Researchers predict 2006 will be a worse year for hantavirus cases than last year was in the Four Corners region where Arizona, New Mexico, Colorado and Utah meet.
Scientists at the University of New Mexico and Johns Hopkins Bloomberg School of Public Health have been studying the situation.
They also warn that parts of southern Colorado and north-central New Mexico, previously at low-risk for the virus, also face an increased risk.
Four cases were reported in the Four Corners region last year.
This year, conditions are similar to 1998 and 1999, when there were six and eight cases.
The disease is spread through the dried droppings of infected rodents, especially deer mice.