Diseases resulting from deforestation and animal contact rarely call to mind a place like Duchess County, New York. Yet the county is now home to the highest rates of Lyme disease among U.S. residents. Loss of natural predators in the region's increasingly fragmented forestland has sparked a population boom in white-footed mice, which spread the bacteria via ticks that have fed off them. The same suburban development that is dicing up Duchess County woodlands for strip malls and subdivisions has created a ripe breeding ground for infection.
Intact forests are more vital to our health than we may realize. In addition to hosting a healthy diversity of species, they act as natural water treatment plants, filtering out contaminants and keeping silt out of waterways. But in places undergoing deforestation and loss of clean drinking water, there are also disease outbreaks, notes William Karesh, a field veterinarian for the New York-based Wildlife Conservation Society (WCS). Disrupted waterways often create stagnant ponds, which serve as ideal breeding sites for mosquitoes that may carry malaria. (See "Malaria Linked to Deforestation," p. 11.)
Logging roads through forests present another means for contact between humans and infected wildlife. Bushmeat hunters probing deep into Africa's jungles are thought to have first carried HIV back to their communities, and many are now regularly exposed to a "simian foamy virus" (SFV) that could also affect humans. While SFV exposure hasn't yet led to human-to-human transmission, the more frequent the "viral chatter," the more chances such viruses have to mutate into human diseases. "That's what we see with Ebola," says Karesh. "The more people there are in the forest, and the more they hunt, there's more disease transmission."
Clearing forest habitat for large-scale farming operations creates yet another disease risk. The Malaysian pig farms where Nipah virus--a previously unknown infection that has killed hundreds of people in Asia--first emerged were located near pristine rain forest, a primary foraging habitat for fruit bats that carried the disease, explains Jonathan Epstein of the New York NGO Wildlife Trust. "In traditional [small-scale] farming, the virus would run out of susceptible pigs," he points out, but at a farm with 30,000 heads the population is "large enough and dense enough to sustain an outbreak."
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