Tree die-off presents human health risk

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DURANGO, Colo., Jan. 7 (UPI) -- A recent die-off of aspen trees in the U.S. West has swelled the population of rodents that carry a virus that can be deadly to humans, researchers say.

A tree-killing syndrome called sudden aspen decline, which has wiped out swaths of trees across the West in the past decade, has changed the numbers of creatures living around the trees, including some carriers of human disease, ScienceNews.org reported.

Deer mice at hard-hit sites in 2009 were almost three times as likely to carry sin nombre virus, which can be fatal to humans, compared with mice in less-ravaged aspen stands, researchers from Fort Lewis College in Durango, Colo., said.

People inhaling virus wafting from mouse urine or saliva can get hantavirus pulmonary syndrome, a disease that kills more than one-third of its victims.

Researchers compared aspen stands and found that in places that still had most of their aspens there were more species of small mammals than in the devastated plots. In the healthier aspen stands, the most abundant small mammal found was the montane vole, which doesn't make a good host for the sin nombre virus, researchers said.

In study sites that had lost at least two-thirds of their aspens, the most abundant species was the deer mouse, which isn't as choosy about its habitat as the vole is.

Erin Lehmer of Fort Lewis College speculates infection might have risen among deer mice as their growing dominance in the landscape let them encounter each other more frequently and get into more mouse fights.

Sin nombre spreads readily among rodents through bites, she says.