When we think of testing bats at the Iowa State University Veterinary Diagnostic Laboratory (ISU VDL), rabies is the most likely pathogen that comes to mind. However, there is actually a much more serious disease affecting local bat populations known as white-nose syndrome (WNS). Unfortunately, WNS has devastated several bat species since it was first detected in North America in 2006. It has the greatest impact on bats that hibernate in groups during winter, most notably the Little Brown Bat, Northern Long-eared Bat and Tricolored Bat, all species that are year-round residents in Iowa.
The fungus that causes WNS, Pseudogymnoascus destructans, or Pd, was first detected along the eastern edge of Iowa in 2011. Affected bats were found several years later during the winters of 2014 and 2015, after which time Iowa stopped being on the leading edge of pathogen invasion.
Surveillance for the disease is usually done by surveying winter bat roosts and looking for signs of the disease but this is less than ideal for a few reasons. Surveyors may disturb overwintering bats, which can be detrimental to their health, and there is a risk of spreading the fungus, even when using appropriate precautions. Another complicating factor is that most of the significant winter bat roosts in the state occur on private land, making it difficult to identify and survey the locations. As a result, a current or comprehensive understanding of disease risk was not known.
To address the knowledge gap, Iowa Department of Natural Resources (DNR) wildlife vet, and ISU VDL affiliate associate professor, Dr. Rachel Ruden tried a new surveillance technique developed by the U.S. Geological Survey – testing bat feces. The idea behind this method is to target summer roost sites (such as bat boxes) after they become occupied during late spring. The fungus colonizes bats during the colder months when they are inactive. However, once they emerge from hibernation, they are fastidious groomers, which provides the ability to discern if bats were exposed to the fungus at their winter roosts by analyzing bat guano, or feces, through diagnostic testing.
Since 2022, the Iowa DNR has been working with county park staff, other county partners, and even private landowners, to collect guano once a week for four weeks from early May to early June. Samples are submitted to the ISU VDL, where a real-time PCR was onboarded to detect Pd using guano as the sample type. Results of the surveillance effort have been interesting. Grant support from U.S. Fish and Wildlife Service has helped screen 240 samples from 33 sites across 19 counties in Iowa, with 61 samples from nine sites across four counties testing positive (see map above). Positive Iowa counties include Buchanan, Delaware, Jones, and Muscatine, all of which had no previous baseline data. Interestingly, the pathogen has not been detected in some counties that had symptomatic bats in 2015. The current goal is to collect samples from the same sites for three years, sunsetting and onboarding new sites over time, to better understand the Pd risk landscape in Iowa for our native bats.
The success of this method of surveillance has been exciting and increases our understanding of where this deadly fungal pathogen is distributed in Iowa. To do a deeper dive into bats and white-nose syndrome you can check out the Iowa DNR’s Wildlife Disease Page or for national information, WhiteNoseSyndrome.org.
Thanks to Stephanie Shepherd with the Iowa DNR Wildlife Diversity Program for contributing to this article.
December 2025