Rest easy, Utah County: The sentinel chickens are in place.

"They are a great early warning system for us," said department spokesman Lance Madigan.

About 450 chickens from a Nephi farm were distributed across the state to be placed in areas where health officials expect the virus to appear first. Utah County received 20 birds, which were placed in groups of five at the top, bottom, and middle of the county -- including two groups near Utah Lake, a known mosquito breeding ground. The chickens are then tested weekly for the virus to give officials an idea of where it's spreading. Because the birds are kept outside constantly in places with known mosquito populations, the virus generally shows up in them several weeks before it hits the human population, Madigan said.

"It gives us more than just a blip," he said. "It gives us a progression and some history."

The county has heard nothing negative from animal rights groups about the use of chickens, Madigan said.

"We treat them as humanely as possible," he said. "They carry the disease but don't often die from it."

When a chicken tests positive for the virus, the department responds immediately with heavy spraying in the area near the cage, said Mosquito Abatement Director Bob Mower. They use a chemical called Aqua-Reslin that kills adult bugs on contact.

The chickens are one of two early warning systems the Health Department sets up each summer, Mower said. The other involves 15 mosquito traps around the county from which the bugs themselves can be tested for the virus. Officials place dry ice into the traps, which draws mosquitos to the carbon dioxide that is emitted when the ice vaporizes.

Mower said both tests are critical because they generally clue in officials about where the virus is headed around the first of July. The virus doesn't usually manifest in humans until a few weeks later because of warming weather and the popularity of outdoor plans, he said.

"That seems to be when the first cases come down," he said. "As you get into July, you get lots of those."

August and September generally bring the highest number of cases, he said.

Last year, only one chicken contracted the virus in Utah County. That was way down from 2006, when 23 tested positive. Mower said he can only guess why that was.

"We had a dry year last year," he said. "It's been interesting to watch the pattern of it."

Statewide, positive tests in chickens dropped from 111 in 2006 to 74 last year. The number of infected horses and wild birds also fell to about a third from one year to the next.

The story is the same for humans. Almost 160 were infected statewide in 2006, while just 68 were in 2007. In the county, it was 65 in 2006 and only two confirmed cases in 2007. That's good news because about 20 percent of cases show up with flu-like symptoms and 1 in 100 infected people can suffer neurological damage and even die -- as five people did in Utah in 2006, Mower said.

In recent years, the virus seems to have been moving from the south end of the state to the north, Mower said. But because of the heavy winter, things could be different this year, he said.

"I've been interested to see what's going to happen with our extra snow," he said. With more snow comes more standing water, which is a favorite breeding ground for mosquitos, he said.

In the west, one human has already tested positive this year in Arizona, according to the Centers for Disease Control and Prevention. Infected animals are also showing up in California.

Madigan recommends wearing light-colored clothing and lots of mosquito repellent if you're going to spend much time outdoors. And stay away from standing water -- it's virtually a guarantee that mosquitos will be lurking about, Mower said.

"There's just thousands and thousands of those through the community," he said. "Backyard ornamental pools are a nightmare."

As for the chickens, when mid-September rolls around, they'll be ready to retire. The department plans to sell them to farmers for use as laying hens, Madigan said.