Bat White-nose Syndrome: There is a New Fungus Among Us By Dr. David Blehert


Dr. David Blehert:  Thank you, Bill, for
the very nice introduction and thanks to Hannah Hamilton for inviting me and the USGS communications
group for arranging my visit. So today, I’m going to talk about bats and
new bat disease.  Let’s see if I can my slides to advance.  Can everybody hear me OK? Audience:  Yes. Dr. David Blehert:  Let’s see.  Yeah. 
The arrows.  They should work.  There we go. OK.  So let me just begin by saying a little
bit about bats to get us all on the same page.  Bats are the only mammals that are capable
of self-powered flights.  Most are nocturnal.  Perhaps these adaptations of being one of
the few animals that’s out flying in the night sky when there’s otherwise lack of aerial
predators has afforded this group of animals with the evolutionary opportunity to diverge
into a huge number of species. Bats are the second most species diverse group
of mammals on the planet.  Only behind rodents.  There are about 1,100 species of bats out
of a total 5,500 or so species of mammals.  And just an amazing amount of adaptations,
if you look at this giant fruit bat on the screen here, this animal consumes ripe fruit. 
This is nectar-feeding bat that can hover in front of cactus flowers and lap the nectar. Here’s a bat that’s got both white and black
fur.  It’s the spotted bat in the American Southwest.  With his huge ears, I think this
animal is known to forge for insects on the ground and they can say that it can actually
hear their footsteps. And here we have a bulldog bat — which actually
eats fish and it catches them right out of the water. So, to transition the topic of today’s talk,
a disease bats, white-nose syndrome is a fungal disease.  Of all the various pathogens or
disease agents that we know of, and I’m a microbiologist so I know of a lot of these,
even for microbiologist, fungi are not often the first that come to mind when talking about
disease. When it comes to disease of humans, there
are really only six major recognized groups or genre of fungi that cause disease and to
name them, maybe you’ve heard of some of them, includes the Yeast Candida and other fungi
Aspergillus, Histoplasma, Blastomyces, Coccidioides and Cryptococcus.   But, that’s six out of literally hundreds
of thousands of species.  Despite fungal pathogens not necessarily being the first
thing that people think of when talking about disease, it’s indisputable as I’ve outlined
on this slide here, that fungi have had major impacts on the world.

So for example, fungal
diseases transformed landscapes by ravaging both American chestnut trees and elm trees,
all within the 20th century.  The Irish potato famine caused by a fungal-like organism that’s
now referred to as called Oomycete, caused the death and immigration of over 2 million
people. Fungi remain potent pathogens of plants, humans
and wildlife today, yet fewer than 10% of all fungal species are known to science. 
There are limited antifungal therapeutic drugs available and they often have associated toxicity
because of terms of classes of animals, fungi are actually very closely related to people. 
So when we target bacterial pathogens with antibiotics, we’re targeting mechanisms of
replication for that microorganism that are distinctly different than those in our own
bodies. When it comes to treating a fungal pathogen,
there are also what are known as eukaryotes just like us.  And so it becomes challenging
to kill the fungus without harming the host.  There’s no antifungal vaccines.  And then
when it comes in particular to plants or animals, like wildlife, that don’t have intrinsic or
obvious economic value, disease management can be very challenging. 

Another point
of interest is that fungal diseases in humans and other mammals are most commonly associated
with hosts that have compromised immune systems.  So there’s something else going on.  Or,
in cases where that host was exposed to a huge dose of the organism. Say, through, fungal
diseases sometimes arise in military personnel doing training exercises where they’re crawling
through soil with their faces close to the soil that’s enriched with fungal spores of
certain disease agents. This graphic shows that with respect to human
health– and likely driven changes in host’s immune status– caused by the emergence of
HIV, increased use of immunosuppressive medications like steroid treatments, other intensive care-based
therapies that have people in hospitals with in-blowing catheters that are providing a
conduit between the outside world and the inside of the body, incidents of systemic
fungal disease and people has been exponentially on the rise since about the 1950s. As I move along through this presentation,
and along these same lines, I hope to convey to you the unique world that hibernation plays
in white-nose syndrome as one of these predisposing factors to this novel of disease.

