Int. J. Environ. Res. Public Health 2010, 7 1711 be seen from 1916 to 1949, and then from 1949 to 1977, the northern tsetse fly limit has shifted north to south but this shift has varied depending on the longitude. Figure 1. Northern tsetse limit in Burkina Faso from 1906 to 2009. 2.2. Current Northern Tsetse Limit in Burkina Faso The updated limits of the most northern points in which tsetse were found present or absent in traps were added to these previously recorded limits, comprising the northern points at which (Figure 1). In the western part of the country (Mouhoun basin), G. palpalis gambiensis was caught as well as G. tachinoides and G. morsitans submorsitans. In the central part of the country (Ouagadougou region), only G. tachinoides was caught. In the eastern region of Burkina Faso (Po, Pama, Arly), G. morsitans submorsitans was present with G. tachinoides, especially in the protected areas (national parks, game reserves), but also in the savannahs. Hence, in the Mouhoun basin it appears that G. palpalis occurs mainly upstream (up to the Mouhoun loop north of the Mouhoun River), while G. tachinoides were caught downstream. Both species co-occur in the intermediary area east of the Mouhoun river basin, except in the protected areas where G. morsitans submorsitans were caught, all the collected flies were only G. tachinoides. According to the results of the present surveys, the northwestern tsetse limit starts at the same latitude as the Challier and Laveissière 1977 limit up to the Mouhoun loop, where the limit then proceeds south following the Mouhoun River. Therefore, the limit around Koudougou is now