STRESS-MALAWI: Strengthening Resilience against Sleeping Sickness in Malawi

Predicting, detecting and responding to outbreaks of known and emerging infectious diseases pose a worldwide problem, particularly in countries where the health system is fragile. In sub-Saharan Africa, outbreaks of established and emerging (e.g. Ebola) zoonotic diseases often have their origins in remote wilderness areas where pathogens circulate largely undetected between wild reservoir hosts and with few human cases. For reasons poorly understood, the transmission dynamics of these pathogens can change and outbreaks occur as the disease spills over into neighbouring populations of humans and livestock.

Rhodesian Human African Trypanosomiasis (rHAT), caused by Trypanosoma brucei rhodesiense transmitted by tsetse flies, is a zoonotic disease associated with conservation areas of East and Southern Africa. In 2019-20, Malawi experienced a surge of rHAT cases. In a period of just three months, the number of cases was triple the annual mean for the previous decade, with most cases coming from communities located near two national parks. The underlying causes of the surge are uncertain but potential causes include changes in the ecology and behaviour of tsetse as a consequence of environmental changes, and/or the emergence of a virulent strain of Trypanosoma brucei rhodesiense.

Currently, control of rHAT in Malawi relies largely on passive detection and treatment of cases. There are no vaccines or drugs to prevent rHAT and the only way of protecting people is by controlling tsetse flies, however, to do this across a national park is prohibitively expensive and logistically complex. More affordable and sustainable strategies which remove tsetse from settled areas and confine them to the park are needed.

The overall goal of the STRESS-MALAWI project is to test the hypothesis that risk of rHAT for communities living on the edge of conservation areas can be reduced by focusing tsetse control efforts on the key ecological zones which sustain the tsetse populations biting humans. These zones are likely to be the edges of a conservation area where dense natural vegetation and an abundance of wild hosts sustain high numbers of tsetse relatively close to settlements.
Focusing on the Vwaza Marsh Wildlife Reserve in northern Malawi, and the surrounding farming areas, we will undertake empirical and modelling studies to quantify the underlying spatial and temporal drivers of rHAT and identify potential causes of the 2019-surge in cases. Findings from these studies will allow us to design and deliver a cost-effective and spatially-informed tsetse control strategy in which insecticide-treated targets, which attract and kill tsetse, will be deployed to protect communities from rHAT. To achieve our goal, we will:-

First, develop and implement a tsetse sampling strategy to quantify the population dynamics of tsetse and trypanosomes across the interface of conservation and agricultural areas. Tsetse will be sampled along transects across the interface and simultaneous mapping of landcover using satellite and drone imagery will quantify the relationship between tsetse abundance and vegetation.
Second, quantify the numbers and type of tsetse attracted to humans moving outdoors and within buildings and hence identify where and when people are likely to be bitten.
Third, determine whether the transmission potential of T. b. rhodesiense has increased due to the emergence of a new virulent strain of parasite.
Finally, we will integrate knowledge from 1-3 to design and implement a vector control strategy at the interface of the Vwaza Marsh Reserve.

Our findings will contribute to the development of a strategy for monitoring and control of rHAT in Malawi and other countries in East and Southern Africa. More generally, the data, models, trypanosome genomes and methods produced by our project will contribute to evidence-based strategies for controlling existing and emerging vector-borne zoonoses associated with wilderness areas.

Rhodesian human African trypanosomiasis (rHAT) is caused by the protozoan parasite Trypanosoma brucei rhodesiense via the bite of infected tsetse flies. Foci of this disease persist in areas where tsetse and wild reservoir hosts are abundant (e.g. national conservation parks of Central and East Africa). People and livestock living closest to these areas are at the highest risk of contracting rHAT, but due to its zoonotic lifecycle it is extremely difficult to prevent transmission without targeting the vector.

The Vwaza Marsh Reserve spans the border of north Malawi and Zambia and experienced an unexpected surge in rHAT cases in 2019-20. The reasons for this rise in rHAT are currently unknown but the majority of cases originated in villages less than 5 km from the park. We hypothesize that evidence-based and spatially explicit targeted vector control surrounding the park edge can reduce the risk of rHAT spilling into neighbouring agricultural areas.

To test this hypothesis, we will:
1. Sample tsetse along transects across the wildlife-agriculture interface and other potential tsetse habitat outside of the park and quantify the relationship between abundance and the environment using data captured by satellites and drones.
2. Quantify the human-biting index of local tsetse flies in Vwaza and determine whether exposure to tsetse-bites is greatest either inside or outside households via comparative entomological sampling methods.
3. Compare the genetic structure and parasite virulence of T. brucei rhodesiense circulating in Vwaza with historical samples of the parasite
4. Implement a two-year tsetse control strategy on the borders of the Vwaza Marsh Wildlife Reserve by deploying insecticide-treated targets at optimal densities informed by computational models of tsetse population dynamics.