So what
is White-nose Syndrome? It’s an emerging fungal disease of bats and
it’s a very interesting– or maybe insidious would be a better word — disease because
bats are specifically infected with this fungus when they hibernate; which, based on research
done in other hibernating mammals, is believed to be, it’s known to be in these other mammals,
and we believed it to be in bats, to be a time of natural immunosuppression.  So, there
is one of the potential predisposing factors. Furthermore, a large scale disease epidemic,
or we’d say epizootic when we’re talking about mammals, a large scale epizootic among bats
like White-nose Syndrome is not only unprecedented among the bats that live in the United States,
but among all of the 1,100 plus species of bats and perhaps even among all mammalian
species around the world. A paper came out in the journal Science two
summers ago now in which the authors predicted a 99% chance for regional extinction of little
brown bats– once the most numerous hibernating insect killer bats species in the Northeastern
United States — within about the next 16 years as a result of this disease. So do I think this is a feasible hypothesis?  I would say that it actually is because unlike
other pathogens, say like a virus, that is not as autonomously replicating organism,
or something that’s capable of survival on its own, most fungi are.  Almost all fungi,
including those that are pathogenic, can also live a second type of life phase, whether
just existing as saprobes or decomposers of organic matter in soil. And so a fungus that’s trying to compete with
all of these thousands and thousands of other species for very limited nutrients in soil,
if it has somehow gain the ability to infect the host, which in the case of a bat, maybe
we could just think of a hibernating container of fungus food. In that case, that fungus
gets a huge advantage over its counterparts in the soil and it gains the ability to replicate
and make more of itself, which is effectively the evolutionary goal of a microorganism. So, now if these fungi kill all the bats in
the cave, they just go back to a more quiet reserved lifestyle in the soil and it doesn’t
mater that they drove their host to extinction.  If a virus kills all of its hosts, the virus
goes with them. And so that’s one of our concerns in that
fungi do have this unique ability compared to other pathogens.

So let me talk about
a little bit about the known progression of this disease. The first evidence that we have a White-nose
Syndrome comes from a photograph that was taken by a recreational caver in early 2006. 
The photo which has down, what would that be your right-hand corner of the screen, shows
a bat with this unusual white substance or growth of what we know now as fungus around
its nose. This photo wasn’t actually made widely public
until the year 2008.  What’s interesting is this photograph was taken in a cave, in
east central New York, that is part of a complex of caves that includes a large tourist cave
that entertains about 250,000 human visitors each year. We’ve also since learned that the fungus that
causes White-nose Syndrome is surprisingly wide-spread on bats of Europe, where the bats
seemingly co-exist with it.  In other words, we’ve never, although we’ve seen the fungus
on the bats, we’ve even seen that it can cause White-nose Syndrome in European bats, there’s
no current or historical documentation of these unusual mortality events caused by the
disease in Europe. So, it leads to the plausible hypothesis that
this disease agent may have been introduced to the United States through tourism.  And
that is not an unexpected scenario given the prominent role, and I’ll talk more about this
later, that global travel and trade are known to play in the emergence of infectious diseases
worldwide.

