Life on the edge: tackling human African trypanosomiasis on the edge of wilderness areas

Boundary areas between different populations are the crucial places where pathogens spill over from one population to the other, and present a key risk for the emergence of new pathogens, or invasion by existing pathogens. An important example of this type of boundary are the edges of wilderness areas, where pathogens present naturally in wild animals can spill over to infect people and livestock living in the surrounding areas. In sub-Saharan Africa, this scenario often affects human populations with few economic resources. The proximity of vulnerable populations to areas harbouring pathogens provides a technical and moral challenge: how can biodiversity and economically productive wilderness areas be preserved without threatening the health and livelihoods of vulnerable people?

Our proposal will study the interaction between humans, livestock and wildlife and the role of this transition zone in the transmission of trypanosomes at the edge of the Serengeti National Park in Tanzania. These single-celled parasites are transmitted by the bite of tsetse flies. They do not cause any overt disease in wild animals within the Park, but humans bitten by tsetse infected with a particular species of trypanosome can develop sleeping sickness, a potentially fatal disease for which there is no preventative vaccine or drug. Other species of trypanosome also present in wild animals can cause a wasting, and ultimately fatal, disease in livestock.

Tsetse flies are highly mobile and can move from their natural habitat within the park to infect humans and livestock in surrounding areas. In east and southern Africa, the species of tsetse that transmit trypanosomes usually feed on wild animals rather than humans. However, changing housing and farming practices reduce the availability of wild hosts to tsetse and increase the risk of humans being bitten by infected flies. It is estimated that 12 million people in east and southern Africa are at risk of sleeping sickness and the preservation of wilderness areas present a chronic and intractable source of infection.
Preliminary data suggest however that there are restricted hotspots of disease risk, particularly at the edges of national parks, and that the application of modern methods of tsetse control to these hotspots will eliminate sleeping sickness foci.

To assess whether focussed control of tsetse is effective, we will develop mathematical models of the transmission of trypanosomes in the transition zone from wildlife-dominated areas on the park boundaries through to livestock-dominated areas outside the parks. The models will enable us to predict the likely extent, duration and cost of interventions required to interrupt the transmission of trypanosomes at boundary areas.

Parameter values for the models will be obtained using a combination of existing and new data on (i) the distribution, abundance, structure and infection status of tsetse populations, (ii) the densities of wildlife and livestock hosts, (iii) the number of livestock infected with trypanosomes, (iv) the composition and population genetics of the trypanosome populations and (v) the vegetational changes that occur at the boundary of the Serengeti National Park. The models will be validated by comparing the observed and predicted patterns of infection in the study area.

We will then use the models to predict the likely impact of various control interventions, and identify which are the most appropriate control measures for livestock keepers, NGOs and government agencies concerned with controlling trypanosomes at different distances from the boundaries of protected areas. The project's outputs will assist Tanzania and other countries affected by tsetse-borne trypanosomiases to develop cost-effective strategies for managing diseases at the transition zone between wildlife-protected and livestock-keeping areas.

The zoonotic form of Human African Trypanosomiasis (HAT) is caused by Trypanosoma brucei rhodesiense transmitted by tsetse flies. At the edge of wilderness areas, domestic cattle replace natural wild hosts (such as warthog and buffalo) as the principal reservoir host. We hypothesize that this shift towards a livestock-dominated system increases community reservoir potential and risk of human disease. Combining a wealth of ecological knowledge on the Serengeti ecosystem with new empirical data and models of HAT, we will quantify the transmission of trypanosomes across the ecotone between wilderness and settled areas and identify cost-effective strategies to interrupt transmission of HAT in the Serengeti and other wildeness areas of Africa.

To achieve this goal, we will:-

1: Develop novel models of the transmission of Rhodesian HAT which are spatially and temporally dynamic, thereby enabling us to model how the transmission of trypanosomes changes with the density, distribution and diversity of hosts and vectors.

