TITLE: Emerging Infectious Disease: Geomyces destructans
AUTHOR: Rory Louderback Stratton
DATE: May 19, 2011


ABSTRACT: In 2006 a newly discovered fungal species, known as Geomyces destructans, was found in a tourist cave near Albany, New York. Microbiologists were able to classify it as a new species because it was the first Geomyces with characteristic curved conidia. This distinguished it from any fungus already documented. It was then identified as an inhabitant of France in 2009. Although excitement was an obvious emotion that overcame the microbiologists when they realized they were looking at a new species, it also caused a lot of worry. Geomyces destructans was found to be associated with the disease, White Nose Syndrome, a skin infection in which a mold covering grows on the ears, nose and wings of infected bats. This fungus is decimating colonies in the northeastern United States and Canada. It is known to affect the twenty-five species of hibernating bats and infects them during the winter season when they are hibernating in caves. This disrupts the hibernation process, causing the bats to act abnormally, resulting in death. The sharp decline in bat populations due to this emerging infectious disease, are of human interest because it would disrupt the food chain and impact our economy and food supply. Although many people seem to be frightened by this flying mammal, bats actually serve as critical players in the food chain and are also important in agriculture and pollination. It is not yet understood how Geomyces destructans emerged in North America.


INTRODUCTION: Growing up I was surrounded by all sorts of wildlife ranging from crops and trees in the garden, to domesticated animals, to all the natural inhabitants around our house. My mom taught me the importance of nature and how it is our job to protect it. I believe that no matter what the organism, they all serve a place in this world and should be respected. When I read of the fungal species, Geomyces destructans, it interested me not only because it was a newly discovered organism, but also because it was an emerging infectious disease, causing a serious decline in bat populations. Even though bats seem weird and creepy, they are still deserving of human interest and protection!
The disease caused by Geomyces destructans is termed White Nose Syndrome; it looks like mold covering the nose, ears, and wings of infected bats. Geomyces destructans spreads extremely rapidly among bat populations while they are hibernating during the winter season. The fungus is transmissible from bat to bat and also from spores in the environment. Even though the fungus was found to be an inhabitant of France after being discovered in North America, no bats migrate between the continents of Europe and North America; therefore, it is not yet known how the fungus was introduced onto this continent. Biologists are wondering if this fungus was always here and just mutated into a new destructive form, or if a human vector was involved.
Many people do not understand the importance of bats and their role in this world. I wanted to explain that bats are not just unattractive, flying mammals whose purpose is to scare people, but that they play critical roles in our lives. They are largely important in production of agriculture, the food chain, and pollination. We should try and better understand Geomyces destructans in order to preserve bat populations.




DISCUSSION:

Characteristics of Geomyces destructans:
Geomyces destructans is a psychrophilic fungus whose optimum growth temperature is between four to fifteen degrees Celsius. This is a usual year-round temperature for most caves in the United States, and caves serve as hibernacula for bats. When bats hibernate their “body temperature drops to a temperature just barely above the ambient cave temperature, falling to the range of two to ten degrees Celsius” (Volk, Blehert, and Gargas, 2009).This allows for the cold-loving fungus to grow on the skin tissue of the bats. The colonies of Geomyces destrucans grow slowly (as expected since they are psychrophilic), but have spread rapidly among bat colonies since they are in such close proximity when hibernating. G. destructans’ colonies are white, hence the name White Nose Syndrome (the disease the fungus is associated with). The diameter of the colonies varies according to the temperature they are growing at; bigger colony diameters were seen closer to fifteen degrees Celsius (compared to four degrees Celsius). This fungus belongs to the Phylum Ascomycota and produces asexual spores called conidiospores. These spores are curved which is a unique characteristic to the genus Geomyces. Conidiospores are one-celled and usually white or yellow. Another unusual characteristic of Geomyces destructans is the hyphae did not contain septa. When being cultured in the lab, G. destructans tested positive for the enzyme urease and was also found to “secrete proteinases when albumin, casein, or gelatin were used as substrates” (Chadervedi, Springer, Behr, and Ramani, 2010). Fungal species do not usually grow well on mammals, but G.destructans has been characterized as an opportunistic pathogen. This fungus is normally harmless but can become pathogenic when living among a host whose immune system is suppressed. Bats’ immune systems are suppressed when they are hibernating (to conserve energy) which may be why this fungus is successful in growing on, and infecting, the bats.


