falls apart,” Hicks says. Any disturbance
will make it visually disappear. But it’s
not truly gone.
Smooth white patches may also form
on the ears, tail, feet or wings, which
recent work shows are most vulnerable.
Researchers are now coming to realize
that a more apt name for this epidemic
might be wing-digesting
syndrome.
This fungus doesn’t
invade blood vessels and
spread the way other fungal species do, explains
wildlife pathologist Carol
Meteyer, also of the USGS
health center in Madison.
G. destructans initially
starts multiplying on the
skin of wings, then shoots
hyphae — essentially the
body of the fungus — out
in all directions, she,
Blehert and colleagues reported last year
in BMC Biology.
“My assumption is these hyphae are
releasing biologically active enzymes
because they digest the skin,” Meteyer
says. Instead of creating open, oozing
sores, the fungi fill in behind the eroding
skin. What’s left is a wing with fungal cells
increasingly substituting for bat cells.
With a bat’s immunity depressed during hibernation, white-nose syndrome
doesn’t elicit redness, swelling or irritation. Only when an animal wakes and its
body temperature increases can it begin
to fight the fungus. By then it’s usually
too late.
Though most bats wake periodically
throughout the winter, bats infected
with white-nose may rouse more often
and for a longer time than noninfected
bats. Researchers at USGS’s Madison
center note that frequent and somewhat
prolonged arousals by infected bats also
tend to coincide with emaciation and
attempts by the animals to slake their
thirst. The team now suspects that fungal digestion of wing tissue underlies
both symptoms.
Wings make up about 85 percent of
the total skin surface of a bat’s body,
Blehert notes. Skin on the wing not only
plays a role in blood pressure regulation
and gas exchange, he says, but also water
balance. As wing infections progress, a
developing thirst is likely to rouse bats.
Waking pushes body temperature up to
normal and puts a big drain on a bat’s
stores of energy — fat.
Not surprisingly, awake, infected bats
tend to be weak and
hungry. McAlpine
says some bats at the
infected cave he vis-
ited were so famished
that they left in search
of food. But because it
was still March, there
were no insects to
eat. “These bats were
essentially dead on
the wing,” he says. He
encountered several
that traveled too far in
their fruitless search
for food; they froze to death.
To evaluate white-nose’s effects on
rousing under controlled conditions,
Craig Willis of the University of Winni-
peg in Manitoba and his colleagues have
monitored a colony of several dozen
infected little brown bats in the lab. His
team installed sensors to keep track of
the animals’ body temperatures and
video cameras to record when animals
rouse, and whether they show signs of
excessive thirst. The team is now analyz-
ing the video footage to get a better sense
of the devastating chain of events that
the fungus appears to trigger.
Despite the damaging effect in American bat colonies, G. destructans–infected
European bats aren’t dying, an international team of scientists reported April 27
In white-nose syndrome,
a bat’s normally healthy
wing tissue (top band) gets
replaced by dark and bubbly
fungal cells (bottom band).
in PLoS ONE. Jeff Foster of Northern
Arizona University in Flagstaff and
others are now investigating why.
Foster is sequencing the genome of
G. destructans from seven sites in the
United States and Canada and four in
Europe. Although fungi from the two
continents are relatively closely related,
preliminary findings show that there is
far less variation in genes within the
North American samples. That find
is precisely what he would expect if
the American samples derive from a
common immigrant that had been
established elsewhere for a long
time — such as in Europe.
Last year, researchers at the Broad
Institute in Cambridge, Mass., completed
a more thorough analysis of the U. S. variant’s genome. This July, they finished cataloging the individual genes contained in
the fungal DNA and predicted what proteins the genes make, says team leader
Christina Cuomo. Over the coming year,
her group will compare these proteins
with those produced by different fungal
species (her team has already sequenced
genomes for more than 50 fungi, none of
which affect bats). Any proteins unique
to G. destructans could shed light on how
the pathogen kills, Cuomo says, and how
it might be killed.
But Willis isn’t waiting. This past winter his group began directly investigating
the relative toxicity of G. destructans from
each continent in Canadian bats collected
from a syndrome-free cave. The researchers infected 18 bats with the American
strain, 18 more with its European cousin
and left a third batch untreated. If each
fungal variant causes comparable disease,
then some special vulnerability of North
European bats appear resistant to white-nose syndrome, a clue that may help fight
the spread of the fungus that causes it. A European bat with signs of the fungus
(left) was able — with a little grooming— to clear the infection in nine days (right).
