Foreclosure Fallout: Public Health Threat

May 21, 2008 — -- California's Contra Costa County, in the suburbs of San Francisco, is the heart of foreclosure country. Its streets are dotted with examples of the American dream abandoned.

Thousands of sprawling ranch homes stand unoccupied, along with thousands of now stagnant swimming pools. And a nasty unforeseen consequence of the housing downturn has bubbled to the surface in those pools: mosquitoes.

"Pools, when they aren't maintained, there are nutrients in the water and you get the sun producing energy and the mosquitoes will use the bacteria or the energy to produce," said Chris Miller, a biologist with the Contra Costa Mosquito Vector and Control District.

But these mosquitoes are not just a mere nuisance, they're also potentially dangerous.

"They transmit West Nile virus," said Miller, "and that is why we are so concerned with these pools and the foreclosure issue. It can be a real threat to public health."

Miller thinks he has the solution to the mosquito problem. His answer is a tiny fish with a big name: Gambuzia Affinis.

"These fish work 99 percent of the time," Miller said.

The newest soldiers in the foreclosure war grow no more than 2½ inches, but they are mean. These cannibalistic fish also love to eat mosquitoes -- lots of them.

"They are surface-oriented fish, so they feed on surface-oriented insects," Miller said. "They feed primarily on mosquito larvae, which go to the surface to breed, so they will intersect them at the surface. They also eat wind-blown insects."

And the fish have quite an appetite. "Probably an adult female can eat 500 mosquitoes a day," Miller said.

That sounds like a lot, but mosquitoes multiply at a rapid rate. They can mature from egg to adult in five days at the height of summer and they need very little water to do so.

"Mosquitoes can breed in two or three millimeters of water," Miller said. "So a situation like [a swimming pool] is prime for breeding mosquitoes."

Miller has set up a prime breeding area of his own for the fish whose sole purpose is to control the mosquito population. Since last year he has increased the fish capacity by 210 percent.