So the next winter, the disease was, let’s say officially discovered, by a
biologist with the New York State Department of Environmental Conservation when they were
conducting routine bat hibernation survey counts for the endangered Indiana bats. 
And by the time they were done doing their surveys, they had found bats with either suspicious
white growth on their bodies or dead bats on cave floors at five sites within two counties
encompassing about a 15-kilometer radius, near Albany, New York. The next winter, my laboratory, others at
the National Wildlife Health Center, our pathology team, our field investigation team, as well
as other diagnostic labs became significantly involved.  So, in another words the people
from New York State, who discovered this the previous spring, had alerted us to this problem. We had some conference calls – we need to
figure out what’s going on; we’re going to be out looking for this; we’re going to be
sending you bats, get ready, it’s going to be ugly. And so, by the time the winter of 2007-2008
was over, we have now identified the disease of 33 sites extending to a circle with a radius
of 210 kilometers from that index site near Albany, New York.  The disease now documented
in New York, Massachusetts, Vermont and Connecticut. The next winter, things got much worse with
the bats with the disease identified now in over a 100 sites extending into nine states
all the way down to the southwestern tip of Virginia, at a distance of over 900 kilometers
from the disease epicenter. And at this point, there’s really no precedent
for studying or responding to a wildlife disease among what we can refer to as cryptic hibernating
animals like bats.  Many of us, if we didn’t for other reasons, know they were there, they’re
just there, people don’t know about them, they’re doing our thing, we’re doing our thing. 
And there’s surprisingly little known about their immune systems and their over-all biology.

So
then the following winter, this will be what, three winters ago now, we worked with Canadian
Wildlife Health Authorities to confirm the disease at several sites in Quebec and Ontario,
showing now that as disease is moving westward across the country, there’s effectively two
fronts for introduction into the mid-western states and on into the western states. At this time we also brought online some new,
more sensitive molecular tests that we can use to find DNA from the fungus which led
to these possible detections of the fungus on bats in Oklahoma and Missouri.  Thankfully,
we’ve not been able to confirm these findings, the surveillance work that we do is opportunistic,
so we don’t have people out all over the place testing every bat they can find. We have people that are doing surveys in caves
in this unobtrusive of a way as possible so as not to disturb the hibernating animals. 
And if they see something suspicious or dead, that animal may be collected and sent to my
lab or other labs for analysis. And so, despite heightened surveillance activity,
we have not yet confirmed these sightings in Missouri and Oklahoma. So this takes us to last winter where we by
the end winter 2010-2011 had confirmed the disease out into 16 states including these
new states of Indiana, Kentucky, North Carolina and Tennessee.  And now in four Canadian
provinces.

Interestingly, we have not yet and this still holds true today, if I pull
up our current map, current as of last Friday, we have not yet seen the high unusual mortality
west of the Appalachian mountains.  And that’s an area that we’re actively investigating. So the question is, we know that this fungus
establishes itself in environments, in the environment, and effectively can become amplified
overtime and the bats then become exposed to more of it earlier each hibernation season. 
So is it just a matter of time and perhaps by the end of March and in the April, as the
bats are completing hibernation for this winter, we’ll see things get much worse in these mid-western
states like Tennessee, Kentucky, Indiana, Ohio, etc., Or, are environmental conditions
different such that the disease never will become as severe west of the Appalachian mountains. So, that’s perhaps one area of the hope but,
the jury is still out on that. In terms of the species affected, we’ve documented
what we in the lab would call clinical disease in six different species of bats that belong
to three different genre.  When all of these bat species – the Little brown bat, the Big
brown bat, the Northern long-eared bat, the Eastern small-footed bat, the Tricolored bat,
which people have previously known as the Eastern Pipistrelle, and the Indiana bat,
which is an endangered species, all have in common, is that these bats all hibernate to
wait out the insect food shortage during the winter time. And so again, we’ll further discuss how
I believe hibernation predisposes these animals to infection by Geomyces destructans– the
fungus.

