Stage 1: Laying the Groundwork

The focus of Stage 1 is to develop technical capacities and to gain a sufficient understanding of AAT distribution, risk and impact for an evidence-based planning of field activities. The latter will be implemented in Stage 2 and beyond.

Capacity development

Essential capacities include project management, veterinary and entomological competencies in parasitological and serological surveillance, trapping and identification of vector species, and AAT and vector control. Skills in data management and geographic information systems (GIS) to enable mapping, risk assessment and monitoring are also needed ^{1, 2}.

Essential capacities must be built within the SNS, but more advanced ones (e.g. molecular diagnosis ³, geospatial modelling ⁴), can be available from national or regional centres and laboratories, as well as from international institutions.

Understanding AAT risk and impact

The establishment of a national-level information system is another pillar of Stage 1. All recent epidemiological and entomological data should be assembled, harmonized, geo-referenced and centralized. National atlases can be developed ¹, also using methodologies from the FAO continental Atlas of tsetse and AAT ^{5, 6}. Targeted field investigations should be conducted where gaps exist or where available information is too old to inform decision making. More generally, all necessary data for an evidence-based, rational selection of intervention areas and strategies need to be collected in Stage 1. In particular, if a fast-tracking to the elimination pathway is envisaged (Stage 3 and beyond), genetics studies are likely to be needed to establish the degree of isolation of the target tsetse populations ^{7, 8} and the related risk of reinvasion.

Socio-economic information on the burden of AAT is essential to justify investment and to prioritize areas for intervention. Spatially-explicit benefit-cost analyses ^{9, 10, 11}, tsetse and AAT distribution maps ^{1, 5, 6} and models of tsetse distribution and isolation ^{4, 12} are tools that should support a rational selection of intervention areas and strategies. The occurrence and risk of HAT ^{13, 15} should be considered, as interventions promoting One Health bring broader benefits and are more likely to attract resources ^{16, 18}. Security constraints (i.e. civil strife, armed conflicts, etc.) should not be overlooked.                

Pilot field interventions

While substantive field interventions are the focus of subsequent stages, pilot field activities against tsetse and AAT should be carried out in Stage 1. Their aim is to develop national capacities, fine-tune and optimize intervention tools, and motivate donors. Furthermore, throughout the PCP, field interventions may be needed to tackle possible AAT epidemics ¹⁹, including in Stage 1.

Steering committee

Stage 1 should also look at coordination. A steering committee should be set up, for orientation and supervision of the SNS and its activities. Membership should include national stakeholders (i.e., all concerned ministries such as livestock, agriculture, health, environment, etc.), as well as regional and international actors (e.g., regional economic communities (RECs), international organizations, and research institutions).

Selection of priority intervention areas and interventions strategies

Stage 1 culminates in the choice of priority intervention areas ²⁰ and most appropriate strategies for the selected areas (AAT sustainable reduction or elimination). Importantly, the most likely strategy for subsequent stages can, to some extent, influence activities in Stage 1. For example, requirements in terms of data and capacities differ between the sustainable reduction and elimination scenarios, and this could affect activities and duration of Stage 1.T.

References

¹ Ahmed, S.K. et al., An atlas of tsetse and bovine trypanosomosis in Sudan. Parasit. Vectors. 2016; 9: 194

² Cecchi, G. and Mattioli, R., Geospatial Datasets and Analyses for an Environmental Approach to African Trypanosomiasis.

