The University of Vermont


photo by Jon D. Erickson

Water scarcity creates an environment ripe for the spread of human and animal disease
by Joshua Brown

To understand how the next disease like SARS or bird flu could arise, take a trip to the Great Ruaha River. It meanders for three hundred miles through south-central Tanzania, flowing year-round from the vast Ihefu wetlands through the Ruaha National Park.

Or it used to. Starting in 1993, the river stopped running during the dry season. Some years, it's been silent for more than one hundred days.

The river offers water to the safari-famous Ruaha landscape–a grassland twice the size of Vermont that's home to lions, giraffes, endangered wild dogs, and some thirty thousand elephants. The river also has been a liquid life-force for groups of semi-nomadic farmers, including the Maasai, Barabaig, and Sukuma, who live on the borders of the park–and have relied on the river for themselves and their prized herds of cattle.

With no water in the river for several months, people and animals have a hard time finding a drink. "This has created more overlap between livestock, wildlife, and people as they all go for the same dwindling water resources," says UVM's Jon Erickson.

Cattle, African buffalo, and farmers all drinking from the same pool and living in close proximity creates a perfect opportunity for what scientists call zoonotic pathogens: diseases that can jump from animals to people, like Rift Valley fever and bovine tuberculosis.

Erickson, an associate professor in the Rubenstein School of Environment and Natural Resources, and his Rwandan graduate student, Michel Masozera, have been studying this problem in Tanzania since 2006.

They're leading one part of the HALI Project– a Swahili word for "state of health" and an acronym that stands for Health for Animals and Livelihood Improvement. It's a collaborative United States–Tanzania research effort directed by Jonna Mazet at the University of California–Davis, funded largely by the U.S. Agency for International Development. HALI includes veterinarians, water biologists, and other researchers in California as well as at Tanzania's Sokoine University of Agriculture and the Wildlife Conservation Society. Erickson and Masozera are leading HALI's socioeconomic research through UVM's Gund Institute for Ecological Economics.

"The main hypothesis of the HALI project is that water scarcity in the Ruaha ecosystem leads to the spread of diseases between humans, wildlife, and livestock," says Masozera.

"It's a big connect-the-dots kind of project, really trying to understand what are the drivers behind these diseases," Erickson says.

One of the first dots can be placed on the Ihefu wetlands. These used to work like a sponge, soaking up water in the rainy season and releasing it throughout the year to keep the Ruaha River flowing. But in the late 1980s and early 1990s, World Bank-funded canals began diverting water to irrigate rice. The wetlands and river began to dry up, aided by illegal water diversions.

Not surprisingly, pastoralists, looking for water and grass, began to take their cattle into what used to be wetlands for grazing, leading to further drying and damage. This change in land use combined with a rapidly growing population of pastoralists and small-scale farmers moving to the Ruaha park's borders and into the park itself. (It's part of a larger demographic trend expected to double the population of sub-Saharan Africa to 1.9 billion by 2050.)

In short, HALI's research has illuminated a web of connections between damaged wetlands, a drying river, degraded water quality, failing grazing land, reduced livestock productivity, disturbed wildlands, weakened wildlife, and impoverished villages–all of which means that the capacity of the ecosystem to buffer and regulate diseases–in people, wildlife, and livestock–is also damaged.

"The fundamental drivers of these new diseases are land use change, ecological degradation, population growth, and poverty," Erickson says, "We see this so clearly in East Africa, and other places in the world like Latin America."

"But how do these diseases get exchanged? Water? Fecal contamination? Traditional blood drinking?" Erickson asks, "We don't know exactly."

Which is why Erickson, Masozera, and their team surveyed 159 households, organized people to keep household diaries, and spoke with many village leaders and others around the Ruaha region over the last few years. They wanted to find out what people ate, where they got water, what diseases they had encountered, their perception of disease mechanisms, how many livestock they owned–and many other aspects of how they live.

"Our piece of HALI is figuring out where the critical interfaces are for these diseases," Erickson says. "Clearly, one is pastoralist households: they're raising livestock; living on border areas of protected areas and parks; and following traditional practices," like drinking blood and unpasteurized milk, eating raw meat, and hunting wild animals.

"It seems these pastoralist households are a key vector between diseases in wildlife populations and the rest of us," says Erickson. And that means that policies implemented in Tanzania might not only help keep Maasai nomads from getting sick and conserve African buffalo, it could help stave off the next exotic disease outbreak in New York, too.

Masozera and Erickson both use the term "one health," meaning that the well-being of humans and animals is inextricably linked–and that this shared health relies on whole ecosystems.

"This is not abstract," says Erickson, "this is the front line of the next Ebola, the next HIV."

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