According to the New York Times, a decline in the aspen population occurred in 2004. As a result, the deer mice population in the same areas have increased. These deer mice are carriers of the Sin Nombre virus. Sin Nombre is a Hantavirus with a 40% fatality rate and causes about 20-40 cases each year in the United States mostly concentrated in the Southwest. Deer mice in areas that have experienced a die-back of aspens are 3 times as likely to carry the virus. The virus has very little effect on the mice themselves. Humans become infected through a respiratory route, often dirt with deer mouse saliva or urine in it.
Further loss of aspens is projected as a consequence of climate change. Increases in the population of deer mice and therefore the Sin Nombre virus are likely. This change in the threat of an infectious disease due to climate change is probably just one of the first of many similar stories we will see unfolding as we shape the environment.