³ Seck, M. et al., The prevalence of African animal trypanosomoses and tsetse presence in Western Senegal. Parasite. 2010; 17: 257–265

⁴ Dicko, A.H. et al., Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal. Proc. Natl. Acad. Sci. U.S.A. 2014; 111: 10149–10154

⁵ Cecchi, G. et al., Developing a continental atlas of the distribution and trypanosomal infection of tsetse flies (Glossina species). Parasit. Vectors. 2015; 8: 284

₆ Cecchi, G. et al., Assembling a geospatial database of tsetse-transmitted animal trypanosomosis for Africa. Parasit. Vectors. 2014; 7: 39

⁷ Solano, P. et al., Population genetics as a tool to select tsetse control strategies: suppression or eradication of Glossina palpalis gambiensis in the Niayes of Senegal. PLoS Negl. Trop. Dis. 2010; 4: e692

⁸ Adam, Y. et al., Genetic comparison of Glossina tachinoides populations in three river basins of the Upper West Region of Ghana and implications for tsetse control. Infect. Genet. Evol. 2014; 28: 588–595

⁹ Shaw, A. et al., Mapping the economic benefits to livestock keepers of intervening against bovine trypanosomosis in Eastern Africa. Prev. Vet. Med. 2014; 113: 197–210

¹⁰ Shaw, A. et al., Mapping the benefit–cost ratios of interventions against bovine trypanosomosis in Eastern Africa. Prev. Vet. Med. 2015; 122: 406–416

¹¹ Shaw, A.P. et al., Estimating the costs of tsetse control options: an example for Uganda. Prev. Vet. Med. 2013; 110: 290–303

¹² Bouyer, J. et al., Mapping landscape friction to locate isolated tsetse populations that are candidates for elimination. Proc. Natl. Acad. Sci. U.S.A. 2015; 112: 14575–14580

¹³ Simarro, P.P. et al., The Atlas of human African trypanosomiasis: a contribution to global mapping of neglected tropical diseases. Int. J. Health Geogr. 2010; 9: 57

¹⁴ Simarro, P.P. et al., Estimating and mapping the population at risk of sleeping sickness. PLoS Negl. Trop. Dis. 2012; 6: e1859

¹⁵ Simarro, P.P. et al., Monitoring the progress towards the elimination of gambiense human African trypanosomiasis. PLoS Negl. Trop. Dis. 2015; 9: e0003785

¹⁶ WHO. Control and Surveillance of Human African Trypanosomiasis. 2013

¹⁷ Simarro, P.P. et al., Monitoring the progress towards the elimination of gambiense human African trypanosomiasis. PLoS Negl. Trop. Dis. 2015; 9: e0003785

¹⁸ Grant, C. et al., Stakeholder narratives on trypanosomiasis, their effect on policy and the scope for One Health. PLoS Negl. Trop. Dis. 2015; 9: e0004241

¹⁹ Van den Bossche, P. and Delespaux, V., Options for the control of tsetse-transmitted livestock trypanosomosis. An epidemiological perspective. Vet. Parasitol., 181 (2011), pp. 37-42

²⁰ Mattioli, R. et al., Tsetse and trypanosomiasis intervention policies supporting sustainable animal-agricultural development. J. Food Agr. Environ., 2 (2004), pp. 310-314.

Stage 2: Sustainable AAT Reduction

The focus of Stage 2 is a sustainable and economically-profitable reduction in AAT risk and burden by creating areas of low AAT incidence and impact, whereby only sporadic treatments with trypanocides are needed and the risk of emergence and/or spread of drug resistance is minimized ^{1, 2}.

The intervention strategy hinges on the integrated management of AAT ^{2, 3}, a community/farmer based approach that relies on the collaboration of local veterinary services and farmers associations, taking into account eco-epidemiological settings, livestock production systems ⁴, and cattle breeds. Effective strategies will require the combined use of tsetse control methods, diagnostic tests and trypanocidal drugs. Improved nutrition and the control of other parasitic diseases would also be beneficial ^{5, 6}.

Baseline and monitoring data, including parasitological, entomological, and socio-economic data, need to be collected in the intervention areas to guide field activities, fine-tune intervention strategies and measure progress and impact. The possible presence of drug resistance should be considered, and if necessary investigated.

Regarding capacity development, all actors involved in the integrated AAT management should be targeted, including livestock keepers and farming communities at large, public and private veterinary services, as well as the SNS. Emphasis should go on the correct use of trypanocides to limit the emergence and spread of drug resistance ¹ and on efficient and cost-effective vector control techniques, particularly insecticide treated cattle (ITC) ^{7, 8}, livestock protective fences (LPF) in the case of zero-grazing rearing systems ⁹ and insecticide treated targets (ITT), especially where tsetse pressure from protected areas has to be prevented ¹⁰.

