Studying white nose disease in bats - Veterinary Practice
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InFocus

Studying white nose disease in bats

JOHN BONNER
reports on a number of the discussions at the latest meeting of the Veterinary Association for Wildlife Management

CONSERVATIONISTS are
carrying out a study on Britain’s
bats to find out if they could
succumb to a disease which
threatens to wipe out many North
American species.

White nose disease has killed an
estimated 5.7 million insectivorous
bats in 20 US states and four Canadian
provinces, Alex Barlow of the Animal
Health and Veterinary Laboratories
Agency, Langford, told the Veterinary
Association for Wildlife Management
(VAWM) at its November meeting in
London.

The condition is known
to affect nine species – and
with mortality rates
approaching 100%, some of
these species could
potentially become extinct.
“This is the most
catastrophic decline in any North
American wildlife species due to an
infectious disease ever recorded,” he
said.

The first reported incident was in
bats hibernating in the Schoharie cave
system in New York State in January
2007 and the condition spread rapidly
throughout the adjoining north-eastern
states.

Cavers and wildlife biologists have
found large numbers of dead bats in
the winter hibernation period. They
have also seen abnormal behaviour in
living animals such as winter daytime
flights and bats roosting near the entrances of caves, where they will
experience dangerous fluctuations in
temperature and humidity.

Surviving bats could often be seen
with white patches around the nares
which has been identified as the
fungus Geomyces destructans. Post-
mortem examination on dead bats
showed the fungus in the skin and hair
follicles over much of the bat’s body,
particularly the wings.

There is surprisingly little evidence
of any inflammatory response to the
fungal growth. During hibernation the
bat’s body temperature and general metabolism are reduced and so it is
unable to mount an effective immune
response, he explained.

Mr Barlow suggested that the
fungus acts like a wick in drawing
moisture away from the bat’s body and
so it quickly becomes dehydrated.
Affected animals wake from their
torpor and go off in search of water
but warming the body to enable it to
fly is a massive drain on the creature’s
energy stores and even those that
survive may become severely
emaciated by the end of the
hibernation period.

It is significant that the reported mortalities are higher in smaller bat
species like the little brown bat (Myotis
lucifugus
) with a proportionately larger
surface area. However, it is those
species that are small in numbers as
well as size and have a limited
geographical range such as the Indiana
bat (M. sodalis) that are a particular
cause for concern, he said.

If some bat species do go extinct
in North America then there may be
serious knock-on effects for the rest of
the ecosystem. Mr Barlow pointed out
that during its active months a bat may
eat up to 3,000 small insects every
night.

Favourite prey includes some of
the midge species that are responsible
for the spread of important zoonotic
conditions like West Nile fever and
major economic threats such as
bluetongue virus. If farmers are forced
to control insects with heavier use of
pesticides, then that could have
implications for other, more welcome
insect species.

Where did it originate?

So where did the disease come from?
Anecdotal evidence from a caver
suggests that there may have been
unexplained mortalities in bats in the
Howey cave system, also in New York
State, a year before the problem
became apparent to wildlife biologists.

That is a major tourist attraction
receiving 250,000 visitors a year from
all over the worlds.

Genetic analysis of the fungus
suggests that a single clone is
responsible for the epidemic. Other
studies also appear to have pinpointed
the source as being from somewhere
in continental Europe.

So far the pathogen has been
isolated in bat colonies from 18
European countries but it does not
appear to cause any significant
outbreaks of disease and so the fungus
has co-existed peacefully with
European bats for some time.

It is not clear if bats in Britain are
unaffected by the fungus like their
European cousins or may be
potentially vulnerable to the same sort
of epidemics seen across the Atlantic.
A few dead bats have been recovered
from caves in the UK but analysis of
fungal growths on their bodies has
suggested that these were saprophytic
species that colonised the bats’ bodies
after they had died.

So this winter the AHVLA and
volunteers from the Bat Conservation
Council have been taking samples
from hundreds of sites around the
country, focusing particularly on the
south-east counties which can be
reached by migrating bats arriving
from Europe.

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