Friday, April 04, 2014
Wisconsin State officials kept silent on CWD discovery at game farm
http://chronic-wasting-disease.blogspot.com/2014/04/wisconsin-state-officials-kept-silent.html The initial discovery at Wilderness Whitetails was the first in five years. In trying to explain the sudden appearance, McGraw cited several possibilities for transmission, including the chance it occurred spontaneously.
That drew attention of Clausen and wildlife staff at the DNR. Clausen said he knew of no peer-reviewed research showing the disease turned up that way.
Tami Ryan, wildlife health section chief with the DNR, asked the agriculture department to back up the claim.
Richard Bourie, a veterinarian, pointed to a paper by Nobel Laureate Stanley Prusiner of the University of California, San Francisco, who discussed spontaneous occurrence in TSEs.
Ryan wrote back and said, "to the best of our collective knowledge, spontaneous CWD in wild deer has not been substantiated," although she said the DNR wasn't trying to pick a fight.
Friday, April 04, 2014
Wisconsin State officials kept silent on CWD discovery at game farm
http://chronic-wasting-disease.blogspot.com/2014/04/wisconsin-state-officials-kept-silent.html However, a BSE expert said that consumption of infected material is the only known way that cattle get the disease under natural conditons.
“In view of what we know about BSE after almost 20 years experience, contaminated feed has been the source of the epidemic,” said Paul Brown, a scientist retired from the National Institute of Neurological Diseases and Stroke.
BSE is not caused by a microbe. It is caused by the misfolding of the so-called “prion protein” that is a normal constituent of brain and other tissues. If a diseased version of the protein enters the brain somehow, it can slowly cause all the normal versions to become misfolded. It is possible the disease could arise spontaneously, though such an event has never been recorded, Brown said.
http://www.washingtonpost.com/natio...id-safe/2012/04/24/gIQAtelqfT_story.html Conclusion/Significance: Our results point to a possibly higher degree of pathogenicity of BASE than classical BSE in primates and also raise a question about a possible link to one uncommon subset of cases of apparently sporadic CJD. Thus, despite the waning epidemic of classical BSE, the occurrence of atypical strains should temper the urge to relax measures currently in place to protect public health from accidental contamination by BSE-contaminated products.
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003017
http://www.plosone.org/annotation/listThread.action?root=363 http://www.plosone.org/annotation/listThread.action;jsessionid=635CE9094E0EA15D5362B7D7B809448C?root=7143
http://madcowspontaneousnot.blogspot.com/2010/07/spontaneous-generation-of-mammalian.html SPONTANEOUS TSE
Perspectives BIOMEDICINE: A Fresh Look at BSE Bruce Chesebro*
Mad cow disease, or bovine spongiform encephalopathy (BSE), is the cattle form of a family of progressive brain diseases. These diseases include scrapie in sheep, Creutzfeldt-Jakob disease (CJD) in humans, and chronic wasting disease (CWD) in deer and elk. They are also known as either "prion diseases" because of the association of a misfolded cellular prion protein in pathogenesis or "transmissible spongiform encephalopathies" (TSEs) because of the spongelike nature of the damaged brain tissue (1).
The recent discovery of two BSE-infected cows, one in Canada and one in the United States, has dramatically increased concern in North America among meat producers and consumers alike over the extent to which BSE poses a threat to humans as well as to domestic and wild animals. The European BSE epidemic of the late-1980s seems to have been initiated a decade earlier in the United Kingdom by changes in the production of meat and bone meal (MBM) from rendered livestock, which led to contamination of MBM with the BSE infectious agent. Furthermore, the fact that UK farmers fed this rendered MBM to younger animals and that this MBM was distributed to many countries may have contributed to the ensuing BSE epidemic in the United Kingdom and internationally (2).
Despite extensive knowledge about the spread of BSE through contaminated MBM, the source of BSE in Europe remains an unsolved mystery (2). It has been proposed that BSE could be derived from a cross-species infection, perhaps through contamination of MBM by scrapie-infected sheep tissues (see the figure). Alternatively, BSE may have been an endemic disease in cattle that went unnoticed because of its low level of horizontal transmission. Lastly, BSE might have originated by "spontaneous" misfolding of the normal cellular prion protein into the disease-associated abnormal isoform (3), which is postulated to be the infectious agent or "prion."
