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If headlines about three Montana hantavirus cases — two fatal — in two weeks sound scary, take time to learn the rest of this virus story:

Hantavirus pulmonary syndrome is a rare human disease caused by a virus common in deer mice. Prevention of HPS is simple: Keep rodents out of the house and other buildings where people live or work.

The specific hantavirus that causes the often-fatal human respiratory syndrome is called Sine Nombre virus. Last year in Montana, there were zero cases of hantavirus pulmonary syndrome.

There's still much to learn about Sine Nombre virus. Two intrepid biologists, Kevin Hughes and Teresa Rustvold, will be trapping rodents from sunrise past sundown every week until October. Swathed in protective clothing, including respirators, goggles and rubber gloves and armed with spray bottles of Lysol, the researchers will live trap thousands of mice, test and release them at sites in the vicinity of Wisdom, Gold Creek, Polson, Cut Bank, C.M. Russell Wildlife Refuge and Cascade.

The biologists have found that populations of deer mice near Cascade in central Montana have been extremely high for over a year. Since January, the hantavirus infection rate among mice trapped outdoors has been soaring.

"Nothing matches what I've seen before," said Rick Douglass, a Montana Tech biologist who has led the hantavirus research in Montana for nine years. "We've never seen numbers so high for so long."

And Douglass knows from years of research that infection rates are greater — often doubled — for mice indoors. The victims in Montana's recent HPS cases lived in rodent-infested homes.

Hantavirus information

Hantavirus Website:

CDC hantavirus automated hotline: (877) 232-3322

CDC hantavirus public inquiry phone: (404) 639-1510

CDC hantavirus public inquiry e-mail:

"Buildings are really dangerous; you absolutely have to mouse proof your house," he said.

Mouse trapping isn't the definitive answer. Mice are territorial, Douglass explained. If the mice in a building are killed, new mice will move in. The only way to end the problem is to plug all the holes quarter-inch or larger that a mouse could use to enter the building. Don't leave a door open for the dog; mice will come in, too.

Opening a cabin for the summer? Check the Centers for Disease Control Web site for advice on keeping the dust down while cleaning and disinfecting any area where rodents have been.

Montana biologist Amy Kuenzi's "mouse in the house" research has shown that some mice will enter any building they can get into. But more will come, if there's food they can reach. Using mice fitted with microchips to track their movement, researchers observed that up to 12 mice will enter a building containing food as many as 400 times a night. (If that fact doesn't motivate mouse-proofing, nothing will.)

So keep mice out of your buildings. It's not expensive. Detailed information is available at the CDC Web site.

As Douglass said of HPS: "Chances are slim of getting it, but, damn, if you do get it, your chances of dying are 30 to 40 percent."

Montanans can reduce our risk of infection from slim to almost none.