The main challenge in Stage 2 is sustainability, which will have to rely on the sensitization and training of veterinary services, farmer associations and individual farmers. Funding mechanisms must be put in place to ensure that interventions are sustained with minimal support from extension services ¹¹. The latter should focus on maintaining awareness and securing the availability and appropriate use of affordable, efficient and cost-effective control tools ¹². Importantly, farmer communities must be fully involved in the devolvement of the integrated disease management strategies to ensure that they are adapted to the target livestock-agricultural production systems and more generally to local constraints. Adoption of new technologies, such as tiny targets, LPF, restricted application of insecticide on animals and repellent–insecticide associations, normally requires external support, a good knowledge of local socio-technical networks, a strong participatory approach and co-learning processes to adjust the techniques to the users ¹³. The degree of adoption of the proposed strategy by stakeholders will depend on their appreciation of the benefits and risks derived from the intervention activities and the associated changes required within their farming system ¹⁴.

Stage 2 could be sustained indefinitely, with AAT management becoming a fixed production cost ¹⁵. However, the strategy should be reassessed at regular intervals (three to five years). Should the epidemiological and socio-economic conditions become favourable, a shift towards an elimination strategy (Stage 3) can be envisaged. 

References

¹ Giordani, F. et al., The animal trypanosomiases and their chemotherapy: a review. Parasitology (2016), pp. 1-28

² Van den Bossche, P. and Delespaux, V.,  Options for the control of tsetse-transmitted livestock trypanosomosis. An epidemiological perspective. Vet. Parasitol., 181 (2011), pp. 37-42

³ Bouyer, J. et al., ​Community- and farmer-based management of animal African trypanosomosis in cattle. Trends Parasitol., 29 (2013), pp. 519-522

⁴ Cecchi, G. et al., ​Geographic distribution and environmental characterization of livestock production systems in Eastern Africa. Agric. Ecosyst. Env., 135 (2010), pp. 98-110    

⁵ Mungube, E.O. et al., Best-bet integrated strategies for containing drug-resistant trypanosomes in cattle. Parasit. Vectors, 5 (2012), p. 164

⁶ Katunguka-Rwakishaya, E. et al., The influence of supplementation with cotton seed cake on the resistance of Ugandan goats to primary and secondary challenges with Trypanosoma congolense and on their response to treatment. Vet. Parasitol., 70 (1997), pp. 67-76

⁷ Bouyer, J. et al., Control of bovine trypanosomosis by restricted application of insecticides to cattle using footbaths. Vet. Parasitol., 161 (2009), pp. 187-193

⁸ Torr, S.J. et al., Less is more: restricted application of insecticide to cattle to improve the cost and efficacy of tsetse control. Med. Vet. Entomol., 21 (2007), pp. 53-64

⁹ Bauer, B. et al., Managing tsetse transmitted trypanosomosis by insecticide treated nets—an affordable and sustainable method for resource poor pig farmers in Ghana. PLoS Negl. Trop. Dis., 5 (2011), e1343  

¹⁰ Van den Bossche, P., A changing environment and the epidemiology of tsetse-transmitted livestock trypanosomiasis. Trends Parasitol. 26 (2010), 236-243  

¹¹ Catley, A. and Leyland, T., Community participation and the delivery of veterinary services in Africa. Prev. Vet. Med., 49 (2001), pp. 95-113

¹² Sutcliffe, O.B. et al., Animal trypanosomosis: making quality control of trypanocidal drugs possible. Rev. Sci. Tech. OIE, 33 (2014), pp. 813-830

¹³ Bouyer, J. et al., Community- and farmer-based management of animal African trypanosomosis in cattle. Trends Parasitol., 29 (2013), 519-522

¹⁴ Bouyer, J. et al., Restricted application of insecticides: a promising tsetse control technique, but what do the farmers think of it? Vet. Parasitol., 161 (2009), 187-193

¹⁵ Shaw, A. et al., Mapping the benefit–cost ratios of interventions against bovine trypanosomosis in Eastern Africa. Prev. Vet. Med., 122 (2015), pp. 406-416

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).

