White-nose syndrome (WNS), caused by the fungal pathogen Pseudogymnoascus destructans, has killed over 6 million North American bats since its detection in 2006 - the most catastrophic wildlife disease event ever recorded in North America. The fungus invades wing and nose tissue during hibernation, disrupting thermoregulation and causing premature arousal that depletes fat reserves. Affected bats exhibit distress behaviours, emaciation, and mass mortality. Some species face functional extinction: little brown bat populations declined 90%+ in affected areas. Welfare implications include prolonged suffering during disease progression, mass mortality in hibernacula, and ecosystem disruption affecting insect pest control valued at billions annually. Research into biocontrol (Rhodotorula mucilaginosa probiotics), UV light treatment of hibernacula, and selective breeding for resistance is ongoing. WNS has now spread to 38 US states and several Canadian provinces.