Pseudogymnoascus destructans (Pd) is a cold-loving fungus that poses a severe threat to bat populations across North America. It is the causative agent of White-Nose Syndrome (WNS), a devastating disease impacting hibernating bats. Since its first detection, WNS has led to significant declines in numerous bat species, prompting widespread concern and conservation efforts.
Understanding Pseudogymnoascus destructans
Pseudogymnoascus destructans is a psychrophilic, or cold-loving, fungus, thriving in low temperatures, typically between 4°C and 20°C (39°F and 68°F). This temperature range is characteristic of the underground environments where bats hibernate, such as caves and mines. The fungus was formally identified in 2008 and later reclassified in 2013.
When cultured, Pd forms fuzzy white to brownish-grey colonies. Microscopically, it is recognized by its asymmetrically curved conidia, which are asexual spores. The fungus exhibits very slow growth on artificial media and cannot grow at temperatures above 20°C (68°F).
The Devastating Impact: White-Nose Syndrome
White-Nose Syndrome (WNS) is caused by Pseudogymnoascus destructans, characterized by visible white fungal growth on infected bats’ muzzle, ears, and wings. Beyond external signs, the fungus causes deeper damage, particularly to delicate wing membranes, which are crucial for flight, heat exchange, circulation, and water balance.
Infected bats often exhibit unusual behaviors during hibernation, such as frequent and premature arousal from torpor. This disruption leads to an accelerated depletion of their fat reserves, necessary for winter survival. Bats may also fly outside their hibernacula in freezing temperatures or be found dead or dying near cave entrances.
Physiologically, the infection leads to increased energy expenditure, dehydration, and electrolyte imbalances. These stresses result in emaciation and, ultimately, death. The disease is associated with extremely high mortality rates, often reaching 90-100% in affected bat colonies, particularly in species like the little brown bat, northern long-eared bat, and tri-colored bat. Millions of bats have died from WNS since its first documentation in 2006.
Tracing the Origin and Spread
Pseudogymnoascus destructans is believed to have originated in Europe, where bat species appear to have developed resistance to the pathogen. While Pd is enzootic in European and Asian bat populations, it does not cause significant mortality there. The fungus was likely introduced to North America through human-assisted transport, such as contaminated caving gear.
The earliest evidence of WNS in North America dates to a photograph from a cave near Albany, New York, during the winter of 2005-2006. From this likely single point of introduction, P. destructans has spread rapidly across North America. Transmission involves bat-to-bat contact and contact with contaminated environments within hibernacula. The fungus can persist in cave sediments for extended periods, contributing to new infections. As of 2021, WNS has been confirmed in 37 states and 7 Canadian provinces.
Current Research and Management Strategies
Ongoing research aims to understand the complex interactions between Pseudogymnoascus destructans and bat physiology. Scientists are investigating bat immune responses and exploring natural genetic resistance in some bat populations. Efforts also include developing potential treatments, such as probiotics or antifungal agents, to reduce fungal growth on infected bats. Monitoring the fungus’s evolution and its adaptation to different bat species and environments is also part of current research.
Management and conservation strategies focus on limiting the fungus’s spread and protecting bat populations. Decontamination protocols for cavers and researchers are implemented, requiring thorough cleaning and disinfection of clothing and gear after visiting bat habitats. Many caves and mines have been closed to public access to prevent human-assisted transmission.
Surveillance programs track WNS spread and identify new outbreaks. Habitat protection efforts, including preserving known hibernacula and summer roosting sites, support bat recovery. These efforts often involve international collaborations.