MAD COW NEWS

Missouri Stockgrowers' Association
December 24, 2003


On Thursday, December 11, 2003, R-CALF-USA and a number of its affiliate cattle organizations sponsored a Prion Disease Roundtable in Denver, Colorado. Dr. R. M. Thornsberry, President of the Missouri Stockgrower’s Association was commissioned by R-CALF President Leo McDonnell to organize the roundtable and invite prion specialists to present information at the roundtable that would benefit the education of livestock producers throughout the United States.

Dr. Stanley Prusiner, the scientist who discovered prions, for which he won the Nobel Prize in medicine, was invited to the roundtable. Notes from Dr. Prusiner’s presentation on prions and prion diseases was presented to the roundtable by Dr. Thornsberry, who had attended one of Dr. Prusiner’s lectures on prion diseases. Although uable to attend the roundtable, Dr. Prusiner provided the roundtable with five papers published in prestigious peer reviewed medical and science journals. These papers were provided to all the attendees and key points from these papers were discussed at the beginning of the roundtable discussion. Dr. Prusiner emphasized normal cooking temperatures do not inactivate prions. This point is especially important when humans are exposed to Bovine Spongiform Encephalopathy (BSE) prions in the normal process of consuming beef muscle cuts that may contain significant nerve tissue. Dr. Pruisner’s laboratory is currently developing a live animal test to determine whether or not an animal is carrying BSE prions prior to entering the food chain for human consumption.

Dr. Jason Bartz, an applied science researcher from Creighton University, Omaha, Nebraska, was the second presenter at the roundtable. Dr. Bartz presented current research data on prion diseases and particularly outlined the pathogenesis of prion diseases. Dr. Bartz presented data that defined the ability of prions to replicate in secondary lymphoreticular system tissues, and the ability of prions to travel throughout the nervous system, finally locating within the brain or brain stem tissues where pathological changes occur. Dr. Bartz also presented data to illustrate the severity of prion disease appears to increase as the disease is passed from animal to animal. Dr. Bartz presented data to illustrate the infectivity and persistency of prions. Prions in brain tissue were heated to 600 degrees Celsius--that is over 1200 degrees Fahrenheit--and injected into brain tissue. These heat treated prions were still capable of causing prion disease changes. In other words, there is no commonly utilized method with which to inactivate prions on surgical instruments, surfaces, pens, corrals, chutes, ground, etc. Dr. Bartz also presented data that indicates tongue lesions or sores provide the mechanism for prions to enter brain tissue through the nerve that supplies the muscle tissue of an animal’s tongue. Dr. Bartz, with more sensitive immunodection, has identified prions in muscle tissues of the tongue.

Dr. Terry Spraker, a veterinary pathologist from Colorado State University, demonstrated in his presentation that not all animals that develop prion disease die immediately. On the contrary, animals can carry prion disease and shed large numbers of prions for months and maybe years before the disease progresses to the point where it may be identified by clinical symptoms. Dr. Spraker mentioned that research being done by Hamair Amair in Ames, Iown, Mike Miller with the Colorado Department of Wildlife, and Beth Williams thus far shows no evidence of natural transmission of Chronic Wasting Disease in deer and elk to cattle.

Dr. Linda Detwiler, adjunct professor and animal health consultant specializing in prion diseases and other regulatory issues, presented her findings from prion disease investigations in Canada and Europe. Dr. Detwiler also presented a short video of four Holstein cows with mad cow disease (BSE). The clinical signs were extremely subtle. Although they appeared essentially normal, they could have infectivity in certain tissues such as intestine and tonsil for months prior to developing clinical signs. Dr. Detwiler identified risk factors present in the United States and Canada that could result in exposing negative ruminants to prions. The BSE case in a native Canadian cow demonstrates that the BSE agent is in North America. Some of the current practices which could pose a risk to the North American cattle production system include no specified risk material (SRM) ban (tissues such bovine brain and spinal cord can still be included in nonruminant feed) so if the agent is present there could be contamination of feed for ruminants if produced in plants with no dedicated lines. There are certain exemptions to the current US feed ban which could potentially expose US cattle to the BSE agent. These include the feeding of ruminant blood meal, unfiltered beef tallow, and poultry litter to ruminants. In addition, there is no SRM ban in place for public health. That is, bovine brain, spinal cord and other potentially infected tissues may still be used in food products.

Dr. Susan Keller, Deputy State Veterinarian for North Dakota, presented the regulatory issues surrounding prion diseases including Scrapie in sheep and BSE in cattle. During a discussion on the most recent Havard Risk Assessment for BSE in the United States, Dr. Keller attempted to determine what the industry response would be to a single case of BSE in the United States. The fact that the incubation period of BSE is extremely long (possibly up to 20 years), Dr. Keller determined that responding to a single case of BSE could potentially encompass up to 20 years of regulatory activity to ensure the public that BSE was under control in the United States. Although the Havard Risk Assessment for BSE is accurate, it does not take into account the devastating effect of a single case in the United States on state regulatory function and financing. Once Canada is designated an acceptable risk country for export of meat or animals into the United States, other countries with a history of cases of BSE will also petition the United States government for the same export status.

Following the roundtable, a general consensus was reached on four topics:

-- Prion diseases are infective, especially within susceptible species. Although most animals that exhibit symptoms of prion disease die, thus ending the progression of the disease, that animal may in fact shed many prions into the environment prior to and after death.
-- Since there is no known Standard Operating Procedural method to adequately disinfect or inactivate prions, extreme caution should be taken with prion diseases, their research, and their disposal.
-- New more sensitive prion histochemial testing procedures identify prions in muscle tissue as well as lympoid and nervous tissue. This finding is reinforced by Dr. Prusiner’s laboratory, which is developing a preslaughter test to identify prions in tissues prior to meat entering the food chain. This finding means human exposure to prions in certain muscle cuts of beef is possible.
-- Opening the border to Canada is questionable until high risk factors such as the feeding of blood meal, feather meal, unfiltered beef tallow, poultry manure, and non-ruminant species feeding of meat and bone meal is properly addressed by the United States Department of Agriculture and the Food and Drug Administration.

The roundtable presentations and discussions were recorded. A transcript will be made available to the Academy of Veterinary Consultants, the American Association of Bovine Practioners, and the Colleges of Veterinary Medicine throughout the United States and Canada. A condensed version translated for the livestock industry will be made available to educate livestock producers about prion related diseases.

This press release was written by Dr. R. M. Thornsberry, the moderator of the Prion Disease Roundtable and has been edited and approved by those participating in the roundtable. A transcript approved by and edited by all participants will be available in January, 2004. For a copy of that transcript, write to: R. M. Thornsberry, D.V.M., P.O. Box 818, Richland, MO 65556 or email:cowman@webound.com