Progress towards the eradication of Tsetse from the Loos islands, Guinea

Abstract

Background: The tsetse fly Glossina palpalis gambiensis is the main vector of sleeping sickness (Human African Trypanosomiasis - HAT) in West Africa, in particular in littoral Guinea where this disease is currently very active. The Loos islands constitute a small archipelago some 5 km from mainland Guinea, where G. p. gambiensis is well known as a nuisance and potential disease vector by inhabitants of the three main islands, Fotoba, Room, and Kassa. The National Control Program against HAT of Guinea has decided to eradicate tsetse in Loos islands in order to sustainably protect humans and economic activities. After baseline data collection, tsetse control began on the islands in 2006. On each of the three islands a specific combination of control methods was implemented according to the entomological situation found.

Results: Starting densities before control operations were 10, 3 and 1 tsetse/trap/day in Kassa, Room and Fotoba respectively, but by July 2010, tsetse were no longer caught in any of the sentinel traps used for monitoring. The reduction rate was faster where several control methods were implemented as a combination (impregnated traps and targets ITT, selective groundspraying, epicutaneous insecticide treatment of pigs, and impregnated fences around pig pens), whereas it was slower when ITT were used as the only control method.

Conclusions: This 100% suppression is a promising step in the eradication process, but G. p. gambiensis may still occur at very low, undetectable, densities on the archipelago. Next step will consist in assessing a 0.05 probability of tsetse absence to ascertain a provisional eradication status. Throughout these operations, a key factor has been the involvement of local teams and local communities without whom such results would be impossible to obtain. Work will continue thanks to the partners involved until total eradication of the tsetse on Loos islands can be declared.

Figure 1

Pictures illustrating the different control techniques used against G. palpalis gambiensis on Kassa island, Guinea. From upper left to lower right are shown epicutaneous treatment using insecticide (pour on) on pigs, deltamethrin impregnated fences around pig pens, a deltamethrin impregnated black/blue/black target in a palm tree plantation, and cyfluthrin groundspraying using a Swinfog SN50.

Figure 2

Combination and GPS location of control techniques applied on Loos islands. This map shows exact GPS locations of places where the different control techniques (see legend) were implemented on each of the three islands, together with the location of monitoring traps.

Figure 3

Overall evolution of G. p gambiensis densities according to the different control operations applied on the three islands. The graph shows the evolution of tsetse densities ([log (count+1)], Y axis) on the three islands according to each monitoring surveys (circles) (X axis showing year and months). Under the graph are detailed the different control methods implemented on each island and the date when they were implemented.