ENABLES: Enabling Livestock-keepers to Eliminate Sleeping Sickness

Edges of wilderness areas, where pathogens occurring naturally in wild animals can spill over to infect people and livestock in surrounding areas, are a key risk for the emergence of new pathogens and spread of existing ones. In sub-Saharan Africa, this scenario often affects poor and marginalised human populations. The proximity of vulnerable populations to these areas provides a technical and ethical challenge: how can biodiversity and economically productive wilderness areas be preserved without threatening the health and livelihoods of vulnerable people?

ENABLES builds on our work at the edge of the Serengeti National Park in Tanzania where tsetse flies transmit trypanosomes. These single-celled parasites do not cause any overt disease in wild animals, but do cause a disease called Nagana in livestock. Humans bitten by tsetse infected with a particular species of trypanosome can develop sleeping sickness (Rhodesian human African trypanosomiasis, r-HAT), an acute and fatal disease for which there is no preventative vaccine or drug. About 12 million people in east and southern Africa are at risk of r-HAT and the preservation of wilderness areas presents a chronic and intractable source of infection. Only Botswana has been able to solve the problem of r-HAT permanently by eradicating tsetse from the Okavango wilderness area through large-scale (~15,000 km2) aerial spraying. This complex and expensive solution is not feasible for most poor communities living on the edge of wilderness areas.

Our work in Serengeti suggests that livestock-keepers are preventing the spread of r-HAT by simply applying pyrethroid insecticides to their cattle. They do this to control the ticks and tsetse that carry livestock diseases (East Coast Fever, Nagana) but this cheap (~$6/animal/year) and easy method also interrupts transmission of r-HAT. By treating livestock to prevent animal diseases, livestock-keepers are protecting local people from r-HAT. Other countries have tried but failed to encourage widespread use of pyrethroids by livestock-keepers as part of a One Health approach against r-HAT. Uptake in Tanzania appears to be stimulated, at least in part, by a government subsidy on the price of pyrethroids.

While our discoveries in Serengeti offer the exciting prospect of a One Health solution to r-HAT, we do not know (i) how widespread pyrethroid use is in different livestock systems, (ii) how generally applicable this approach is, and (iii) what conditions make farmer-led control likely and effective.

ENABLES will test the hypothesis that national policies to promote use of pyrethroids by livestock-keepers have led to large-scale control of human and animal trypanosomiasis. To achieve this, we will first use satellite data to predict where tsetse are abundant, and then test the predictions by comparing the observed and expected number of tsetse caught in traps placed at various sites. Using a validated model of tsetse abundance, we will identify 'hotspots' where transmission is predicted to be high.

In selected 'hotspots' from areas where different livestock systems (pastoralist, mixed crop-livestock, zero-grazing) predominate, we will test cattle for infection with trypanosomes and the presence of pyrethroids. We will conduct a questionnaire survey of herd owners about the decision-making underpinning methods used to control tsetse- and tick-borne diseases. We will also interview owners of veterinary outlets, national distributors of veterinary medicines and government officials to gain insights into the pyrethroid supply chain.

Finally, we will use models to integrate data on the density of tsetse, prevalence of trypanosomes and use of pyrethroids to quantify the epidemiological benefit of pyrethroid-treated cattle. Empirical findings and models will form the basis of a toolbox to assist Tanzania and other countries to formulate evidence-based policies and practices for the sustainable control of sleeping sickness.

Rhodesian human African trypanosomiasis (r-HAT), caused by trypanosomes transmitted by tsetse flies, is associated with wilderness areas where tsetse and natural wild reservoir hosts are abundant. People and livestock living close to these areas are at risk of r-HAT. Studies conducted in the Serengeti District of Tanzania show that treatment of cattle with pyrethroids by livestock-keepers, to protect their cattle from animal African trypanosomiasis (AAT) and tick-borne diseases, is protecting people from r-HAT. We hypothesize that national policies to promote widespread and regular use of pyrethroids by livestock-keepers have led to large-scale control of r-HAT.

