Bat Disease Threatens Ecological Catastrophe

Published on
by
The Independent/UK

Bat Disease Threatens Ecological Catastrophe

A virulent and deadly pathogen in America is exterminating a predator that is vital to farmers for controlling insect pests

by
Jerome Taylor

A bat showing symptoms of white-nose syndrome. This savage fatality rate threatens to destroy one of North America's top predators, leaving a gaping hole in the continent's food chain with as yet incalculable knock-on ecological effects.

As a biologist with more than four decades of
experience in the field, Thomas Kunz is not prone to over exaggeration.
He likes the data to do the talking. But when it comes to describing the
recent deaths of more than a million bats across the eastern United
States he is unequivocal.

"I've worked with bats over 45 years and never
have I seen, or even known about, any kind of mortality rate comparable
to what we've seen," he says. "The analysis that we've done here
indicates that bats - in at least the north-eastern US - are going to
die out within 20 years."

Dr Kunz, a biology
professor at Boston University and one of a handful of bat specialists
in America, is describing the terrifying advance of white-nose syndrome.
In just four years the virulent fungal infection has spread from a
single cave in upstate New York to massacre more than a million bats
across the North-east.

Scientists and conservationists have been
astonished by both the virulence and viciousness of the disease. When a
cave becomes infected 75 per cent of the bat colony is likely to be
wiped out during the first winter hibernation. After the next winter 90
per cent of the original colony will have succumbed.

This
savage fatality rate threatens to destroy one of North America's top
predators, leaving a gaping hole in the continent's food chain with as
yet incalculable knock-on ecological effects. One senior US wildlife
official has gone so far as to describe the massacre as "the most
precipitous decline of North American wildlife caused by infectious
disease in recorded history".

Jim Dreisacker
doesn't need to read the scientific research to know that bats are
dying. Westchester Wildlife, his family run business in upstate New
York, has been trapping animals for 30 years. Raccoons, skunks,
woodchucks and beavers keep him busy all year round. But each summer the
49-year-old would normally expect a windfall from hundreds of callouts
from homeowners asking him to remove summer colonies of little brown
bats from their roofs and porches.

"The past
two years I don't think we've had a single call," he says. "The little
brown [bat] has just gone. That's a good 20 per cent of my business up
in smoke."

The first outbreak of white-nose was
discovered just 200km north of Mr Dreisacker's home in Howe Caverns, a
popular tourist attraction outside the state capital Albany. In 2006 a
caver reported that many of the bats inside the cave were displaying
white growth on their noses and wings. The infected bats were weaker
than their non-infected cousins, they came out of hibernation too early
and died off rapidly from either starvation or exposure.

By
the following winter white-nose syndrome had spread across upstate New
York. The next year it had reached Vermont, Massachusetts and
Pennsylvania, infecting critical hibernacula (winter hibernation caves)
in the Appalachians. Canada was hit in 2009, with infections in Quebec
and southern Ontario. This year new outbreaks have been reported as far
south as Tennessee, Oklahoma and Missouri. Biologists and pathogen
experts have been scrambling to try to understand how white-nose
syndrome broke out and how it can be stopped or at least reduced.

"One
of the biggest problems we're facing is that we don't really know much
about bats or this fungus," says Hazel Barton, a British born professor
of microbiology at the University of Kentucky whose team are
concentrating on studying the fungus behind the deaths. "But what we do
know is that everything is stacked against bats. It's like this disease
was tailor-made to kill them off in their millions."

How
white-nose syndrome kills is still a matter of scientific inquiry but
the most generally accepted hypothesis is that the fungus attacks the
bats' immune system and interferes with their hibernation patterns.

Throughout
the winter, when food is scarce, many species of North American bats
retreat to hibernacula (the largest ones in the North-east can contain
up to 800,000 bats).

They huddle together in
their tens of thousands, allowing them to save energy by lowering their
body temperature. But this also provides perfect conditions for
transmitting disease.

Throughout hibernation
bats briefly rouse from torpor, the semi-comatose state that allows them
to preserve energy. In most species the arousal rate is once every 12
to 20 days but white-nose infected bats wake up two to three times as
often. The theory is that, just like other fungal infections such as
Athlete's foot, white-nose is uncomfortable and wakes the bats.

"Every
time they arouse it's an enormous drain on their energy levels," says
Dr Kunz, adding that bats have to raise their body temperature every
time they wake. "Energy-wise, one arousal is about the equivalent of 30
days in torpor so when white-nose bats wake early from their hibernation
they are severely undernourished."

Desperate
for food the bats will head to the mouth of the cave in search of
insects. Most of them don't make it and those that do are usually killed
by exposure in a matter of hours.

The results
are horrendous. Colonies have suffered very high death rates with
carcasses littering the floors of caves. Of greatest concern to
conservationists are two critically endangered species that have been
infected, the Grey bat and the Indiana bat. But four other species of
hibernating bat have also been heavily infected.

Yet
the potential extinction of America's bats is more than just a
conservation issue. During spring and summer bats eat more than half
their bodyweight in insects every night to store up fat reserves for the
long winter hibernation. If America's bats die out scientists say the
loss to the farming industry would be devastating.

"Bats
are one of nature's greatest pesticides," says Dr Kunz. "During the 180
days or so that they are out of hibernation, a million little brown
bats will eat - and this is a conservative estimate - in the region of
500 tons of insects. If bats die out farmers will have to use so much
more pesticides."

The University of Boston,
using a test study compiled over eight counties in Texas, believes the
US farming industry will go from spending $1bn (£630m) a year on
pesticides to $9bn.

Places such as Tennessee and
Missouri are now the front line in the bid to stop the fungus from
spreading to the West Coast. The border of the Midwest rests on an
enormous belt of porous limestone and is littered with caves like a
geological Swiss cheese. Beyond that, western states such as California,
Oregon and Washington boast some of the largest bat populations in the
country.

"Fortunately the Great Plains and the
Rockies act as a sort of natural barrier," says Dr Barton. "There's not a
lot of evidence showing that bats from places like Tennessee can fly as
far as the West Coast. Our biggest fear is human transmission."

Just
as small-pox, carried by ships from the Old World, killed millions of
Native Americans, early scientific investigations suggest white-nose
fungus was brought to the US by someone from Europe. It then either
mutated into a virulent and deadly pathogen or already was one for bats
that didn't have the required immunity. A number of bats in Germany,
Hungary and Switzerland have recently been found to carry the white-nose
fungus but are not affected by it suggesting that Europe's bat
population has already experienced a mass fatality and become resistant.

In response the US Government has closed all
caves on public land but all it would take is a careless caver to bring
it out West. "If humans bring it to the West, that would be
catastrophic," says Dr Barton.

The symptoms

A
cluster of hibernating little brown bats showing signs of white-nose
syndrome. The fungus attacks the bat's immune system and interrupts
their hibernation patterns causing them to become severely
undernourished and die. The mortality rate among little browns with
white-nose can exceed 90 per cent in some caves.

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