Stage 3: initiating AAT elimination
The focus of the PCP’s final stages (3 to 5) is to create sustainable AAT-free areas. In particular, the focus of Stage 3 is the interruption of AAT transmission. Many activities already described for Stage 2 have to be carried out (or continued) in Stage 3, but emphasis differs. The collection of baseline and monitoring data is more intensive than in Stage 2, so as to address the higher information requirements of an elimination campaign [1, 2]. Focus is on tsetse data, including longitudinal monitoring of tsetse densities [3], age structure and natural abortion rates (the latter only needed to measure SIT-induced abortion rates, if a SIT component is planned) [4]. At very low tsetse densities, advanced statistical analysis of tsetse catches is needed to measure the probability of having achieved tsetse elimination [3]. Despite the emphasis on tsetse data, essential AAT [5-7] and socio-economic data [8] are still needed.
In order to eliminate tsetse flies in the target area, a suppression phase focuses on the reduction of tsetse densities, while a second mop-up phase completes the elimination. A range of tools can be used in the process, either alone but preferably in combination following an integrated pest management approach. These include the methods already mentioned in Stage 2 such as ITC and ITT. However, more expensive methods can be used in an elimination context [9], like SAT [10] and SIT [11, 12]. Some of the methods are more appropriate for suppression, while others are more effective for elimination. For example, SIT is the only technique with inverse density dependent efficiency (i.e. it works best when wild tsetse densities are very low), so it is particularly efficient for elimination [13].
Once tsetse flies are eliminated, the need to clear the parasite reservoir in livestock should be evaluated. A blanket treatment may be particularly important to eliminate T. vivax, whose mechanical transmission can occur in the absence of tsetse. Control and surveillance of livestock movement may also be necessary to reduce the risk of disease reintroduction.
Compared with Stage 2, AAT elimination requires more centralized, top-down management and coordination. Despite this, farmers’ sensitization and involvement remains crucial. Public information campaigns (e.g. radio, TV, etc.) ensure the engagement and support of the beneficiaries, who can also contribute directly to the campaign (e.g. if ITC is used).
Transition from Stage 3 to Stage 4 is linked to the interruption of AAT transmission (i.e. not directly to the elimination of the tsetse vector).