So with that, let’s transition to a brief discussion of disease ecology. In order to understand emergence and subsequent
spread of the disease, we have to understand how susceptible hosts, pathogens, and environments,
come together in a way that promotes development of the disease.  So, that can be: a stomach
virus outbreak among passengers that are closely housed together on a cruise ship, a cold that
passes through children at day care center, or a White-nose Syndrome outbreak among hibernating
bats in close proximity within an underground hibernation environment like a cave or a mine. So hopefully by now I’ve convinced you that
bats are the host for this disease.  So, I’ll talk more about the pathogen later. 
But let’s talk about this environment, the underground hibernation site. This is an old U.S. Geological Survey map
that show the locations of caves as red dots in the Eastern United States.  And if we
overlay a map showing disease occurrence, the yellow counties on the map, you can see
that it exactly mirrors the cave locations.  So, indicating that these caves provide that
environment that brings the susceptible hosts and the pathogen together. A similar analysis I believe was done when
West Nile Virus was moving westward across the country from its initial point of introduction
on the East Coast.  And effectively if you could find a susceptible bird species like
a crow or a blue bird, a Blue Jay, near a water source that harbored mosquitoes that
harbored the West Nile Virus pathogen, that was your key for early detection of West Nile
Virus in your state as the disease march westward. So to complete this discussion of the disease
triad, we’ve covered the host, we’ve covered the environment: the cool underground dark
cave. Let’s transition to the pathogen aspects of the disease.

So as I mentioned before,
my laboratory and others began to investigate this outbreak in earnest in early 2008, after
we were contacted by the state biologists in New York.  Because of a clinical presentation
of this disease, this white stuff around their faces, we suspected a fungal disease agent. But our early disease investigation efforts
were complicated in that this white material that I show you on the bats’ muzzles — and
it is elsewhere on their bodies too, especially their wings– is very fragile.  And if these
bats are removed from caves it would disappear.  So, by time the bat was shipped to our bio-safe,
bio-secure laboratory in Madison from the East Coast, they didn’t look like anything
was wrong with them, except for they were dead. So an early breakthrough in the investigation
came when a persistent New York state pathologist, Dr. Melissa Behr, who, to our good fortune,
subsequently transferred to the Wisconsin Veterinary Diagnostic Lab, and we’re continuing to
work with Melissa, was also troubled by that observation. She’s getting bats from a mine that was probably
within 10 miles of her lab in Albany and didn’t look like there’s anything wrong with it. 
So, Melissa went in to one of these caves and she collected samples from bats right
on the cave wall of this white material and prepared them for both electron-microscopy
and simple light-microscopy using a blue stain. And what she saw when she scraped this white
material on to her microscope preparations was a pure culture of this unusual fungus
with these hook spores that are actually a spore morphology that never had before been
seen. So, in the meantime at my lab, we were culturing
skin samples from the hundreds of bats that we’re receiving.  And if you take an animal
that lives in a cold, dark cave and culture its skin, you can imagine that it’s just covered
with fungi.  I mean, people probably have been in a musty basement — and musty cave
is the same way– and that musty snow comes from all of the fungi that are present. 
And so how do you figure out which one of those things growing on that bats is what’s
causing your problem.  

Well, one of our breakthroughs and other people were doing
this as well, was we had to ask the question: What do we need to do in the lab to grow something
that’s colonizing the skin of a hibernating bat?  And the skin of a hibernating is about
the temperature of the inside of your refrigerator. And typically, when your doing microbiology
work, you incubate your cultures at the temperature of the human body, like 98.6 degrees, or maybe
at room temperature.  Well, it turns out that for this fungus room temperature is too
warm.  Its upper cutoff for growth is around 65-66 degrees Fahrenheit, around below 20
degrees Centigrade. So, my technician in the lab had put some
of these skin samples on petri plates and stuck it in a laboratory refrigerator.  And
very slowly, this white fungus started to grow on those plates.  And at about the time
that Melissa circulated her photographs of the white scraping right off the bats, our
cultures were starting to grow and we stuck them under microscope and compared them to
Melissa’s photos and found the same fungus. And so, the question is: What is it? It requires cold for growth, and the temperatures
at which it grows unfortunately overlap perfectly with the skin and core body temperatures of
hibernating bats.  The fungus cannot actively grow at warm temperatures, even the temperature
of this room, as I mentioned, would be too warm for it, but that doesn’t mean it would
die.  And so there is a concern about not accidentally transporting it somewhere. The fungus is common on sick bats but absent
from healthy bats and all of the isolates that we have subsequently characterized within
some common genetic marker regions from both North America and now from Europe as well,
are genetically identical.  So when you put this genetic relatedness together with this
radiating pattern of disease spread from a single index site, suggest that, — all this
circumstantial evidences is suggestive, of a single point introduction and subsequent
spread of an introduced pathogen.

