A fungus associated with major bat mortality that was first spotted in New York in 2006, and confirmed in 2007, continues to spread. It has now been found in 9 states. The threat could possibly spread to much of the eastern half of the country, as well as a few Canadian provinces.
The deaths of about 400,000 bats already, and potentially millions more if the problem continues unchecked, could have a substantial impact on the environment, since it would reduce the presence of an animal that plays an important role in tasks such as controlling insect populations and pollinating plants. At least two of the bat species, the Indiana bat and the Virginia big-eared bat, are on the list of endangered species.
The fungal problem, called white-nose syndrome, after the white fungal patches that appear on the nose and wings of some infected bats, is associated with deaths of 90-100% of the bats in some settings. The identified fungus may be the culprit, or it may be an indicator of another culprit or set of culprits.
The outbreak is also having an indirect effect, as recreational caving is forbidden or restricted  in an increasingly wider geographic range, affecting hundreds of caves.
The states with documented cases include CT, MA, NH, NJ, NY, PA, VA, VT, and WV. The states of DE, MD, and WI are also participating in related research. The current theoretical range of expansion includes about 16 other states, from the upper Midwest to the southeast and central south (AL, AR, GA, IA, IL, IN, KY, ME, MI, MN, MO, NC, OH, OK, SC, and TN), as well as Ontario and Quebec. The cause of the outbreak remains unknown, but considerable research is under way. Climate change is being considered as a contributing factor, but has not been proven to be a culprit so far, according to the US Fish and Wildlife Service.
This particular fungus appears never to have manifested itself in this way anywhere in the world prior to the appearance of this problem in the US. However, a potentially similar fungal outbreak was spotted in Europe in the early 1980s, and documented in 2001-2003. Cases have been seen in the Czech Republic, France, Germany, the Netherlands, Romania, and Switzerland. For more information on these cases, contact USGS's Paul Cryan at 970-226-9389.
Affected US bats tend to be emaciated and dehydrated, and their hibernation behavior is altered. For instance, some leave their cave or abandoned mine during the day, when their insect foods aren't available. Others try to hibernate in an unusual part of a cave, such as near the mouth, which can be colder.
Your stories can be linked to specific incidents, or to research and attempted control and mitigation measures. People involved in those efforts can be found in dozens of state agencies, and with interest groups that focus on either bats or caves. Sources include:
- US Fish and Wildlife Service:  Diana Weaver,  413-253-8329.
- State wildlife agencies. 
- USGS National Wildlife Health Center. 
- Bat Conservation International. 
- Northeastern Cave Conservancy, March 29, 2009, press release. 
- The National Speleological Society. 
- USFWS list of organizations involved,  including the above, as well as those in many other states, such as CA, IN, KY, MD, MI, and OH, in the Canadian provinces of New Brunswick, Ontario, and Quebec, and even Disney World.