Five possible sources of BSE in North American cattle. Sheep, deer, and elk could spread prion diseases (TSEs) to cattle through direct animal contact or contamination of pastures. Endemic BSE has not been proven to exist anywhere in the world, but it is difficult to exclude this possibility because of the inefficient spread of BSE infectivity between individual animals (2). BSE caused by spontaneous misfolding of the prion protein has not been proven. CREDIT: KATHARINE SUTLIFF/SCIENCE
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Nevertheless, the idea that BSE might originate due to the spontaneous misfolding of prion proteins has received renewed interest in the wake of reports suggesting the occurrence of atypical BSE (9-11). These results imply that new strains of cattle BSE might have originated separately from the main UK outbreak. Where and how might such strains have originated? Although such rare events cannot be studied directly, any number of sources of the original BSE strain could also explain the discovery of additional BSE strains in cattle (see the figure). However, it would be worrisome if spontaneous BSE were really a valid etiology because such a mechanism would be impossible to prevent--unlike other possible scenarios that could be controlled by large-scale eradication of TSE-positive animals.
Another way to look at this problem is to examine evidence for possible spontaneous TSE disease in other animals besides cattle. Spontaneous BSE would be extremely difficult to detect in cattle, where horizontal spread is minimal. However, in the case of the sheep TSE disease, scrapie, which spreads from ewes to lambs at birth as well as between adults, spontaneous disease should be detectable as new foci of clinical infection. In the early 1950s scrapie was eradicated in both Australia and New Zealand, and the mainland of both these countries has remained scrapie-free ever since. This scrapie-free status is not the result of selection of sheep resistant to scrapie because sheep from New Zealand are as susceptible as their UK counterparts to experimental scrapie infection (12). These experiments of man and nature appear to indicate that spontaneous clinical scrapie does not occur in sheep. Similarly, because CWD is known to spread horizontally, the lack of CWD in the deer or elk of eastern North America but its presence in western regions would also argue against a spontaneous disease mechanism. This is particularly noteworthy in New Zealand, where there are large numbers of deer and elk farms and yet no evidence of spontaneous CWD. If spontaneous scrapie does not occur in sheep or deer, this would suggest that spontaneous forms of BSE and sporadic Creutzfeldt-Jakob disease (sCJD) are unlikely to be found in cattle or humans. The main caveat to this notion is that spontaneous disease may arise in some animal species but not others. In humans, sCJD--which is considered by some researchers to begin by spontaneous misfolding of the prion protein--usually takes more than 50 years to appear. Thus, in animals with a shorter life-span, such as sheep, deer, and cattle, an analogous disease mechanism might not have time to develop.
What can we conclude so far about BSE in North America? Is the BSE detected in two North American cows sporadic or spontaneous or both? "Sporadic" pertains to the rarity of disease occurrence. "Spontaneous" pertains to a possible mechanism of origin of the disease. These are not equivalent terms. The rarity of BSE in North America qualifies it as a sporadic disease, but this low incidence does not provide information about cause. For the two reported North American BSE cases, exposure to contaminated MBM remains the most likely culprit. However, other mechanisms are still possible, including cross-infection by sheep with scrapie or cervids with CWD, horizontal transmission from cattle with endemic BSE, and spontaneous disease in individual cattle. Based on our understanding of other TSEs, the spontaneous mechanism is probably the least likely. Thus, "idiopathic" BSE--that is, BSE of unknown etiology--might be a better term to describe the origin of this malady. ...
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http://www.sciencemag.org/cgi/content/full/sci;305/5692/1918 DR. DEHAVEN: “All right. I think we've got three different questions in there, and I'll try to touch on each one of them.
“First of all, let me correct just a technical issue, and that is you mentioned 1 in 10,000. And actually our surveillance system currently is designed, the one that we have in place now is designed to detect 1 positive in 1 million cattle, and I gave some numbers between 200,000 and 268,000 that would allow us to detect 1 in 10 million as opposed to 1 in 10,000.
“So we would, if we were able to collect in the ballpark of those numbers of samples then we with increasing numbers of samples have an increasingly statistically valid sample from which to determine, one, whether or not the disease exists and, if so, at what prevalence level.
“So our real emphasis is to test as many of those animals as we can, ensure that we get an appropriate geographical distribution, but not setting a specific number as far as a target. Again, consistent with the recommendation from the International Review Team, their recommendation was to test all of them.
“So that's consistent with where we're going is to test as many as we possibly can.
*** “As far as spontaneous cases, that is a very difficult issue. There is no evidence to prove that spontaneous BSE occurs in cattle; but here again it's an issue of proving a negative. We do know that CJD, the human version of the disease, does occur spontaneously in humans at the rate of about 1 in 1 million. We don't have enough data to definitively say that spontaneous cases of BSE in cattle occur or do not occur.
“Again, it's a very difficult situation to prove a negative.
“So a lot of research is ongoing. Certainly if we do come up with any positive samples in the course of this surveillance we will be looking at that question in evaluating those samples but no scientifically hard evidence to confirm or refute whether or not spontaneous cases of BSE occur.
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http://www.usda.gov/wps/portal/!ut/p/_s.7_0_A/7_0_1OB?contentidonly=true&contentid=2004/03/0106.html
http://madcowspontaneousnot.blogspot.com/2010/07/spontaneous-generation-of-mammalian.html tss