So based on DNA sequence analysis of some of these
marker genes, we were able to determine that this fungus belong to a genus of common soil
fungi called Geomyces, which means fungus of the earth.  But based on some of these
other characteristics, its ability to infect bats, its curved spore shape, and its requirement
for growth in cold, we identified it and named is as a new species which we designated destructans,
so the destroying Geomyces. Some work that we’ve recently completed and
published was demonstration according to strict criteria in microbiology known as Koch’s Postulates,
developed by a preeminent microbiology pioneer, Robert Koch, in the late 1800s, that definitively
demonstrate the Geomyces destructans in the absence of other contributing factors is the
pathogen that causes this disease. And so in order to fill Koch’s Postulates,
first you have to demonstrate that the microorganism is found in abundance on all organisms or
all animals suffering from the disease, but absent from healthy animals.  And we accomplished
that through our disease investigation work. Oops!  I jumped one ahead. The microorganism must then be isolated from
the sick animal and grown in pure culture in the laboratory.  And so again we accomplish
that through our disease investigation work. The cultured microorganism should cause disease
when introduce into a healthy animal and then subsequently, you have to be able to re-isolate
the introduced pathogen from the healthy animal.  And so in order to do this, our first challenge
was to develop a system whereby we could successfully maintain wild hibernating bats in our laboratory. 
And so having achieved that, we were then able to conduct the experiment.   

So,
what I’m showing you on this slide, these two images are called histopathology, which
allows us to see how the fungus interacts with tissues from the animal.  And so what
we’re looking at here are cross-sections of bat wing skin and the stuff in dark purple
is fungus. If you think this is– if you recognize this
is bat– and dark color is bad, you’re getting to see the picture. What this fungus does
is it forms these dense aggregations in a way that we haven’t seen with other fungal
skin pathogens of bats.  And it invades and destroys wing tissue, as well as tissue of
the muzzle and elsewhere. And so based on this measure, we were able
to demonstrate that by putting predetermined numbers of spores from this fungus on the
skin of hibernating bats that we were able to cause the disease in 100% of animals that
we treated.  We are also able to transmit the disease from bat to bat by co-housing
sick with healthy bats. Interestingly, when we had bats in separate
cages — hibernating bats in separate cages within our incubators– we did not transmit
the fungal agent between bats by air.  It is an interesting result, but one of my concerns
is that I think that this might stem from the way in which the experiment was done. The bats are kept in mesh cages and the mesh
can obstruct the free movement of spores between cages, as well as, unlike a cave, these incubators
are constantly moving air from within the incubator over the evaporator or chiller coil
and recirculating it back through, so it’s possible that we effectively vacuumed spores
out of the air of the system as it works. And so this still remains an active area of
research. 

Having achieved this objective of demonstrating causality, which is important,
because now we truly can focus disease investigation efforts, as well as disease management efforts
around a single pathogen, and all of those various implications for control and management
strategies. Another important thing that comes out of
this system is our model system for maintaining hibernating bats in the laboratory.  And
this can be used for additional purposes such as consideration for long term maintenance
or holding of captive colonies of endangered bat species to protect them from this disease
to which they might be exposed in the wild until better management solutions are developed. We can also use this system to conduct experiments
to further understand how this fungus kills bats.  And as we develop a better understanding
of how the fungus works and why it’s a pathogen, we can then look for additional ways in which
we could intervene and break this disease cycle. Also, this system could serve as a way for
testing different treatment or management strategies in captivity so that we can test
it in the laboratory on living bats first, before we introduce it into national systems
in the wild and thus avoid unintended adverse consequences. So it’s still leads to the question as to
why would a skin infection like White-nose Syndrome be so deadly to bats. We get athlete’s foot infection, fungal infection
of our feet.  Other animals are susceptible to numerous fungi that for whatever reason
fall in to a category where they call the infection ringworm.  It’s not actually caused
by a worm, it’s caused by a fungus.  But it basically just creates an itchy red spot
on your skin somewhere.  You don’t die from it. All of those other fungal infections are called,
those fungi are called dermatophytes.  And those fungi colonize the layer of dead skin
cells on the surface of our skin.

