpalis gambiensis) sont présentes le long du réseau hydrographique principal. Cependant selon leur localisation, toutes ne sont pas infectées par les mêmes espèces de trypanosomes. Dans les zones peu anthropisées, les glossines se nourrissent essentiellement sur des reptiles et portent des parasites non pathogènes pour les bovins. Au contraire dans les sites régulièrement fréquentés par les animaux domestiques, la majorité des vecteurs s'alimente sur ces animaux et transmettent des trypanosomes pathogènes. Différentes situations épidémiologiques se côtoient ainsi à l'échelle de quelques kilomètres, et le risque de transmission dépend de l'intensité du contact entre les hôtes et les glossines plus que des densités d'insectes. Tous les facteurs environnementaux qui interviennent dans les interfaces entre les hôtes et les vecteurs ont été intégrés, grâce à l'utilisation d'un SIG, dans une approche globale qui associe l'entomologie, la parasitologie, l'écologie, l'occupation du sol et les différents systèmes d'élevage. Des outils de télédétection à haute résolution spatiale et des méthodes originales de modélisation ont été utilisés pour d'une part mettre en évidence les zones les plus favorables aux glossines le long du réseau hydrographique, et d'autre part décrire l'utilisation de l'espace par les éleveurs et les parcours quotidiens des animaux. Le croisement de ces informations permet de révéler les sites épidémiologiquement les plus dangereux, qui représentent finalement environ 10 % du réseau initialement prospecté.

A parasitological and entomological survey was conducted in the Sideradougou area (south of Bobo Dioulasso, Burkina Faso) in order to identify transmission factors of African trypanosomosis. A total of 3600 tsetse flies (Glossina tachinoides, Glossina palpalis gambiensis) were captured along 120 km of linear gallery forest and half of them were dissected. PCR analysis was undertaken on parasitologically positive flies (161 G. tachinoides, 92 G. palpalis gambiensis) to characterize the different trypanosomes. All the results were integrated in a GIS (Geographical Information System). Spatial repartition of the characterized trypanosomes enabled to recognize different areas with specific patterns of infection. Relations with environmental factors are discussed.

Une premiere etude sur l'evaluation de l'âge de Glossina tachinoides Westwood, 1850, par analyse des niveaux de gris de l'aile est realisee. Sur des lots de femelles provenant du laboratoire, cinq groupes apparaissent significativement differents. A condition d'etre validee sur des glossines naturelles, cette methode pourrait constituer une nouvelle approche de ce facteur important dans l'epidemiologie des trypanosomoses animales.. (Resume d'auteur)

La dynamique d'émission de T. congolense souche EATRO 325 (type savannah) est suivie quantitativement et qualitativement par examen microscopique du salivat et de la goutte anale récupérés tous les trois jours selon une méthode mise au point chez G. m. morsitans (mâles et femelles) et G. tachinoides (femelles). Chez ces deux glossines, l'apparition des trypanosomes a lieu à 3 jours dans la goutte anale et à 14 jours dans la salive. Le pourcentage moyen de glossines à salive positive sur la durée d'observation (60 jours) est identique chez les mâles et les femelles de G. m. morsitans (21,30 et 24,50 p. 100). Il est très supérieur à celui des G. tachinoides femelles (12,50 p. 100). Avec l'âge, le pourcentage de salivats positifs tend à s'accroître chez les femelles. L'association de l'examen des deux liquides offre la possibilité de suivre la dynamique d'installation et de maturation des trypanosomes à évolution cyclique chez l'insecte vivant.

Following a request from livestock owners, a campaign to eradicate tsetse flics was conducted in Dafinso (Burkina Faso) in 1993 and 1994. Traps impregnated with insecticide (Cypermethrin) were laid, and all livestock treated with deltamethrin. In February 1993 (before the campaign), the number of Giossina tachinoides (main species) trapped was 11.7/trap/day. In July 1993 (two months after laying the traps and the first treatment of cattle) the figure was zero. Entomological surveys throughout the period showed a rapid, lasting and almost total disappearance of the tsetse population. During 1994, no tsetse was caught. Livestock owners were actively and financially involved in the campaign from stars to finish. The present exemple shows the importance of cooperation from rural communities for successful and sustainable campaigns against trypanosomiasis

Lors d'experiences menees en 1992 et 1994 sur le site de la Comoe, par le Centre international de recherche-developpement sur l'elevage en zone subhumide (Bobo-Dioulasso, Burkina Faso), les auteurs ont compare l'efficacite des bouteilles et des cages associees aux pieges biconique Challier-Laveissiere ou monoconique Merot, comme systemes de capture pour certaines especes de glossines (Glossina tachinoides et G. morsitans submorsitans) et les Tabanidae. Pour G. tachinoides, la bouteille ne presente un net interet que lorsqu'elle est associee au piege monoconique, mais avec des resultats toujours inferieurs a ceux du piege biconique muni d'une cage. La bouteille avec le piege biconique donne des resultats variables selon les annees, mais au mieux equivalents a ceux de la cage. Les differences entre les systemes sont plus nettes chez les mâles. Pour G. morsitans submorsitans, le systeme piege biconique/cage reste le plus efficace et la bouteille reduit les captures dans les deux types de pieges. Les captures de Tabanidae sont augmentees (parfois doublees) quand on substitue la bouteille a la cage, quel que soit le type de piege. (Resume d'auteur)

