NEWSLETTER ARTICLES
Livestock and Natural Resources

Bovine Spongiform Encephalopathy (BSE), or what the news media usually insists on calling "mad cow disease," has now been recognized for 10 years as an emerging disease of cattle. There are still many questions regarding this disease. However, there has been progress, and much more is known about the mysterious condition.

What is Bovine Spongiform Encephalopathy (BSE)?

BSE is a chronic degenerative disease that affects the central nervous system (brain and spinal cord) of cattle. It was first diagnosed in cattle in Great Britain in 1986. The clinical signs or symptoms in cattle appear as nervousness or aggression, abnormal posture, incoordination, weight loss, difficulty rising, progressing to death. There is no treatment for these conditions, and currently there are no vaccines available for prevention.

BSE belongs to a family of diseases known as Transmissible Spongiform Encephalopathies (TSEs). These TSEs include scrapie (sheep and goats), transmissible mink encephalopathy, feline spongiform encephalopathy (cats), chronic wasting disease of elk and mule deer, and BSE in cattle. Humans have a number of TSEs also. These include kuru, Creutzfeld-Jakob Disease (CJD), Fatal Familial Insomnia, Gerstmann-Straussler Syndrome (in humans).

How is BSE recognized or diagnosed?

BSE cannot be confirmed in the live animal. The microscopic examination of brain tissue is the only way BSE can currently be diagnosed.

What causes BSE?

The cause of BSE and other TSEs in other species is not fully understood. Most of the scientific community feels the cause is a prion or abnormal protein. BSE, like all TSEs, has: (1) a long incubation period (months to years); (2) is smaller than a typical virus; (3) the agent is resistant to sunlight, radiation, and common disinfectants, and (4) the agent causes no detectable immune response in the host.

Why did BSE occur in Great Britain?

The bottom line to this question is "no one knows for sure." 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 have come from either scrapie-infected sheep or from cattle with a previously unknown TSE. Changes in the rendering practices in the United Kingdom (UK), such as lowering the temperature of processing, may have allowed the survival of the agent 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. It is now thought that meat and bone meal exported from the UK was responsible for the infection of native cattle in other countries. BSE has been identified in cattle exported from Britain to other countries.

Prior to 1986, a small amount (14 tons) of ruminant protein (rendered products) was imported from the UK to the US. Our current regulations prohibit the import of ruminant proteins from all countries affected with BSE. Worldwide, 99% of the BSE cases have occurred in the UK. Currently, the BSE epidemic in Britain is winding down as the control measures are successfully taking effect. However, the epidemic has been devastating to the dairy and cattle industries in the UK.

Do we have BSE in the United States?

No! There have been no cases of BSE in the US. There was one case in Canada (in a cow imported from Great Britain). Before the ban on British cattle imports into the US went into effect in 1989, there were 499 cattle brought to the US from Britain. All of those cattle were carefully accounted for and none showed evidence of BSE. Of these 499 cattle, 11 are still alive and are being monitored carefully. They are in Alabama and Pennsylvania and are under close surveillance.

Veterinarians and others in the US are continuing very aggressive surveillance programs for BSE. This includes the National Veterinary Services Laboratory in Ames, Iowa, the Centers of Disease Control, the USDA, and all state veterinary diagnostic laboratories. Surveillance of high risk populations, such as disabled dairy cattle, has continued at a high rate, with more than 1,000 cattle from California alone examined for evidence of BSE to date. So far, there has been no evidence of BSE in the USA.

What else has been done to prevent BSE from occurring in the US?

No beef or beef products, including items such as fetal bovine serum used in research laboratories, have been imported from Britain since 1989. Also, no beef products were imported from Britain to the US prior to 1989 because no FSIS-approved establishments for export to the US existed in the UK. Current regulations prohibit the importation of ruminant protein from all countries affected with BSE. As mentioned above, surveillance is continuing at a very high rate.

What is Creutzfeld-Jakob Disease (CJD)?

CJD is a slow, progressive disease of humans that affects the central nervous system, causing dysfunction, progressive dementia, and death. CJD occurs throughout the world at a rate of about 1-2 cases per million population per year. There has been a major change in CJD in Britain since the outbreak of BSE in cattle. This change has been the recognition of a new variant CJD or nvCJD in humans. To date, there have been 35 cases of nvCJD recognized in humans in Britain and one case in France. The exact cause of this new form of the disease is not entirely known. However, the evidence suggests that BSE is involved. This is probably occurring through the eating of “infected” meat prior to the recognition of the BSE epidemic in cattle. The abnormal protein in the brain of nvCJD patients and the abnormal protein in the brain of BSE cattle is very closely related and, perhaps, more closely related than the proteins identified in other TSEs. While the exact relationship between BSE and nvCJD is not fully understood, the prudent course has been to assume a link between the two and work to eliminate BSE in Europe and prevent BSE from occurring in the US.

What is currently being done to prevent BSE in the US?

In addition to importation bans on cattle and ruminant protein sources from countries with BSE, surveillance in the US continues at a very high rate. Also, in 1997, the FDA enacted a ruminant feed ban here in the US. This prohibits feeding protein derived from mammals (such as meat and bone meal) to be fed to ruminants. There are some exceptions to this rule, but in general it is very strict and would certainly help limit any outbreak, should one occur.

We have some TSEs that occur in the US. These include such diseases as scrapie in sheep, chronic wasting disease in elk and deer, and transmissible encephalopathy in mink. Monitoring of all of these TSEs is occurring, and active research is also ongoing on these conditions. There has been a large increase in the efforts to eliminate scrapie in sheep. New, more accurate diagnostic tests in sheep are being developed, and when these tools become available, it may be possible to completely eradicate scrapie in sheep. Currently, there is no known risk to the cattle population of the US with regard to BSE, and there is no risk to people consuming beef products in this country.

Obviously, this problem has decimated the cattle industries of the UK and other countries, and we must all continue to work hard to prevent this problem in the US. This disease illustrates how important research of cattle disease is to the health of the cattle industry and to public health and confidence.

Note: I traveled to England and Scotland in the spring of 1997. I was impressed how proactive their meat boards were to inform the public about BSE. Individual meat markets, especially in Scotland, also informed their customers about the source of their beef and made it known that the beef was from young cattle, under 30 months of age.