Bats are much maligned with their age-old association with Dracula, vampires and rabies to more modern concerns, such as the proposed source of several emerging viral diseases including Ebola virus, Middle Eastern Respiratory Syndrome coronavirus, and Nipah virus, to name a few. Yet, what is less known is the important role that bats play in providing ecosystem services and the fact bats are also victim to one of the most devastating wildlife diseases ever discovered.
Bats are a unique group of mammals of the order Chiroptera whose forelimbs form webbed wings, making them the only mammals naturally capable of true flight. They are also the second largest order of mammals (after rodents), representing about 20% of all classified mammal species worldwide, with over 1,300 species. Bats are present throughout most of the world, with the exception of the cold, polar regions. The majority of bat species are insectivores, and the remainder is mostly frugivorous, with a few specialist feeders such as the vampire bats that feed on blood. Given the wide distribution and the fact they occupy many ecological niches, bats play important roles in providing ecosystem services. Fruit and nectar-feeding bats are critical pollinators for a wide variety of plants of economic and ecological value, including the agave plant from which tequila is made. In addition, many tropical plant species depend entirely on bats for the distribution of seeds. And bats are primary consumers of insects, many of which are pests for forest products and agricultural crops. A recent economic analysis indicated that insect suppression services provided by bats to U.S. agriculture is valued between $4 to 50 billion dollars per year.
Unfortunately, bats are victims of diseases too, and for the past decade we have witnessed devastating losses of species of bats in North America due to white-nose syndrome (WNS). White-nose syndrome is an emerging disease of hibernating bats that has spread from the northeastern to the central United States at an alarming rate. Since the winter of 2007-2008, millions of insect-eating bats in 25 states and five Canadian provinces have died from this devastating disease. The disease is named for the white fungus, Pseudogymnoascus destructans (Pd), that infects skin of the muzzle, ears, and wings of hibernating bats. The fungus was discovered through innovative scientific detective work by the USGS National Wildlife Health Center. Pseudogymnoascus destructans, is a recently described, cold loving fungus, and this is first time a species from this genus has been identified as a pathogen of vertebrate species.
The USGS National Wildlife Health Center (NWHC) is a US government research facility with a dedicated mission of safeguarding wildlife and ecosystem health through dynamic partnerships and exceptional science, and seeks to protect wildlife from health threats by understanding the causes and drivers of diseases and developing strategies to prevent and manage them. Through a comprehensive program involving broad biomedical and ecological expertise and capabilities, the NWHC investigates disease outbreaks, conducts active surveillance, performs applied research, and provides management tools to address these threats. Scientists at the NWHC represent a wide array of expertise and capabilities, including wildlife biology, ecology, statistics, quantitative modeling, microbiology, veterinary medicine, epidemiology, toxicology, molecular biology, and immunology.
The NWHC along with the U.S. Fish and Wildlife Service and other partners continues to play a primary role in WNS research. Additional studies conducted at NWHC led to the development of standardized criteria for diagnosing the disease, and scientists at the NWHC have pioneered laboratory techniques for studying impacts of the fungus on hibernating bats. As more is learned about the ecology of WNS through a greater understanding of the interactions among bats, fungi, and the environment, new opportunities may arise to interrupt the disease cycle. NWHC is actively investigating vaccination and other strategies to control environmental reservoirs of the fungal pathogen as a means by which to manage WNS in hibernating bats.
Current estimates of bat population declines in the northeastern US since the emergence of WNS are approximately 80%, and some species have been predicted to go locally extinct in 20 years. The northern long-eared bat has also been listed as threatened by the U.S. Fish and Wildlife Service as a direct consequence of WNS. This sudden and widespread mortality associated with WNS is unprecedented in hibernating bats, among which disease outbreaks have not been previously documented. It is unlikely that populations of bat species affected by WNS will recover quickly because most are long-lived and have only a single pup per year. Consequently, even in the absence of disease, bat populations do not fluctuate widely in numbers over time.
The true ecological consequences of large-scale population reductions currently under way among hibernating bats are not yet known; however, as noted earlier farmers might feel the impact due to the loss of insect suppression services. There may be other ecological repercussions that are difficult to anticipate, and this disease illustrates an important tenet of EcoHealth that loss of biodiversity jeopardizes the ecosystems upon which all life depends.
Thus, as you drink your margarita and look up at the night sky and see what may be dwindling numbers of bats, think of Batman and not Dracula. Bats are the heroes of the night sky, and not the villains. This dual identity of bats is a challenge; however, we must find ways for bats and people to co-exist if human, animal, and wildlife health is to be sustained.
USGS National Wildlife Health Center Web site: http://www.nwhc.usgs.gov/
White Nose Syndrome Web site: https://www.whitenosesyndrome.org/
Bat Conservation International Web site: http://www.batcon.org/