2: Quantify the density, structure and feeding patterns of tsetse populations to test empirically the hypothesis that contact rates between host and vector species changes between wilderness and settled areas.

3: Identify and genotype trypanosomes from wild hosts, cattle and vectors to test empirically the hypothesis that the prevalence, population make-up and diversity of trypanosome populations changes across the ecotone and results in a greater risk of Rhodesian HAT.

4: Combine novel models (1) with empirical data (2,3) to identify 'ecologically smart' strategies to control human and animal trypanosomiasis in the Serengeti. The outputs will provide local, national and regional stakeholders with robust recommendations on cost-effective strategies to control human and animal trypanosomiasis in the wider Serengeti ecosystem and generate guidance on monitoring and managing Rhodesian HAT in wilderness areas.

Our project will lead to more effective control strategies for reducing human African trypanosomiases (HAT). The potential economic and societal impacts include:-

Reduced incidence of HAT
HAT is endemic in 171000 km2 of sub-Saharan Africa, imposing an annual health burden of 0.6M DALYs. A global programme to eliminate HAT by 2020 is based on active screening and case treatment. This approach is ineffective against Rhodesian HAT, the zoonotic form of the disease which threatens ~12M people, particularly those living in or near wilderness areas where reservoir hosts and tsetse are abundant. We will identify cost-effective strategies to improve control of Rhodesian HAT foci through tsetse or livestock focused interventions. The main beneficiaries will therefore be people living near wilderness areas.

Reduced burden of animal trypanosomiasis
The outputs from this project will also be used to improve efforts to control African Animal Trypanosomiasis which kills >1 million cattle a year across 35 countries of sub-Saharan Africa. Cheap and effective methods of tsetse control will also reduce the ~$35M spent annually by livestock keepers on trypanocides in Africa. Tanzania has the third largest livestock population in Africa, and a high proportion of poor livestock keepers; >4 million cattle are threatened by trypanosomiasis. Increasing animal productivity is likely to impact particularly on the rural poor, both in Tanzania and other affected countries.

Improved cost-effectiveness of strategies to control HAT in Tanzania and sub-Saharan Africa
In 2010-11, 48000 insecticide-treated targets were deployed to control tsetse in Tanzania, including 10000 specifically to control HAT in the Serengeti. Outputs from this project will ensure that these resources are deployed for maximum effect. Government, NGO, international (AU-PATTEC, WHO, FAO) and donor (DFID, BMGF) organizations concerned with controlling HAT will have more cost-effective options and decision support tools, provided via engagement workshops and online resources. The role of TTRI (project partners) as advisors to the Tanzanian Government on tsetse control, and our close links with the Ministry of Livestock Development and Fisheries, will ensure that project outputs reach policy makers to impact on future tsetse control plans. In particular, outputs from this project will contribute to the design and implementation of a programme to control trypanosomiasis over 15000 km2 of the Serengeti ecosystem being developed jointly by PATTEC and the governments of Kenya and Tanzania with support from BADEA.

Robust tourism industry
Tourism is a significant contributor to the Tanzanian economy and maintenance of wilderness areas as attractive and safe destinations is crucial. Even low numbers of HAT cases in tourists can have a significant impact on tourism. Preventing outbreaks of HAT is therefore important for both public and private sectors. This project will help to ensure that managers of protected areas have access to information on optimal tsetse control strategies.

Environmentally sensitive approaches
Tsetse and trypanosomiasis control can impact on non-target species and contribute to the development of drug and acaricide resistance. This project will promote strategies with negligible environmental impact, of particular importance in UNESCO World Heritage Sites such as Serengeti.

Improved capacity for trypanosomiasis research in Tanzania
The partnership of TTRI with world leading UK institutions will support the development of Tanzanian research in areas such as genetic analyses and mathematical modelling.

We will maximise this impact via three impact pathways:
1) Provide information to assist local decision making in the Serengeti area.
2) Contribute to a national trypanosomiasis control strategy for Tanzania.
3) Contribute to regional tsetse control initiatives.