Geomyces destructans in White-nose Syndrome is different
in that that fungus actually actively invades the skin of bats.  And it penetrates through
that epidermal layer and destroys the epidermis, connective tissues, blood vessels, muscles,
nerve fibers, oil glands, sweat glands — everything that it encounters. Despite the name of the disease, White-nose
Syndrome, perhaps the greatest damage that it causes to the bats is to their wings. 
And these wings are critical to bats not only for them to be able to fly, but they also
perform numerous other physiological functions shown here, including: heat dissipation, water
control; so an intact wing membrane is necessary so the bats don’t lose water while they’re
hibernating and otherwise unable to eat or drink. These wings actually allow the bat, these
large wings, which the skin of the wings accounts for eight times more skin than on the entire
rest of the body of the animal, also passively exchange gases while they’re hibernating. 
When they’re hibernating they’re only breathing a couple times a minute.  And even with their
wings folded in on their bodies it’s been shown that 10% of their CO2 exchange occurs
through theses folded wings membranes. Also, remember theses animals are spending
like six months of their lives hanging upside down.  These wings actually have special
shunts in the blood vessels that help move blood around and function in blood pressure
regulation. So numerous critical physiological functions
all of which are being disrupted by this fungus.   

Let me tell you a little bit about another
project that we did.  Fungal diseases tend to have environmental reservoirs which presents
an additional challenge for managing the disease in the wild.  Even if you could cure the
disease in the infected animals, if they return to their infested hibernation site the next
year they’ll just become re-infected.  So anything that doesn’t give them life-long
immunity and there are questions about whether that’s even possible in a hibernating mammal,
the animals potentially subject to reinfection. And so, we developed the study where we partnered
with biologists as well as recreational cavers from across the eastern United States. And
we were able to collect over 550 soil samples from over 120 caves on states bordering on
in East of the Mississippi River. And the goal was to screen these soil samples
for presence of the fungus. And first our question at this time, not yet knowing whether
the fungus was causing the disease, was to just ask the basic question: Is this fungus
ubiquitous in all of our sites, and the disease is only occurring in the northeast for some
other reason?   Or is that fungus only restricted to areas where we find sick bats? And so, first thing we accomplished through
this work was we were able to culture the viable fungus from samples with hibernating
bats.  And what I’m showing here is just a preliminary work.  We’re continuing to
work with these samples, but this is the first bit that we were able to complete. So these stars show sites from at that time
we were able to both grow the fungus and find its DNA in the soil.  We’re actually able
to find viable fungus in as little as 0.2 grams of soil and so you can see next to a
dime that’s a very small amount of fungus. And if I draw your attention to the picture
down here, most likely, we’re growing the fungus out of soil as a result of these numerous
spores, these are its reproductive structures.  These are environmentally resistant structures
that the fungus produces to satisfy its one goal in life again, which is to make more
of itself.  And so our ability to find it viable in soil highlights the need that people
be very careful — that if they’re going to a site that they don’t accidentally pick up
the fungus, and as a hitchhiker bring it to the next cave that they visit.  

As our
infectivity work showed the bats do transmit the fungus between themselves as they interact,
but this work strongly infers that humans could also be mechanical vectors or transporters
of the fungus.  And so we want to do all that we can so that we don’t also contribute
and make this problem worse. So one of our other interesting findings is
that if you want to screen a lot of samples, using a labor intensive culture method, is
probably not a viable approach.  And so we’ve developed a molecular diagnostic to detect
the fungus in soil. And we tested that on the skin of bats which
do have a lot of fungi on them but fewer varieties of fungi than you would find in soil.  And
when we started applying our PCR test to soil samples, we were finding what we later identified
as cross-reactivity with practically every sample that we analyzed. And so, as an example, these are what some
of the other unknown Geomyces species present in soil from bat caves look like.  

