- Meat from deer infected with chronic
wasting disease (CWD) has been shown to transmit the prion disease to genetically
altered mice, according to a report published Jan 26 in Sciencexpress,
part of Science magazine.
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- The experimental findings "raise
the possibility that dietary exposure to prions might occur through meat
consumption," writes researcher Glenn Telling at the University of
Kentucky, along with six other colleagues.
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- CWD, a rare brain-wasting disease that
affects deer, elk, and moose in parts of North America, is similar to bovine
spongiform encephalopathy (BSE), or mad cow disease. It has not been known
to infect humans, and the skeletal muscle meat from deer and elk was not
previously believed to contain infective levels of abnormal prion protein.
However, state game agencies now advise hunters to take precautions when
handling carcasses, and some states test harvested animals for CWD.
-
- "The emergence of CWD in an increasingly
wide geographic area and the interspecies transmission of bovine spongiform
encephalopathy (BSE) to humans as variant Creutzfeldt Jakob disease (vCJD)
have raised concerns about zoonotic transmission of CWD," Telling
and colleagues write.
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- "We don't know if people will develop
a human prion disease as a result of exposure to CWD but we know people
developed prion disease as result of exposure to BSE," Telling said
in a Reuters news service story Jan 27. "Obviously the most likely
route of exposure would be via meat, and that is why we addressed this."
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- "It's difficult to predict how prions
will behave when they cross species barriers," Telling told Reuters.
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- To test the infectivity of skeletal muscle,
the researchers used specially adapted mice that expressed cervid prion
protein (CerPrP), which made them susceptible to CWD. Groups of these mice
were inoculated intracerebrally with extracts of leg muscle from either
CWD-infected or CWD-free mule deer, while other mice were inoculated with
central nervous system (CNS) materials from both infected and uninfected
deer.
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- The researchers found that all skeletal
muscle samples from infected deer led to the progressive mental dysfunction
associated with transmissible spongiform encephalopathies (TSEs), with
mean incubation times ranging from 360 to roughly 490 days. The incubation
period after infection with CNS material was shorter, from about 230 to
280 days.
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- The skeletal muscle and brain tissue
from uninfected deer didn't cause disease in the special mice.
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- The researchers note that similar studies
involving skeletal muscle from BSE-infected cattle failed to show such
high levels of prion infectivity. The study also shows that prion levels
were lower in muscle than in the CNS and that the muscle prion levels may
vary. Studies to assess the prion titers are under way, the authors write.
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- The report says the risk of CWD infection
following consumption is reduced by relatively inefficient prion transmission,
but that the findings show the muscle tissue most likely to be consumed
by humans is a significant source of prion infectivity.
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- "Humans consuming or handling meat
from CWD-infected deer are therefore at risk to prion exposure," the
report concludes.
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- Both the findings and the methodology
of the study are significant, said Srinand Sreevatsan, DVM, MPH, PhD, an
associate professor in the University of Minnesota's Department of Veterinary
Population Medicine.
-
- The presence and infectivity of CWD prion
in muscle hasn't been demonstrated with a bioassay before, Sreevatsan told
CIDRAP News. The bioassay allows researchers to know if the misfolded prions
are present and if they are capable of causing the disease in an animal
model. "It's only now that we are realizing the sensitive assays we
can use."
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- "The presence of infectivity in
the muscle tissue in CWD does raise some issues. That it's there and it
is infectious is a concern," he said, but added that it is important
to do a risk assessment as well. "Is it present in enough quantity
to be of public health significance? We don't know. That needs to be determined."
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- "It may not be in sufficient quantities
to cause infection [if people consume it]," he added.
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- Telling G, Angers R, Browning S, et al.
Prions in skeletal muscles of deer with chronic wasting disease. Sciencexpress
2006 Jan 26 (early online publication) [Abstract]
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- First published January 31, 2006
- See also:
- Oct 26, 2005, CIDRAP News story "Chronic
wasting disease found in moose"
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- Institute of Food Technologists scientific
summary report "Transmissible Spongiform Encephalopathies," published
Jun 2005
-
-
- 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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