References

¹ Bouyer, J. et al., Stratified entomological sampling in preparation for an area-wide integrated pest management program: the example of Glossina palpalis gambiensis (Diptera: Glossinidae) in the Niayes of Senegal. J. Med. Entomol., 47 (2010), pp. 543-552

² Percoma, L. et al., Enquêtes entomologiques préparatoires à une lutte à grande échelle contre les glossines, assistées par un système d’information géographique: cas de la Pattec au Burkina Faso. Rev. Elev. Med. Vet. Pays Trop., 68 (2016), pp. 157-165

³ Dicko, A.H. et al., Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal.

⁴ Vreysen, M.J et al., Tsetse flies: their biology and control using area-wide integrated pest management approaches. J. Invertebr. Pathol. 112 (2013), S15-S25

⁵ Seck, M. et al., The prevalence of African animal trypanosomoses and tsetse presence in Western Senegal. Parasite, 17 (2010), pp. 257-265

⁶ Adam., Y. et al., Bovine trypanosomosis in the Upper West Region of Ghana: entomological, parasitological, and serological cross-sectional surveys. Res. Vet. Sci., 92 (2012), pp. 462-468

⁷ Sow, A. et al.. Baseline survey of animal trypanosomosis in the region of the Boucle du Mouhoun, Burkina Faso. Res. Vet. Sci., 94 (2013), pp. 573-578

⁸ Bouyer, F. et al., Ex-ante benefit-cost analysis of the elimination of a Glossina palpalis gambiensis population in the Niayes of Senegal. PLoS Negl. Trop. Dis., 8 (2014), p. e3112

₉ Shaw., A. et al., Mapping the benefit–cost ratios of interventions against bovine trypanosomosis in Eastern Africa. Prev. Vet. Med., 122 (2015), pp. 406-416

¹⁰ Kgori, P.M. et al., The use of aerial spraying to eliminate tsetse from the Okavango Delta of Botswana. Acta Trop., 99 (2006), pp. 184-199

¹¹ Vreysen, M.J. et al., Sterile insects to enhance agricultural development: the case of sustainable tsetse eradication on Unguja Island, Zanzibar, using an area-wide integrated pest management approach. PLoS Negl. Trop. Dis., 8 (2014), p. e2857.

₁₂ Vreysen, M.J. et al., Glossina austeni (Diptera: Glossinidae) eradicated on the island of Unguja, Zanzibar, using the sterile insect technique. J. Econ. Entomol., 93 (2000), pp. 123-135

¹³ Bouyer, J. et al., Trypanosomosis: control methods. P.-C. Lefèvre (Ed.), Infectious and Parasitic Diseases of Livestock, Éditions Lavoisier (Tec & Doc) (2010), pp. 1936-1943

Stage 4-5: eliminating AAT

The focus of Stage 4 is the elimination of AAT transmission and the establishment of AAT-free areas. In Stage 4 the maintenance of some of the control measures deployed in Stage 3 is still required. In Stage 5 all control measures are lifted, and the free-status should be maintained in their absence.

A monitoring system including sentinel herds to assess AAT incidence is required, to ensure the absence of circulation of parasites and the absence of tsetse (when tsetse elimination was targeted in Stage 3). Serological tests for the detection of antibodies against trypanosomes ¹ or tsetse saliva antigens ² could be useful to demonstrate the absence of parasite circulation or the absence of tsetse.

References

¹ OIE (2013) Trypanosomosis (Tsetse-transmitted). In Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, World Organisation for Animal Health, OIE (2013)

² Somda, M.B., et al., Identification of a Tsal152-75 salivary synthetic peptide to monitor cattle exposure to tsetse flies. Parasit. Vectors, 9 (2016), p. 149