So
the real challenge here is that, on this map, out of just an initial subset of 24 soil samples,
we potentially have identified up to 11 new species of Geomyces.  And all of these are
very very closely related to Geomyces destructans within the mark of genes that we’ve characterized. 
So if you look at this little spot — When you look at this “filegrams,” they’re
called, the closer things are to one another, that the more closely they’re related. These distances have to do with genetic changes. 
So this Clade 10, Clade 11, Clade 12 are relatively distant from Clade 1, which is
Geomyces destructans.  Clade 2, the little spot on the line here, only differs from Clade
1 at four nucleotide positions, out of 624 that we looked at to develop this chart. And so, at this point, we’re really only scratching
a surface of what could very well be one of the most common groups of fungal organisms
in cave soil, this cold damp environment.  And that leads to another important question:
What is so special about Geomyces destructans– that it’s pathogenic to bats whereas all of
these other fungi that presumably bats have co-existed with for millions of years, do
not cause this disease. We’re actually doing some work, some comparative
genomic analysis work, and maybe that will help us to begin to identify virilants determinants
in Geomyces desrtuctans. This slide just shows what some of these guys
look like when we grow them on petri plates.  Here is our type isolate of Geomyces destructans,
here’s an isolate Geomyces destructans cultured directly out of cave soil.  Here are some
of the relatives and you can see they’re kind of similar looking. But interestingly this one that looks like
shag carpeting, genetically, is the most closely related fungus to this one.  So it’s also
interesting how these visual or phenotypic traits don’t seem to necessarily correspond
to genetic relatedness or differences. And here’s a point; I have touched on this
already, but a question that frequently arises is: Where did Geomyces destructans come from
and why did White-nose Syndrome emerge in North America in 2006-2007, approximately? 
So we don’t yet have a definitive answer to this question.  But there’s anecdotal references
in scientific literature to bats with white fungus on their muzzles in Germany, dating
back to the early 1980s. And recent surveillance work in Europe has
indicated that this fungus, Geomyces destructans, genetically and morphologically indistinguishable
for isolates in the United States is widespread as shown in this map, in at least bats in
at least 12 countries. But as I mentioned previously again, these
unusual mortality events, associated with infection in the United States, have not yet
been observed in Europe.  We don’t yet have an answer for that, but it may stem from differences
in environmental conditions that we hope to better characterized, as well as differences
in population levels.

In the northeastern United States, there used to be many very
large aggregations of these bats; thousands, tens of thousands, even hundred of thousands. 
So if you imagine you get a fungus into a colony of 10,000 bats and each of those bats
serves an amplifying host for the fungus, within a very short period of time, one or
two years, there’s great potential for that fungus to make a lot of itself– remember
it’s goal in life– and infect a lot of bats heavily and early in hibernation and cause
heavy mortality. In Europe, as far as people have recorded
back, the bat populations tend to be very much smaller – 10 bats, 30 bats, in some instances
100 bats. And in a couple rare instances, thousands.  But among these smaller populations,
there’s fewer animals– potentially less chance for fungal amplification, less chance for
bat-to-bat interaction and spread lower fungal burdens in the environment, lower infectious
doses; and, whereas these bats get colonized, perhaps the disease just doesn’t progress
to the point where it kills them. People have, most recently, even documented
these lesions that we see on the skin of North American bats that we considered diagnostic
for the disease in European bats.  But again, they’re not dying. Some other work that we’ve done is showing
that if you remove a bat from hibernation or take a bat that’s not yet dead from the
disease and just provide it with a warm environment and food and water, they’ll make a full recovery,
actually remarkably quickly.  They have full capacity to regenerate the skin of their wings
and microscopically, it looks like there was never anything wrong with it. And I think a lot of that just has to do with
turning back on their physiology, their immune system and they can mount a recovery.  And
so effectively in Europe maybe things just never progressed to the degree that we see
them in the United States.  But again, an active area of research.

