By Lauran Neergaard AP Medical Writer
Washington (AP) – Deer probably spread the brain-destroying
illness chronic wasting disease through their saliva, concludes a
study that finally pins down a long-suspected culprit.
The key was that Colorado researchers tested some special
Chronic wasting disease is in the same family of fatal brain
illnesses as mad cow disease and its human equivalent. There is no
evidence that people ever have caught chronic wasting disease from
infected deer or elk.
But CWD is unusual because, unlike its very hard-to-spread
relatives, it seems to spread fairly easily from animal to
Scientists were not sure how, primarily because studying large
wild animals is a logistical nightmare. The sheer stress of
researchers handling a deer caught in the wild could kill it.
Likewise, animals deliberately exposed to infections must be
kept indoors so as not to spread disease, another stress for deer
used to roaming.
So Colorado State University researcher Edward Hoover turned to
fawns hand-raised indoors in Georgia, which has not experienced
chronic wasting disease.
‘This allows you to do this safely so the deer aren’t freaking
out,’ explained Hoover, who reported the first evidence of saliva’s
long-suspected role in Friday’s edition of the journal Science.
‘These deer are calm and approachable.’
Hoover took saliva from wild Colorado deer found dying of CWD,
and squirted it into the mouths of three of the healthy tame deer –
about 3 tablespoons worth.
Additional tame deer were exposed to blood, urine, and feces
from CWD-infected deer.
He housed the newly exposed deer in a specialized lab for up to
18 months, periodically checking tonsil tissue for signs of
infection and eventually autopsying their brains.
All of the saliva-exposed deer got sick.
So did deer given a single transfusion of blood from a
CWD-infected deer – not a surprise, as blood is known to transmit
this disease’s cousins. But it does reinforce existing warnings to
hunters in states where CWD has been found to take precautions in
handling their kills.
The three deer exposed to urine and feces didn’t get sick. That
doesn’t rule out those substances, Hoover cautioned; he simply may
not have tested enough animals.
Proving that saliva is able to spread CWD is important, so that
scientists next can determine exactly how that happens in the wild,
said Richard T. Johnson, a Johns Hopkins University neurology
professor who headed a major report on prion science.
‘You can move deer out of a pasture, put other deer into the
pasture, and they’ll come down with the disease. It’s not even
casual contact, it’s contact with the pasture,’ Johnson said. ‘It
must be something in their secretions.’
Is it spread through shared salt licks? Or by drooling onto
grass or into streams? Studying environmental contamination by
infectious proteins, called prions, that cause CWD is among
Hoover’s next steps.
‘It’s very likely they could be shedding a lot of saliva’
shortly before death, noted Richard Race, a veterinarian who
studies CWD at the National Institutes of Health’s Rocky Mountain
Laboratories. ‘Saliva’s a good bet.’