Scientists are warning that this could be a bad year for a rare but often fatal viral infection spread by rural rodents, especially in the western U.S.
By the end of May, the Centers for Disease Control and Prevention listed 18 confirmed or suspected cases of hantavirus in nine states. Eight patients were from Arizona, Colorado and New Mexico -- high for that region.
"All it takes is one infected rodent," warned Dr. James Mills of the CDC. Additional infections have since been reported, but Mills could not provide details.
"Hantavirus pulmonary syndrome" is a severe respiratory infection spread by rodent urine, feces or saliva. You don't actually have to touch a rodent. People typically become sick about two weeks after breathing virus particles stirred up in a rodent-infested space, such as when sweeping a mouse nest out of a barn or cabin.
Hantavirus isn't carried by big-city rodents, but by four species of mice and rats that live in rural areas around the country.
Rangers are warning visitors to national parks not to feed or handle rodents, after a 7-year-old boy played with a possibly infected deer mouse he caught on California's remote Channel Islands.
Hantavirus-carrying mice can slip into a house, barn or vacation cabin through a crack just a quarter-inch wide, so knowing how to safely deal with rodents is important.
Hantavirus infection kills 43 percent of its victims but fortunately it's fairly rare. Only 217 U.S. cases have been confirmed since the first U.S. hantavirus strain was discovered in 1993, during a mysterious outbreak in the "Four Corners" region of the Southwest that killed at least 26 people.
The risk of hantavirus seems to fluctuate with climate. The West has the most hantavirus, and CDC last year discovered a bumper crop of deer mice there, thanks to a warm winter and high rainfall from the climate phenomenon El Nino. But most of those new mice were uninfected babies.
This year, rodent populations aren't quite as high -- but a lot of older mice still alive from last year's baby boom have now caught hantavirus and become a threat. About 40 percent of mice in parts of New Mexico and Colorado are infected, far more than the typical 10-15 percent mouse infection rate.
But the CDC says the real risk usually comes indoors, when people find the weekend cabin they rented was a mouse's winter home or clean out a barn or other infested area. Advice from health officials:
- Air out unused cabins before occupying them.
- Before cleaning infested buildings, spray nests, droppings and other signs of rodents with a disinfectant or bleach solution, which can kill hantavirus. Avoid stirring up dust until the area is wet. Then sweep up while wearing rubber gloves and discard the mess in sealed bags.
- Whether at home or camping, keep food and garbage sealed to avoid attracting rodents. Also, seal cracks in dwellings, keep brush away from foundations and elevate hay, wodpiles and garbage cans to deter rodent nesting.
- When outdoors, don't disturb rodent burrows or droppings, or camp near rodent dens, woodpiles or garbage areas that might conceal nests, the park service said.