Int. J. Environ. Res. Public Health 2010, 7 1715 The present study should be extended to other countries of West Africa, in particular those for which a national tsetse control campaign is planned. The existence of models attempting to predict areas of tsetse suitability [21] is helpful; however, for operational control updating tsetse presence in the field is undoubtedly mandatory since substantial differences can occur between the predicted tsetse presence and the actual distribution, as observed in Burkina Faso by [22] and in the present study (data not shown). What will be of key interest to tsetse control planning as a next step could be modeling what has been observed here to predict the future evolution of tsetse and trypanosomiasis, taking into account the climatic scenario [41,42] and projections of human growth [43]. 3. Experimental Section Entomological data were recorded from previously reported northern tsetse limits in Burkina Faso. Some were from observations made at the beginning of the last century (Missions Bouët-Roubaud 1906–1916 and Jamot 1933–1935), from which a map was drawn up in 1935 [25]. Later, following other entomological surveys conducted by the SGHMP between 1944 and 1949, another map was prepared in 1949 [26]. Then in 1977, Office de Recherche Scientifique et Technique d’Outre-Mer (ORSTOM) scientists updated these observations [23]. More recently, all entomological data recorded in the last 10 years come from different research projects based at CIRDES Bobo-Dioulasso, the National Livestock Laboratory (LNE) and the Burkina Faso national PATTEC project (PCZLD: Projet de Création de Zones Libérées Durablement de la tsé- tsé). The methodology used by PATTEC-PCZLD is fully described in [44]. Present surveys conducted by CIRDES/LNE also used biconical traps [45] to catch tsetse along the main rivers and their tributaries. Traps were left for three consecutive days, with cages harvested daily. Tsetse were then identified according to species and sex, and counted. Tsetse were noted absent if there were no tsetse caught in the trap over these three consecutive days. Rainfall data between 1931 and 1970 and between 1961 and 1989 were recorded by the Institut Géographique du Burkina Faso (IGB) and of the Burkina Faso meteorology department. Information on human settlements was recorded from [35] and recent data on settlements were recorded by [36]. 4. Conclusions Updating the tsetse northern distribution limit in Burkina Faso and comparing maps made in the beginning of 20th century to the current ones have demonstrated a north-to-south shift of this limit. The maximum shift toward the south since 1949 is around 200 km, and the tsetse belt in Burkina Faso has decreased by around 70,000 km2 (one-quarter of the country). Concurrently, the density of several tsetse species has decreased and some of them have almost disappeared, such as G. morsitans submorsitans, which only remains present in protected areas (national parks, wildlife areas). The Burkina Faso tsetse belt has now become discontinuous since it is now made up of two belts, one western and one eastern. The first use of these observations is operational since it allows the PATTEC national project to target areas for tsetse control in programs begun on the Mouhoun basin in November 2009. Two factors seem to have played a major role in this quantitative and qualitative evolution. The severe drought episodes locally modified key factors for tsetse such as vegetation, shade, hygrometry,