Hantavirus appeared as a mysterious lung disease in the Four Corners region in 1993. Over the next 14 years, there were 465 cases in the United States, 35 percent of them fatal.

Since 2002, Dearing's team has trapped and released about 5,000 rodents. The study is based on data collected in 2005, when the mice were studied 15 days each in spring and fall.

Researchers don't suggest eradicating the disease by killing the mice, which are vital to the wildlife food chain. But information could perhaps be used for a "risk" map so people in areas where older, bigger mice live would know to be most careful.

Dearing and Clay, who is now an assistant professor of biology at Westminster College, conducted the study with U. postdoctoral researchers Erin Lehmer and Andrea Previtali and virologist Stephen St. Jeor at the University of Nevada, Reno.

E-mail: lois@desnews.com