To test this hypothesis, we will:

1. Develop and test geostatistical models of the spatial correlations between satellite data and catches of tsetse from traps, to produce a high-resolution map of the predicted distribution of tsetse in northern Tanzania and identify 'hotspots' where tsetse are predicted to be abundant.

2. Sample cattle at hotspots identified in Simanjaro and Pangani Districts, where different livestock production systems (pastoralist, zero-grazing) predominate, to estimate the prevalence of Trypanosoma, using PCR-based methods, and use of pyrethroids through chemical analysis of cattle hair.

3. Conduct questionnaire surveys of livestock-keepers to assess the economic factors underpinning selection of tsetse control methods. We will also analyse the pyrethroid supply chain by conducting questionnaire surveys with retailers and distributors of veterinary medicines and government officials.

4. Use epidemiological models, parameterised with empirical data from ENABLES, to quantify the economic cost and epidemiological benefit of treating cattle with pyrethroids in different livestock production systems. Data and models will be used to produce a toolbox to help Tanzania and other countries develop evidence-based policies for the sustainable control of r-HAT and AAT.

Our project will lead to more effective control strategies for reducing animal African trypanosomiasis (AAT) and Rhodesian human African trypanosomiasis (rHAT). The potential economic and societal impacts include:

Reduced incidence of HAT
Rhodesian HAT, the zoonotic form of sleeping sickness, threatens ~12M people in East and Southern Africa. In Uganda, and potentially elsewhere, cattle act as important reservoir hosts for the trypanosomes which cause HAT. Mass treatment of cattle with pyrethroids, a proven method of controlling Rhodesian HAT, will reduce this risk.

Reduced burden of AAT
The outputs from this project will be used to improve efforts to control AAT, which kills >1 million cattle a year across 35 countries of sub-Saharan Africa. Tanzania has the third largest livestock population in Africa, and a high proportion of poor livestock keepers. More than half the country and >8 million cattle are at risk of AAT. Increasing animal productivity is likely to impact particularly on the rural poor, both in Tanzania and other affected countries.

Cost-effective strategies to control AAT
Livestock keepers in Africa spend ~$35M annually on trypanocides. In Tanzania, the annual costs of treating individual cattle with an acaricide have been estimated at $6-$36 and treatment of an infected animal with therapeutic drugs at $38. Outputs from this project will provide livestock keepers, government departments, NGOs, international (AU-PATTEC, FAO) and donor (DFID, BMGF, GALVmed) organizations with a rational basis for selecting cost-effective interventions against trypanosomiasis and an understanding of the factors influencing uptake by livestock-keepers.

Strengthening the capacity of veterinary research institutions in Tanzania
The Vector and Vector-borne Diseases Research Institute (VVBDI) provides advice to the Government of Tanzania on control of vector-borne diseases of livestock. VVBDI is broadening its original scope from a focus on tsetse-borne pathogens to encompass all vector-borne diseases of veterinary importance. This project will provide the foundation of partnerships between VVBDI and world-leading researchers from a variety of disciplines and UK institutions, thereby assisting VVBDI in its mission to support livestock keepers in Tanzania through provision of evidence-based advice to the Government of Tanzania.

Robust tourism industry
Tourism is a significant contributor to the Tanzanian economy and maintenance of wilderness areas is crucial. Increasing cost-effective control of AAT will reduce conflict at the boundaries of wilderness areas where transmission from wildlife reservoir hosts can be a source of tension between resource-poor farmers and management of national parks/wildlife reserves. 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
Uncontrolled use of insecticides and acaricides can impact on dung fauna which play an important role in maintaining soil fertility. A method of applying insecticide to cattle developed by our group (Restricted Application Protocol) reduces impact on non-target species.

ODA justification: The countries that would benefit most from improved control of AAT and r-HAT are classified as least developed (Tanzania, Uganda, Zambia) or low income countries (Kenya). The impacts listed above demonstrate the potential impacts of this project on areas closely linked to poverty and development: animal health, human health, tourism, the environment, and capacity building. Improvements in these areas will contribute to future economic development, for Tanzania in the first instance, and for other affected countries in the longer term.