Our systematic review of the available published and unpublished data provided a synoptic picture of the distribution of tsetse fly and AAT in Burkina Faso for the period 1990–2019. The atlas updates the latest national tsetse distribution map produced in 1977 [37], whose northern limit had been updated in 2010 [32]. Detailed distribution maps of the four tsetse species present in Burkina Faso are also presented. As far as AAT is concerned, the distribution maps presented in this paper, based on the testing of over 50,000 animals, are the first of their kind in Burkina Faso.
However, as observed in similar national mapping exercises [19–21, 18, 22], a number of gaps not attributable to the data compilation and processing still affect our knowledge of the distribution of tsetse fly and AAT in Burkina Faso. The gaps are related to the inherent limitations of the existing datasets, and in particular to the geographical coverage, range of animal species tested and diagnostic methods.
With regard to the geographical coverage, the main gap in the atlas is the severe lack of information from the north, north-east, north-west, centre and extreme east of the country. This situation is explained by the fact that institutions involved in tsetse and AAT research and control in Burkina Faso focus their investigations and efforts on the regions of highest tsetse infestation [14], [38]). As already observed in Mali [20], this lack of information on a large part of the national territory hides the true extent of the AAT problem in the country.
As regards the animal species tested for AAT, more than 90% of atlas data are on cattle. However, in Burkina Faso small ruminants (i.e. sheep and goats) far exceed cattle in terms of population numbers. Furthermore, the diagnostic technique used to test blood samples was the BCT technique for more than 60% of the samples. While parasitological techniques based on blood concentration may be appropriate for treatment decisions [39], they are known to have low sensitivity and to underestimate the true prevalence of the disease [36].
Despite the limitations, the atlas provides a fairly accurate assessment of the geographic distribution of three tsetse species of veterinary importance in Burkina Faso: Glossina palpalis gambiensis, Glossina tachinoides, and Glossina morsitans submorsitans. Glossina. medicorum, because of its limited distribution, has a very low impact on AAT transmission in Burkina. A fifth species, G. longipalpis, had been reported in Burkina Faso, in particular in the South West Region in the zone of Batié [37]. However, the last observation was in 1961 [37], while recent data from this region are insufficient to rule out its possible persistence.
Thanks to their adaptation capacity to land cover changes and vegetation degradation, tsetse species of the riverine group (i.e. palpalis) are confirmed to be the most widespread in Burkina Faso [37]. In particular, the geographical range of G. tachinoides extends from the East to the West of the country, and the species is now found also in some previously free areas (e.g. western part of the Orodara Department) [37].
As regards savannah species, their distribution is fragmented and confined to a few protected areas. This patterns has been observed in other countries in western Africa [18], as a result of habitat degradation, land cover changes and the depletion of the wild fauna, their preferred hosts [40]. Glossina morsitans submorsitans is found along the southern border between Burkina Faso and Ghana and Benin, as well as in the pastoral zones in the western part of the country (Samorogouan and Sideradougou). Glossina medicorum was reported from one province in the south-western part of the country (Comoé), while it had been previously reported also along of the borders with Ghana, Togo and Benin [37].
Overall, our study seems to corroborate the notion that in recent years the distribution of tsetse species in Burkina Faso has been affected by droughts and demographic pressure [41].
Regarding animal trypanosomosis, the three major trypanosome species infective for livestock (T. vivax, T. congolense and T. brucei) are widespread in the country. Serologically positive animals, not confirmed parasitologically, have been reported also from the north of the country (Djibo Department) [33]. The absence of parasitological confirmations in these areas is ascribed to the combined effect of the absence of cyclical vectors and the trypanocidal drug treatments administered by livestock keepers before, during and after transhumance in the AAT enzootic area [33]. In this context, it is unclear whether any of the serological positive animals identified in the North area have been infected locally.
In Burkina Faso, T. vivax is the most widespread trypanosome species follow by T. congolense. This could be related to the ability of T. vivax to be mechanically transmitted by Stomoxys and Tabanids [42]. Mechanically transmitted of T. congolense is also well-know [42]. These parasites are also transmitted mechanically by tsetse flies [43, 42] and especially by many other haematophagous insects [44, 42]. In some contexts, these mechanical transmissions act as an amplifying factor for the disease [45–47]
T. brucei has been found confined in protected areas of the country, in the west, south-west and Centre-east. These infested areas are economic interest to the country, including pastoral areas, a park and a reserve. These areas would be inhabited by wild or domestic animals that are reservoirs of the disease.
The highest serological prevalence show in this study indicates that many animals have been in contact with the trypanosomes even from animals of tsetse free area.
The AAT prevalence obtained in this study may be underestimated because of that most of the diagnosis methods used was by BCT.