Int. J. Environ. Res. Public Health 2010, 7 1712 around 12°25′N, and then crosses South Ouagadougou before shifting north again along the Nakambe River (previously known as the Red Volta). At the Nakambe longitude (1°W), the limit shifts right to the south toward Tenkodogo (11°65N) before disappearing at the Togo border (11°N) in this region. This means that here the northern tsetse limit is no longer in Burkina Faso but found in Togo, over a distance of 100 km. This is important when attempting to control tsetse since it means that there are now two separate tsetse belts in Burkina Faso. Tsetse (G. morsitans submorsitans and G. tachinoides) appear again in Burkina Faso at the Pama longitude (0.80°E) around the Kompienga River and surround the Pama protected areas (Arli). The limit then turns up along the Pendjari River, up to the W game park to the Niger border (12°4′N). Therefore, the most northern point (12°76′N; 03°43′W) at which tsetse have been caught in Burkina Faso is located just north of the Mouhoun loop, in the western part of the country. The most northern points on the other two main rivers are 12°31′N for the Nazinon River and 12°44′N on the Nakambe River. This update of the northern tsetse limit distribution in Burkina Faso shows that there has been a variable north–south shift of this limit depending on the longitudes. This shift appears to be consistently directed from north to south, never the opposite at this scale. This shift is minimal in the western part of the country, but quite considerable in the east. It can be approximated as a mean of ~100 km to the south, but is variable according to numerous specific local situations. From 1949 to 2009, the tsetse belt in Burkina Faso lost approximately 70,000 km2 (one-quarter of the land surface area in Burkina Faso) due to the combination of a decrease in rainfall and an increase in human density. The largest shift is located in a quadrilateral included within the Tougan-Koudougou- Ouagadougou-Kaya perimeter (the historical focus of SS in Burkina Faso during the 1930s) where tsetse are no longer found today. This is quite impressive when recalling the words of Dr. Gouzien in 1908, who wrote: “Les glossines existent dans la vallée du Niger de Tombouctou à Gaya, dans les marigots de la Boucle, dans la région de Dori, le long de la Sirba et du Yali et aussi en abondance sur les bords du Tchad” [24] - meaning that in a century, tsetse have lost around 500 km of their northern distribution (from the Niger River at Tombouctou to the Mouhoun loop at Dédougou), and are now discontinuously distributed since there are two separate tsetse belts. It should be noted that, despite rigorous care in the design and implementation of our surveys, it may still be possible that errors have been made in the picture of the tsetse’s northern limit (as is also possible in former surveys). The presence of flies is always much easier to record than their absence (see [27]). However, the aim of this study was to draw a general trend of tsetse distribution in Burkina Faso. Consequently, it cannot be entirely ruled out that isolated populations located north of the proposed limit have been missed, and there may be areas without tsetse below the limit. 2.3. Impact of Global Change on Tsetse Distribution The West Africa sub-region experienced several drought episodes during the 19th and 20th centuries, which provoked successive famines in the Niger loop [28]. During these droughts, not only rainfall and temperature changed [29], but river flows were also modified [30], which consequently orientated people to the south and along rivers for water, agriculture and livestock tending. In Burkina Faso, three main drought episodes were identified by [31]: 1940–1949, 1970–1979, 1980–1989. Actually, previous entomological data by [23] and [24] were collected during or after these episodes.