Why?

From the Milwaukee Journal-Sentinel, suburban development as a catalyst for disease's leap from wilderness to the human population:

Every road or subdivision we build, and even where we put a child's jungle gym and whether we use bark chips or crushed rock for walkways, can affect the risk of getting or spreading infectious diseases.

. . . . . . . .

An elderly Albuquerque, N.M., couple, for example, got bubonic plague from fleas their dog picked up during nightly walks through grasslands in the city's foothills, where plague-infected prairie dogs and rodents are common. The dog slept on their bed, giving ample opportunity for fleas to bite its owners.

If that couple had been on vacation and had returned to New York City with the dog, and if the dog's fleas had spread to rats and become established in the local rodent population, a disease that's been a problem in the Southwest could become one on the East Coast, too.

. . . . . . . .

Lyme disease is a good example of how [local planning policies that do or do not address urban sprawl encroaching on sensitive ecosystems] come into play.

The disease is caused by bacteria that live in certain mice. Ticks bite the mice, are carried on deer, and then bite humans when deer or mice come into wooded areas where there are people.

Subdivisions that fragment forests pose a double problem: They bring people into the woods, and they change the woods in a way that favors the disease.

Here's how it happens: In areas where Lyme disease is common, such as Wisconsin, about 90% of mice carry the bacteria but only about half of squirrels, chipmunks, opossums and certain birds do. Mice don't need much room to survive, but other animals do, including predators that keep mouse populations in check.

"Ticks feeding on squirrels, opossums and birds are less likely to become infected. What that means is that when you have a lot of mice and very few other species in your vertebrate community, your disease risk is very high," explained Rick Ostfeld, a scientist at the Institute of Ecosystem Studies in Millbrook, N.Y. . . . .

Ticks carry other diseases besides Lyme. And mosquitoes are spreading West Nile virus, dengue fever, even malaria, in the U.S., not just in faraway banana republics.

Hence, planners (and consumers, as well) must recognize public health risks of new development in pristine areas.