A. Colony on cornmeal agar after 16 days at 7 degrees C; B. Conidiophores with conidia in short chains; C. Conidia with seperating cell; D. Characteristic curved conidia; E. Branching conidiophores. (Volk, 2009)
A. Colony on cornmeal agar after 16 days at 7 degrees C; B. Conidiophores with conidia in short chains; C. Conidia with seperating cell; D. Characteristic curved conidia; E. Branching conidiophores. (Volk, 2009)



When, Where, and How Geomyces destructans was introduced into North America:
Because Geomyces destructans has never been seen or documented in North America before the outbreak of White Nose Syndrome, researchers wonder how it arrived on this continent. It was first discovered on February 16, 2006 in Howes Cave, a popular tourist cave near Albany, New York. Since the discovery of G. destructans, White Nose Syndrome has been documented in hibernating bat species at seventeen different locations across the Northeastern United States, and two provinces in Canada (Quebec and Ontario). The fungus has only been observed in places where White Nose Syndrome has also been detected. It is still unknown how the species came to inhabit the states. The species was found in France after its discovery in 2006 so “a plausible hypothesis for the origin of this disease in North America is introduction via human trade or travel from Europe” (Frick, Jacob, and Hicks, 2010). No bats migrate between the continents of Europe and North America so they could not have spread the fungal species between continents themselves. Some biologists wonder if G. destructans was always here and mutated into a new infectious form. Others question if humans served as vectors for the fungus, carrying it on their clothing or bags while they traveled and visited caves. Many of the sites where the fungus (and White Nose Syndrome) was documented were common tourist destinations.

The red circle indicates where WNS was first detected (New York, February 2006). The solid areas of color indicate confirmed sites where WNS was found (different color for each year since 2007). The areas of color with dots inside indicate suspect sites (areas where WNS symptoms have been reported but not yet confirmed).
The red circle indicates where WNS was first detected (New York, February 2006). The solid areas of color indicate confirmed sites where WNS was found (different color for each year since 2007). The areas of color with dots inside indicate suspect sites (areas where WNS symptoms have been reported but not yet confirmed).



Effect of Geomyces destructans on bats:
Geomyces destructans infects bat colonies during the winter season when they are hibernating. It colonizes the skin of bats by using fungal hyphae. The colonies grow and form a mold covering on the ears, nose, and wings of infected bats. The fungus destroys the tissue it inhabits, wakes up the bats, and therefore disrupts the bat’s hibernation cycle. If bats wake up early from hibernation, they use up their fat reserves prematurely and die from starvation and dehydration. Many dead bats that have been recovered from infected cave sites “contain little or none of the critical stored fat that bats must have to survive months of winter hibernation” (Wilson, 2010). Also, scientists speculate that when infected bats wake up, they disturb the other bats and cause deaths in those bats as well. Another effect White Nose Syndrome has on bats is it causes scarring of the infected tissue. These tissues are “essential for regulating physiological functions such as body temperature and blood pressure” so the scarring causes further disruption among the bats’ systems (Brown, 2009). When looking under a microscope, researchers found “no signs of inflammatory response,” indicating the bats’ bodies are not defending them against the infection (Sahagun, 2011). So far, the bats known to be affected by G. destructans are the twenty-five species of hibernating bats. The little brown bat seems to be most susceptible to the fungus and has had the biggest population decline. After the first year of G. destrucans’ discovery, there was an 85% decline in the little brown bat’s population. In certain caves, among a particular bat colony there have been 97% mortality rates. Since March 2008, “biologists estimate that over a million bats have died from the disease, many of which have been little brown bats” (USGS, 2009). Because of such rapid spreading of Geomyces destructans, and such sharp decline in bat populations, bats are at a huge risk of population extinction. Biologists still do not know how to control the rapidly-spreading fungus. They cannot use a fungicide because that could kill off other important microbes in the caves. Some people even thought to use heaters in the caves so Geomyces destructans would not be able to grow, but this too would disrupt the bats’ hibernation. In addition, removing already-infected bats would not help the situation since the fungus would just begin growing again on healthy bats. Finding a vaccine against the infectious fungus seems to be the only option. G. destructans’ extreme effects and power over bat populations demonstrates the seriousness of the issue.