Deux expériences sont menées en saison sèche au Burkina Faso sur le site expérimental de la Comoé (zone soudano-guinéenne), afin d'étudier l'influence de la position du sachet diffuseur de produits olfactifs pour Glossina tachinoides et Glossina morsitans submorsitans. Cet essai compare les positions interne et externe du méta-crésol et de l'association méta-crésol/octénol (proportions 3/1) dans des pièges biconiques. La position du sachet n'apparaît pas comme un facteur fondamental d'efficacité des pièges et les résultats obtenus sont variables selon la saison et l'espèce de glossine considérée. Des différences selon le sexe sont également notées. Le rôle de la distance n'a pas été étudié.

Cinq types de pièges sans produit olfactif sont comparés en saison sèche fraîche puis chaude le long de la rivière Comoé au Burkina Faso, pour leur efficacité vis-à-vis de Glossina tachinoides. Le piège biconique Challier-Laveissière donne les meilleurs résultats, alors que le piège monoconique Mérot et le piège F3 se révèlent très peu efficaces; le piège monoconique Vavoua et l'écran-piège fournissent des résultats intermédiaires. Les captures évoluent tout au long de la saison sèche au niveau quantitatif (augmentation du nombre total de glossines capturées) et au niveau qualitatif (prédominance des femelles pendant toute l'expérience, plus nette en deuxième période).

Cette note signale pour la première fois l'existence de chimiorécepteurs sur les ailes des mouches tsé-tsé. Ceux-ci sont principalement localisés sur le milieu de la nervure costale. Leur morphologie est comparable à celle des chimiorécepteurs observés sur les pattes. Leur nombre ne différe pas entre les sexes comme pour les pattes, mais entre les espèces. Ceci suggère un rôle dans la perception chimique proche de l'environnement, par rapport aux chimiorécepteurs des pattes qui semblent impliqués dans le comportement sexuel. L'étude a été conduite sur six espèces ou sous-espèces de glossines.

L'identication et le comptage des chimiorecepteurs ont ete etablis en microscopie classique et en microscopie electronique a balayage sur les pattes de Glossina tachinoides Westwood, 1850. Les auteurs presentent une carte de repartition des chimiorecepteurs, utile pour les recherches d'electrophysiologie et de comportement. Ces chimiorecepteurs localises sur le femur, le tibia et le tarse sont plus abondants sur les zones ventrales. Cette etude montre que les 3 paires de pattes possedent un nombre similaire de chimiorecepteurs et un important dimorphisme sexuel : 1033 chimiorecepteurs chez le mâle contre 570 chez la femelle. La variabilite du nombre de chimiorecepteurs pour les deux sexes a ete estimee sur la patte prothoracique (Resume d'auteur)

Au cours de la saison sèche 1980, les auteurs ont étudié la dispersion linéaire de deux glossines riveraines, G. p. gambiensis et G. tachinoides, le long de 35 km d'une galerie forestière bordant le cours supérieur de la Volta Noire, au Burkina-Faso. 35430 glossines ont été lâchées en tête de galerie après marquage, par fractions hebdomadaires, au cours de 3 séries d'expériences. L'analyse statistique fait appel aux tests non paramétriques appliqués à 3 indices spécialement retenus : un indice de "centralité" (médiane), un indice de longue distance (9e décile) et les distances maximales. Les longueurs parcourues augmentent significativement avec le temps pour les espèces et les sexes

The combination of a trapping system of insecticide impregnated screens and biconical traps followed by the release of sterile males led to the complete control of Glossina palpalis gambiensis and Glossina tachinoides in the agro-pastoral zone of Sideradougou. This area, situated south of Bobo Dioulasso, Upper Volta, in the Guinea savannah, covers an area of approx. 3000 km2. Along more than 650 km of rivers, bordered by gallery forests and infested by riverine tsetse, 6500 impregnated screens were placed during 4 months of the dry season, followed by the release of sterile males in the rainy season. For release purposes, colonies of 150,000 producing females of G.p. gambiensis and 85,000 females of G. tachinoides were maintained in industrial colonies on artificial membranes. Reinvasion of the project area was prevented by two barriers consisting of biconical traps impregnated with synthetic pyrethroid in one and simple biconical capture traps in the other. The screens reduced the initial fly population by 94% and permitted the release of only 35 sterile males per km of river to attain the planned ratio of seven sterile males to one wild male. Regular surveys showed that, after 4 months of release of sterile males, the relic fly population was constantly decreasing and tending towards disappearance. p ]An economic evaluation based on the production costs of the sterile males together with the costs of field operations showed that this combination of two non-pollutant methods was competitive with other methods of tsetse control.

