Tracking the tsetse fly
May 1, 2013
Joseph Messina, professor of geography, is the lead researcher on a National Institutes of Health-funded project to control the tsetse fly that spreads “sleeping sickness.”
Driving through a dry riverbed in Tarangire National Park in 1995, my companion and I were suddenly enveloped by a swarm of darting, hard-biting tsetse flies. We smashed our windshield in a frenetic and somewhat futile attempt to kill them with our bare hands, but were fortunate that neither of us ended up with sleeping sickness, a disease I really didn’t know much about at the time.
Sleeping sickness or African Trypanosomiasis is a parasitic disease of people and animals in Sub-Saharan Africa. Fatal without treatment, sleeping sickness killed hundreds of thousands of people during the 19th century. Not as common among people today, it however continues to impoverish many as it decimates livestock. The World Health Organization reports about 10,000 human cases per year, although I think that’s significantly underestimated with far more cases unreported. No one disputes though that sleeping sickness kills off a lot of livestock every year, clearly impacting nutrition and income.
Affecting mainly the rural poor, it is not a high profile disease and attracts little international research investment. One of the most important medicines for treatment became available only when it was discovered that it also works for controlling excessive hair growth. We have known for more than 100 years how this disease occurs and in what environments. The solution, killing off the tsetse fly, seemed entirely reasonable. Despite many attempts at clearing the bush, killing off all the wild animals, aerial spraying, and extensive trapping campaigns, the disease persists. Why? It turns out to be a problem of geography.
The tsetse fly is a speedy flier, but it reproduces very slowly. It is very much habitat dependent. Climate, land covers, and the availability of food (animals to bite) determine the location of suitable habitat. These places change. They change over space. They change over time. Sometimes they change over space and time. Tracking these changes was impossible prior to the development and widespread application of satellite remote sensing. In the past, a farmer or scientist would report the presence of tsetse and these reported places accumulated over time until the maps would show them virtually everywhere. These old maps of tsetse were sometimes right but mostly wrong.
I use satellite data produced every two weeks from NASA’s Terra and Aqua satellites to track good tsetse habitat. Now it is possible to say with some certainty which places are good habitat for tsetse. With climate models, we now can say that a particular place will become good habitat next month or in 50 years, completely changing the management of the disease system.