- PARIS (AFP) -- Brain-destroying
prion disease can spread among deer through faeces shed by animals which
have been infected by the deadly pathogen but are not sick, a study published
on Wednesday suggests.
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- The paper implies that the mysterious disorders known
as chronic wasting disease (CWD) and scrapie -- cousins of mad-cow disease
-- could be transmitted in a hitherto-overlooked way, posing a headache
for farmers.
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- The scientists are led by University of California neurologist
Stanley Prusiner, who won the 1997 Nobel Medicine Prize for research into
prions, the rogue proteins blamed for turning brains spongey.
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- Prion diseases are well-researched disorders in deer
(CWD), cattle (bovine spongiform encephalopathy, or BSE), sheep and goats
(scrapie), cats (feline spongiform encephalopathy, FSE) and in humans (Creutzfeldt-Jakob
disease, CJD).
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- Many aspects about them are unclear, though. In deer,
CWD is known to be handed on from mother to offspring, but other paths
of infection are deemed possible.
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- Publishing in the British journal Nature, Prusiner's
team probe a theory that deer may pass on the prion in their faeces, thus
creating a risk that other deer will pick up the pathogen in the soil when
they graze.
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- Over the course of months, the investigators collected
the faeces of five mule deer (Odocoileus hemionus) and then orally infected
them with CWD prions.
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- They continued taking samples until the animals died
or developed signs of the disease and were euthanised.
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- Faecal samples -- irradiated to kill germs and viruses
but leave the prions untouched -- were injected into the brains of genetically
modified mice.
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- Samples that had been collected before the deer were
infected and three to four months after infection had no effect.
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- But 14 out of 15 samples that were collected after the
four-month mark caused the mice to fall sick with CWD-like symptoms.
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- The results, say the authors, point to a "horizontal"
way by which CWD could spread among deer in the wild -- and, possibly,
by which scrapie could spread among sheep and goats.
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- The "faecal-oral route" was given credence
by a 1994 Icelandic study in which sheep with scrapie were held in a field,
removed and then replaced with scrapie-free sheep, which then went on to
develop the disease.
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- But an unresolved question is whether prions can survive
long enough in the soil to infect other animals. Past studies have sent
back conflicting data on this; some say harsh weather and microbial enzymes
in the soil degrade the pathogen.
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- The new paper did not touch on BSE. That disease, which
erupted in Britain in the 1980s, unleashed a scare in 1996 when BSE-infected
beef was linked to a rare form of fatal neurodegenerative disorder in humans,
variant CJD.
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- The causes of BSE have been fiercely debated. One idea
is that herds became infected by eating the ground-up carcasses of scrapie-infected
sheep.
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- BSE has been fought through a culling of animals and
a change of feeding practices. Several studies into cattle suggest there
is no "faecal-oral route" for BSE.
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- Patricia A. Doyle DVM, PhD Bus Admin, Tropical Agricultural
Economics Univ of West Indies Please visit my "Emerging Diseases"
message board at: http://www.emergingdisease.org/phpbb/index.php Also
my new website: http://drpdoyle.tripod.com/ Zhan le Devlesa tai
sastimasa Go with God and in Good Health
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