Introduction
White-nose syndrome (WNS) is a disease caused by the exotic fungus Pseudogymnoascus destructans that kills bats (Foley et al., 2011). WNS has been reported to cause high death rates and significant population decline in bats, and scientists predict the regional extinction of certain species. This fungus thrives in cold places, often when bats hibernate during the winter. During these cold periods, bats reduce their metabolic rate; thus, body temperatures are relatively low to save on energy levels, making them prone to infection. Once infected, the hibernating bat often wakes up to warm, or high temperatures that force it to use up its fats reserves. Consequently, the bat starves before it can replenish its energy during the springtime (Foley et al., 2011).
Factors that make bats more susceptible to WNS
Researchers report that the disease manifests through visible whitish growths on the infected muzzles and wings of the bat. In some cases, infection leads to tearing or thinning of the wing membrane, which hampers the bat’s ability to fly or look for food. WNS significantly affects the bat’s immune system making it more susceptible to other infectious diseases (Foley et al., 2011). These visible signs of the disease appear in the later stages of nearing death. The infected bat wakes up more often, thus using twice as much energy as the healthy bats. WNS fungus is transmitted through physical contact between infected bats and beneficial bats. Additionally, bats can pick up infections from the surfaces of the mines or caves where they hibernate (Foley et al., 2011). Human beings can unknowingly transmit the fungus from WNS infected sites to WNS-free sites through their shoes, gear, or clothing. However, there have been no reported cases of human WNS infections.
The spread of WNS among bats is directly related to the type of hibernaculum. Hibernation sites near substantially hazardous areas or areas that were previously WNS-infected increase the risk of infections. The fungus flourishes in underground shelters that are cool and moist (Wilder et al., 2011). Such shelters include caves and mines with low, cold temperatures just above freezing air temperature. Research shows that caves are riskier for bats than mines since mines are relatively new habitats; thus, the pathogens may be yet to be introduced.
Moreover, these places provide high humidity, reducing water loss in bats during hibernation. The size of the cave, depth, number of openings, elevation, airflow, and water infiltration are factors that either reduce or increase the temperature of the underground shelter favoring the hibernation of the bats (Wilder et al., 2011). In most regions, annual atmospheric temperatures are not within the optimal range for the fungus to grow; thus winter period is the most favorable. The climate within the individual cave makes the condition more conducive than others, thus attracting the fungus. It is observed that bats in these areas exhibit unusual behavior such as flying in the open cold weather, moving into colder parts of the cave, or flying during daytime.
The size of the colony also affects the rates of infection. Large colonies experience more illnesses and deaths than smaller colonies. More bats occupying a hibernaculum increase the likelihood that the pathogen will be introduced. Consequently, the density of hosts carrying the pathogen increases; therefore, contact rates between the infected bats and the healthy bats go up (Wilder et al., 2011). Suppose the bats hibernate in sites with optimal conditions for the growth of the fungus. In that case, the colony’s size will affect the rate at which the pathogen multiplies, thus increasing mortality rates.
The composition and diversity of the bat species present in a hibernaculum also influence the infection rate. Some species are more susceptible, while others are more resilient to the disease. The Indiana bat has been listed as an endangered species since WNS related death rates have threatened to wipe out its population. Despite being genetically resilient to the disease, the little brown bat has suffered significant population declines. The Northern long-eared myotis native to North America have been removed from all infected areas to preserve the species. However, the Gray Bat species and the Virginia Big-eared bat species’ have suffered relatively low death rates compared to other species (Wilder et al., 2011).
Conclusion
WNS has direct effects on bat populations by significantly reducing their numbers. This severe decline impacts the biodiversity and ecosystem throughout the country. The speed at which WNS is eradicating the once million bat population is such that it is challenging to recover or repopulate in the future. This poses a significant threat to other sectors such as agriculture, wildlife, and forestry. Since many insects go uneaten, farmers face the high financial burden of pest control and crop damage (Foley et al., 2011). Aggressive efforts into research and innovation to secure bat habitats to stem any future losses from any form of transmission are required to prevent the total extinction of bats.
REFERENCES
Wilder, A. P., Frick, W. F., Langwig, K. E., & Kunz, T. H. (2011). Risk factors associated with mortality from white-nose syndrome among hibernating bat colonies. Biology Letters, 7(6), 950-953.
Foley, J., Clifford, D., Castle, K., Cryan, P., & Ostfeld, R. S. (2011). Investigating and managing the rapid emergence of white‐nose syndrome, a novel, fatal, infectious disease of hibernating bats. Conservation biology, 25(2), 223-231.
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