Pour permettre le développement de l'élevage sur 240000 ha de la zone pastorale de Sidéradougou, le CRTA est intervenu sur 300000 ha. L'éli minatin de G. p. gambiensis et de G. tachinoides sur 600 km de gale ries forestières a reposé sur l'alternance de 2 méthodes non pollu antes utilisées en intégration : écrans insecticides et lâchers de mâles stériles. Après une phase préparatoire de 2 années (ouverture de pistes, prospection, barrières, etc.), le CRTA a mis en place 7204 écrans insecticides pendant la saison sèche 1983 suivis par les lâchers en saison des pluies, tous les 14 jours, à des points équi distants de 2 km sur le réseau hydrographique, de 379000 mâles irra diés. En 1984, 1/3 de la surface a été retraité avec des écrans, puis 467000 mâles irradiés ont été lâchés selon le même protocole. Le bon comportement des mâles irradiés et leur forte domination numé rique ont abouti à l'élimination des populations résiduelles, l'im pact de la lutte génétique étant suivi par l'examen des images ovaroutérines des femelles capturées. Les facteurs favorables et défavora bles au projet sont discutés, en particulier l'absence d'une législa tion pastorale devant l'afflux des troupeaux. Cette zone abrite ac tuellement entre 50000 et 70000 têtes de bétail.

Le CRTA de Bobo-Dioulasso a réalisé une campagne de lutte contre trois espèces de glossines (G. p. gambiensis, G. tachinoides et G. m. morsitans) dans une zone pastorale d'accueil de 3.500 km2 située à proximité de la ville. Les travaux se sont déroulés en deux phases : Une phase préparatoire de deux ans (1981-1982) a permis la création sur le terrain d'un réseau de 600 km de pistes, puis la prospection entomologique afin d'établir une carte de répartition des espèces de glossines présentes et de connaître leur densité apparente; La lutte proprement dite a également duré deux années (1983-1984). Deux méthodes ont été utilisées alternativement, selon la saison. La pose d'écrans insecticides en saison sèche a permis de faire baisser les populations de glossines d'environ 90 p. 100. Le lâcher de 850.000 mâles stérilisés par irradiation a été fait en saison des pluies. Cette zone, ainsi libérée des glossines par l'association de ces deux méthodes, et protégée des réinvasions par des barrières de pièges et d'écrans, est actuellement en plein aménagement.

Après avoir présenté quelques aspects de la physiologie de Glossina tachinoides Westwood, 1850, l'auteur expose les résultats de ses observations sur l'écologie de cette espèce, étudiée dans une zone marginale de son aire de répartition: la Réserve de Kalamaloué dans la vallée du bas-Chari. L'étude écologique envisage des relations de G. tachinoides avec le milieu environnant et aborde le problème de la dynamique de ses populations

La dynamique des populations de glossines constitue un aspect des plus importants, mais aussi des plus complexes de l'écologie de ces insectes. En raison des intérêts qu'elle présente: épidémiologique et pratique (liés à la mise au point de nouvelles méthodes de lutte, telles que l'introduction de mâles stériles par exemple), l'étude de la dynamique des populations de G. tachinoides a été abordée, par des méthodes classiques, à la Réserve de Kalamaloué. Elle a permis d'examiner les variations du sex-ratio, de la longévité et de la densité des glossines présentes, en toutes saisons, en différents gîtes de cette Réserve. Seules les recherches relatives aux adultes ont pu conduire à des résultats appréciables

Les auteurs ont étudié, pendant douze mois, l'étanchéité d'une barrière de 7 km, disposée tout au long d'une galerie forestière dense, étroite et continue, composée de 70 écrans ou pièges biconiques, imprégnés soit de D.D.T., de Deltaméthrine ou de Dieldrine, face à une pression constante exercée en aval par des glossines d'élevage (G. p. gambiensis: 86 102 et G. tachinoides: 9 536) lâchées de façon régulière et continue. Le contrôle de l'efficacité de ces barrières a été effectué à l'aide de 65 pièges biconiques de capture, disposés en amont du der-nier écran ou piège insecticide. Dans les conditions où ces observations ont été effectuées, il est apparu que seule la Deltaméthrine était capable d'assurer une étanchéité totale, même en saison des pluies, avec un avantage certain des pièges sur les écrans. Les causes de nature à expliquer la très faible efficacité du D.D.T. et de la Dieldrine sont discutées et les possibilités d'accroître la rémanence utile de la Deltaméthrine évoquées.

La larve libre a une vie brève. Elle s'immobilise et se transforme en pupe là où les conditions sont les plus favorables à la pupaison qui lui succède. Cependant l'action sur les pupes de facteurs externes, abiotiques (température, humidité) et biotiques (prédateurs, parasites, germes pathogènes), modifie la durée de pupaison et les taux d'éclosion. Dans les lieux de ponte, un équilibre de ces conditions favorables se maintient le plus souvent, mais il peut parfois être rompu, ce qui détermine alors une mortalité en pupes entraînant une diminution appréciable de la densité des populations adultes à venir