The red arrows are pointing to Geomyces destructans growing on the noses of these hibernating bats (they are infected with White Nose Syndrome).
The red arrows are pointing to Geomyces destructans growing on the noses of these hibernating bats (they are infected with White Nose Syndrome).

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A - C are population trends of little brown myotis bats over the past 30 years at (A) small (<1500), (B) medium (<5000), and (C) large (>5000) hibernating colonies in the northeastern U.S. The shaded region indicates when WNS occurred. D is the population growth at hibernacula (black circles) by year since the first year of infection. (Frick, Pollock, and Hicks, 2010)

Why should we care?
Although some people say the declining bat population is just of scientific interest, it should be of interest to the entire human population since it could greatly affect our lives. Bats are critical players in the food chain and consume immense amount of insects, some of which are plant pathogens or transmitters of viruses (such as mosquitoes carrying West Nile Virus). For example, each night, one bat eats their body weight in insects. In Indiana, a colony of big brown bats has “been estimated to eat nearly 1.3 million pest insects each year, possibly contributing to the disruption of population cycles of agricultural pests” (Boyles, Cryan, McCracken, and Kunz, 2011). It is evident that bats contribute hugely to pest suppression in agriculture and declining populations increases the amount of pesticides needed. This, in turn, causes the cost of food to rise. With increased use of pesticides also come secondary consequences such as environmental damage. Insects could evolve and become resistant to the overly-used pesticides which would cause huge problems in agricultural industries; this would directly impact food availability. Recent estimates indicate that “the value of pest control provided by bats each year is at least 3.7 billion nationwide” (Sahagun, 2011). In addition to bats regulating insect populations, they also pollinate some plants including the saguaro cactus. Biologists believe there will also be many unknown consequences that come with the severe decline in bat populations, due to Geomyces destructans. Because all ecosystems or connected, the decline in bats could be potentially harmful to a handful of other organisms. G. destructans is definitely worthy of notice and its growth should be studied and monitored. President Obama actually mandated federal funding for the research of Geomyces destructans and the monitoring of White Nose Syndrome in the United States.

The Worth of Insectivorous Bats. Estimated annual value of insectivorous bats in the agricultural industry at the county level. Values (×$1000 per county). Published estimates of the value of pest suppression services provided by bats are about $74/acre. Value of bats to agricultural industry is about $3.7 billion/year. (Boyles, Cryan, McCracken, Kunz, 2011)
The Worth of Insectivorous Bats. Estimated annual value of insectivorous bats in the agricultural industry at the county level. Values (×$1000 per county). Published estimates of the value of pest suppression services provided by bats are about $74/acre. Value of bats to agricultural industry is about $3.7 billion/year. (Boyles, Cryan, McCracken, Kunz, 2011)




LITERATURE CITED:
Boyles, Justin, Paul Cryan, Gary McCracken, and Thomas Kunz. "Economic Importance of Bats in Agriculture." Science 332.6025 (2011): 41-42. Web. 14 May 2011.

Brown, Peter. "Night Stalker." Scientific American301.2 (2009): 16-18. Web. 14 May 2011.

Chadervedi, Vishnu, Springer Deborah, Melissa Behr, and Rama Ramani. "Morphological and Molecular Characteristics of Psychrophilic Fungus Geomyces destructans." PLoS ONE 5.5 (2010): n. pag. Web. 15 May 2011.

Frick, Winifred, Pollock Jacob, and Alan Hicks. "An Emerging Disease Causes Regional Population Collapse of a Common North American Bat Species." Science 329.5992 (2010): 679-682. Web. 15 May 2011.

Sahagun, Louis. "Fungus Sweeps Across the Country, Killing Bats." L.A. Times (2011): 1-2. Web. 14 May 2011.

United States. White Nose Syndrome (WNS). Reston, VA: , 2009. Web. 14 May 2011. http://www.nwhc.usgs.gov/disease_information/white-nose_syndrome/

Volk, Tom, Blehert David, and Andrea Gargas. "Tom Volk's Fungi." Geomyces destructans, a Fungus Associated With Bat White Nose Syndrome (WNS). N.p., 18 June 2009. Web. 13 May 2011

Wilson, Zac. "White Nose Syndrome: Could Cave Dwelling Bat Species in the Eastern U.S. Become Endangered in Our Lifetime?." Bat Conservation and Management (2010): 1. Web. 14 May 2011.