Fighting the fly: drivers of disease in the Zambezi valley

The battle against the tsetse fly in the Zambezi valley is a long and continuing one. The fly is the source of both animal and human trypanosomiasis – nagana in cattle, sleeping sickness in humans – and is one of the reasons why the valley has been only sparsely inhabited until recently.  But the relationship between the fly, livestock, wildlife and people appears to be changing, with new transmission dynamics unfolding, potentially with dangerous consequences.

A new project, led by the University of Zimbabwe, with the Tsetse Control Branch in Veterinary Services in the Ministry of Agriculture, and working with the STEPS Centre at Sussex and the Universities of Edinburgh and Southampton, is trying to get to grips with the ‘dynamic drivers of disease’ that affect who and what gets infected and where.

Conquering the fly and pushing back the fly belt was seen from the colonial era as one of the great civilising efforts of colonial development. Tsetse control was seen as a prime reason for intervention: clearing vegetation, exterminating wildlife, moving people, often in draconian ways. Yet others see the fly as the saviour of wilderness, and key to conservation of remote, biodiverse landscapes, protecting such areas from encroachment by people and their animals. The fly in other words is at the centre of the classic tussle between visions of civilisation and modernity and conservation and preservation, reflecting conflicting values, perceptions, politics and interests.

The social, ecological, political and economic consequences of the tsetse fly are therefore profound, raising fundamental debates about how people and disease interact in complex ecosystems. In his classic book, ‘The Role of Trypanosomiases in African Ecology: A Study of the Tsetse Fly Problem“, published in 1971, John Ford – a scientists centrally involved in colonial control efforts – explored some of these debates, and challenged what he described as the ‘colonial doctrine’ of tsetse control, based on an ecological understanding of disease dynamics. Forty years on, the dilemmas of fly control persist today, with some important new contexts.

In our study area in Hurungwe district in Zimbabwe, a number of cases of human sleeping sickness have been confirmed in recent months. These are unusual in Zimbabwe, although reporting is often poor, so official data is misleading. When people become sick and die, the usual diagnosis is malaria. Scientists are wondering has something occurred in the ecology of the area to increase human infections? There are other puzzles too. Dissections of tsetse flies at the government’s Rukomichi research station, in the heart of the tsetse belt in the Mana Pools National Park, show very few T. brucei rhodesiense trypanosomes, the ones that cause the disease in humans. Yet blood samples taken from cattle outside the park, show much higher incidence. And now humans are dying too. What is going on?

The new research is trying to investigate. Is it changes in rainfall and climate patterns affect fly distributions and behaviour? Is it changes in vegetation and land use, influencing livestock-fly interactions? Is it changing settlement patterns, with people moving into wildlife areas, and coming into contact with wildlife disease hosts and fly vectors? Is it changes in wildlife movements, as they seek water and grazing outside the park? Is it changes in human behaviour and susceptibility as new people come to the valley in search of farm land for elsewhere in the country?

Unfortunately, we simply don’t know the answers to any of these questions, and so cannot suggest what disease control strategies might work. There has of course been masses of work on tsetse and trypanosomiasis in Zimbabwe, part of long-term research and development programmes. But much of this has been very targeted – on fly behaviour, chemical control, and trap design, for example. While this has been enormously important in developing effective, low-cost control approaches, it has often not looked at the underlying ecological, social and economic drivers. This holistic, integrated, cross-disciplinary perspective is of course not new. John Ford was a great advocate of this from the 1960s, but it is only recently that a ‘One Health’ approach to emerging (and in this case re-emerging) infectious diseases has become central to policy debates.

Our new research, working closely with colleagues in Zambia on the other side of the Zambezi, aims to come up with new perspectives on what is going on. It is an important, but difficult challenge, and one that requires dedicated cross-disciplinary science to tackle. Watch this space for some results over the coming few years.

This post was written by Ian Scoones and originally appeared on Zimbabweland