Fact Sheet No. 11 Bovine Spongiform Encephalopathy
By John Maas, DVM, MS Diplomate, ACVN & ACVIM Extension Veterinarian School of Veterinary Medicine University of California-Davis

Introduction

On March 20, 1996 the SEAC committee (Spongiform Encephalopathy Advisory Committee) in Great Britain advised the British government that it (the committee) had become concerned about 10 cases of Creutzfeldt-Jakob Disease (CJD) in humans in the United Kingdom. These cases had occurred over an 18 month period and the basis for their concern were:

• this group of 10 CJD patients were younger than normal, ranging in age from late teens to early 40's,
• the CJD neuropathology in these patients appeared different than that observed in other CJD patients, and
• a review of these patients' medical histories, genetic analysis, and considerations of other possible causes of CJD "failed to explain these cases adequately."

The SEAC concluded there was no direct scientific evidence of a link between Bovine Spongiform Encephalopathy (BSE; mad cow disease) and CJD based on current data; however, in the absence of any known alternative, the "most likely" explanation in their opinion was that these cases are linked to exposure to BSE before the introduction of BSE control measures in 1989.

As cattle producers, we all immediately have a number of questions regarding BSE. This paper will attempt to answer some of these questions.

What is Bovine Spongiform Encephalopathy (BSE)?

BSE is a chronic degenerative disease that affects the central nervous system (brain & spinal cord) of cattle, first diagnosed in Great Britain cattle in 1986. BSE belongs to a family of diseases known as Transmissible Spongiform Encephalopathies (TSEs) that include scrapie (sheep & goats), transmissible mink encephalopathy, feline spongiform encephalopathy (cats), chronic wasting disease of elk and mule deer, BSE (cattle), and kuru, CJD, Fatal Familial Insomnia, Gerstmann-Straussler syndrome (in humans).

Symptoms & Treatments

The clinical signs in cattle appear as nervousness or aggression, abnormal posture, incoordination, weight loss, difficulty rising, progressing to death. There are no treatment or vaccines.

What causes BSE?

The cause of BSE and the other TSEs in other species is not fully understood. Three main theories have been proposed:

• a prion, an abnormal protein capable of causing a cell to produce more abnormal protein;
• a very small unconventional virus, or
• an incomplete virus "virino", lacking a protein coat.

Most of the scientific community feels the cause is a prion or abnormal protein. BSE (like all TSEs) has:

• a long incubation period (months to years),
• is smaller than a typical virus,
• the agent is resistant to sunlight, radiation, and common disinfectants,
• the agent causes no detectable immune response in the host, and
• the agent has not been seen microscopically.

There is currently no evidence that BSE is, in fact, transmissible to humans. Nor is there evidence that naturally occurring diseases of this type (TSEs) are transmitted between species.

How is BSE recognized?

BSE cannot be confirmed in the live animal. There are no tests that can be done on live cattle to confirm the diagnosis of BSE or to identify carrier cattle. It has signs similar to rabies, polioencephalomalacia, Hemophilus somnus infection, and a number of other diseases that affect the brain and spinal cord. The microscopic examination of brain tissue is the only way BSE can currently be diagnosed.

What caused BSE in Great Britain?

The epidemiologic data suggests that BSE was associated with the feeding of meat and bone meal as a protein source to dairy cattle and other cattle. The causative agent is suspected to be from either scrapie-infected sheep or from cattle with a previously unknown TSE. Changes in the rendering practices in the U.K., such as lowering the temperature of processing, potentiated the agent's survival in the meat and bone meal. BSE had never been identified before 1986, when it was first recognized in Britain. BSE has been confirmed in native cattle in Ireland, Northern Ireland, France, Portugal, and Switzerland. BSE has also been identified in cattle exported from Great Britain to Oman, the Falkland Islands, Germany, Denmark, Canada, and Italy. 99% of all BSE cases have been in the U.K.

Do we have BSE in North America?

No. There have been no cases of BSE in the U.S.A. and only one case in Canada, which was in a cow imported to Canada from the U.K. The USDA-APHIS and the USDA-FSIS have had a comprehensive surveillance system for BSE in place since the BSE outbreak in the U.K. was identified. As of March 20, 1996, 2791 brains from cattle have been examined for evidence of BSE in the United States. All were negative.

In addition to this surveillance, many thousands of cattle brains that have been examined by veterinary pathologists in state and university diagnostic laboratories throughout the U.S.A. and Canada in the course of routine diagnostic work on cattle diseases and no BSE has been seen during these examinations. Also, many other species are routinely examined for evidence of these types of diseases.

The USDA has also been active in educational efforts for veterinarians, veterinary diagnosticians, producers, and industry groups with respect to BSE. The USDA also maintains a number of data bases that are used to monitor BSE or other central nervous system diseases that may occur in the U.S.A. Before the ban on British cattle imports into the U.S.A. went into affect in 1989, there were 499 cattle brought from the U.K. to the U.S.A., these cattle were followed until they died (113 are still alive and show no evidence of BSE). In July of 1989 the USDA banned importation of all cattle from countries in which BSE had occurred.

Have we imported beef or beef products from the U.K.?

No beef or beef products have been imported into the U.S.A. since 1989 from the U.K. Also, prior to 1989, there were no FSIS approved establishments eligible to ship U.K. beef to the United States; therefore, no beef was imported prior to the 1989 ban. Imports of ruminant products from the U.K. and other BSE affected countries has been further restricted since 1989. For example, fetal bovine serum used in research can not be imported from BSE countries. Prior to 1986, a small amount (14 tons) of ruminant protein (rendered products) was imported from the U.K. to the United States. Our current regulations prohibit the importation of ruminant proteins from all countries affected by BSE.

What is Creutzfeld-Jakob Disease (CJD)?

CJD is a slow degenerative disease of humans that affects the central nervous system, causing dysfunction, progressive dementia, vacuolar degeneration of the brain, and death. CJD occurs throughout the world at a rate of about 1-2 cases per million people per year. We have CJD in the United States and the incidence is also about 1 case per million per year. The rate of CJD in the U.K. is the same as in the U.S.A. Also, the rate of CJD cases in Australia and New Zealand where neither BSE or scrapie (sheep) has been reported, is also about 1 case per million people per year. Also, U.S. farmers or veterinarians are not at any higher risk of CJD than the general population. Additionally, scrapie has existed in the U.K. sheep population for 200 years and has never been shown to be a human health risk.

Where do we go from here?

Between 1986 and now, over 160,000 head of British cattle have been killed from over 32,000 herds known to have been affected with BSE. Recently, the European Union and Great Britain have reached an agreement to begin to kill 15,000 cattle per week in Great Britain to eliminate this disease. The feeding of ruminant-derived protein to cattle and other ruminants has been banned in the U.K.

In the U.S.A., an extensive surveillance program has been in place for some time and that effort will be increased in the future. Currently there is no known risk to the cattle population of the U.S.A., nor is there is any known risk to people consuming beef products. Research into the cause of BSE is needed, as well as methods to identify, control, and eliminate this problem. Obviously, this problem has decimated the cattle industries of Great Britain and we must not allow this disease to become a problem in the United States. This disease illustrates how important research of cattle diseases is to the health of the industry and to public health and confidence.