But still does lead
to that question of: Wow did the disease get here? So this slide depicts civilian global aviation
networks among the 500 largest international airports in 100 countries, most intense air
traffic shown in yellow.  And what this slide shows is that: we humans, have succeeded widely
in breaching historic barriers to the spread of infectious diseases around the world, namely
oceans and mountain ranges. And given our incredible capacity for mobility, there’s
almost no place where we and our hitchhiking pathogens cannot be on this planet, within
just a matter of days –if we set our mind to it. And indeed, global travel and trade are widely
recognized as the most significant drivers in global spread of infectious diseases. So at this point I’ll start to sum up. This
next series slides were developed with a colleague from USDA Wildlife Services, Tom DeLiberto,
who’s a wildlife disease specialist with that agency.  When we think of White-nose syndrome,
it’s not an ordinary disease.  Few diseases have affected as many species, over such a
large geographic area, in such a short period of time, with as much impact on populations. Confounding factors contributing to the severity
of White-nose Syndrome likely include: high density clusters of susceptible individual
animals during hibernation, the time to which they’re uniquely susceptible to this disease,
both high infection and mortality rates, transmission between bats and the environment, and likely
the other direction as well, and environmental persistence.   Even though these animals are hibernating,
they on somewhat regular intervals, like every two weeks or so, they do arouse out of hibernation,
briefly, for maybe an hour at a time, get a drink of water, urinate, various things.
I would just say go to the bathroom, but I don’t think there are bathrooms in these caves. 
So, even though they’re hibernating, there are frequent movements of individuals both
within their clusters, among clusters. And these animals, even though they’re not officially
recognized as migratory, they are known to move distances between summer and fall of
up to 200 miles. And so also the tendency for these, or the
potential ability, for these animals to spread viable spores of this agent over relatively
large distances.  And then couple that with: These animals have a very low and natural
reproductive rate.  These are not flying mice or flying rodents that have many, many
babies.  Bats exhibit very high degree of care for their young and an insectivorous
bat, on average, has one pup per year. And so the potential for these species to
recover is a long-term problem.

These animals are important even though we may not even
see them.  A bat can eat its body rate in insects each night.  Insects consumed by
bats include those that cause vector-born disease, as well as those that impact crop
and forest health. A bat biologist at Boston University estimated
that for the millions of bats that have been estimated to die from White-nose Syndrome,
to date that numbers around 5 million, that would literally amount of to thousands of
tons of insects per year.  And a recent modeling paper estimated that the pesticide, the free
pesticide, or ecosystem services provided by bats, and these a.) Don’t cause us any
money; and b.) Don’t involve any import of potentially toxic chemicals, are value
between $4 to $50 billion per year to the U.S. agricultural industry. So some final thoughts: Why don’t we just
go out and treat these animals with antifungals? Unfortunately, there’s no precedent for using
antifungals or any sort of pharmaceutical compound –short of a vaccine– for treating
disease in free-ranging wildlife.  Especially for a disease with an environmental reservoir,
where the animals are likely to pick it up again from the environments in which they
hibernate. So managing disease in these animals is very
different than strategies that we would use for our pets, for people, or for our farm
animals.  As I said, this environmental reservoir, as well as a very sensitive and unique ecology
in every cave that these bats inhabit, presents unique challenges. And so what I think we’re challenged with
is thinking outside the box to identify practical solutions that can benefit these animals,
that the population level, while first and foremost, not doing any harm to the populations. And so, I’ll conclude here.  This slide acknowledges
numerous people that have worked with me on this problem – graduate students, our pathologists
at the health center, technicians and people from numerous other institutions, as well
as our funding source, funding from U.S. Geological Survey, United States Fish and Wildlife Service,
Bat Conservation International, and others. And I’ll just transition to this last slide
and be happy to take questions. 

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