“The prevalence at the Durango site was about 50 percent, and that’s the highest we’ve ever seen,” said Charles Calisher, professor of biology at Colorado State University. “It’s ranged from zero over a couple of years – actually, we got plenty of mice with no virus for a couple of years – but the prevalence is usually 14 to 20 percent, something like that. A couple times it will jump up to 40 percent, 30 percent, something like that. Here, it was 50 percent.”

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