Mink farmers need to be concerned about BSE for two reasons. First, mink diets sometimes contain animal protein feeds that are recognized as the source of BSE organisms. And second, a similar condition, mink spongiform encephalopathy, has been diagnosed in mink.

BSE belongs to a group of mammalian diseases known as transmissible spongiform encephalopathies (TSE's). The transmissible organisms, or agents, which appear to cause all TSE's are proteins in the central nervous system known as prions. Normally prions are harmless, but they can become misshapen and cause others to do likewise in the brain, spinal cord, eyes and intestine. They also collect as waste material in the brain, ultimately leading to the death of the afflicted animal. In the case of scrapie, a TSE affecting sheep and goats, these misshapen prions also proliferate in the placenta.(1)

TSE's which apparently occur in nature include BSE, scrapie, and chronic wasting disease (CWD), found in deer and elk.(2) There are also five rare forms afflicting humans: kuru, Creutzfeldt-Jakob disease (CJD), a variant of Creutzfeldt-Jakob Disease (vCJD), Gerstmann-Straussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI).

Additionally, TSE's have been induced in captive wild ruminants, felines and monkeys, domesticated mink(3) and laboratory rodents, among other mammals.

Classical CJD is a rare disease, affecting just 0.5-1 person per million worldwide annually,(4) with victims typically in their mid-50s. Then in the 1990s, a new variant began to crop up in Europe. Between 1994 and 2000, some 90 cases of vCJD were diagnosed in the UK, three in France and one in Ireland. A distinguishing characteristic of vCJD is the average age of the victims - just 28. Public concern soared in 1996 when the British government announced that vCJD in humans might be linked to BSE.(5)

Like kuru, vCJD appears to be transmitted to humans through the eating of infected products. Kuru is only found in cannibals who have ingested parts of the human nervous system, but the prions causing vCJD are believed to be transmitted through products containing tissues from the nervous system of BSE-infected cattle. To date, these prions have not been found in cattle muscle (i.e., beef) or in dairy products.(6) Meanwhile, the meat and other products from animals with scrapie and CWD have long been eaten by humans apparently without incident.

Research also suggests that for some TSE's, susceptibility may be linked to genetics. Not all types of sheep develop scrapie, not all types of cattle develop BSE, and only humans of an unusual genotype develop CJD or vCJD.(6)

Preventive Actions in US

Spurred on by the alarming developments in the UK, countries around the world stepped up efforts to keep their cattle free of BSE.

Principal responsibility for this task in the US rests with the Department of Agriculture (USDA), which implements programs of prevention, education, surveillance and response through its Animal & Plant Health Inspection Service (APHIS) and Food Safety & Inspection Service (FSIS). In conjunction with Harvard University, the FSIS has undertaken an evaluation of the effectiveness of USDA measures, the results of which will be available in the spring of 2001.(7)

Restrictions have also been placed on trade with countries with infected herds, while the Food and Drug Administration (FDA) has banned the inclusion of various animal proteins in ruminant feedstuffs.(8)

The American Feed Industry Association (AFIA) has also taken steps aimed at further safeguarding beef herds. It has created a certification program to ensure compliance with the FDA ban, and it has issued a call for all feed plants supplying beef and dairy rations to voluntarily stop using meat and bone meal from ruminants. However, they may continue to use blood products, gelatin, inspected meat products which have been cooked and offered for human food, milk products, and products containing only pork or horse protein.

Meanwhile, several companies have begun work to develop early-detection tests for BSE which can be run on the blood of live animals. Since BSE is not caused by a bacteria or virus, any test will involve a complex procedure and there is no guarantee one can be developed. It is nonetheless encouraging that a start is being made.

With thanks to Dr. James Oldfield, FCUSA Research Committee.

Resources:

(1) Srapie info at www.ag.state.co.us/animals/livestock_disease/scrapie.html

(2) CWD info at www.uwyo.edu/AG/CES/PUBS/Chronic.htm and selected links to the National Food Safety Database, Care and Handling of Wild Game Meats at http://home.att.net/~sajackson/wildgame.html. See also CWD fact sheet provided by the USDA.

(3) Transmissible Mink Encephalopathy (TME) info at www.aphis.usda.gov/oa/pubs/fstme.html

(4) The Centers for Disease Control and Prevention (CDC) at www.cdc.gov/nip/vacsafe/concerns/bse/cjdqa.htm and UK Department of Health at www.doh.gov.uk/cjd/cmo96_1.htm and CJD statistics at www.doh.gov.uk/cjd/cjd_stat.htm and www.cdc.gov/ncidod/eid/vol7no1/pdfs/v7n1.pdf, page 10.

(5) The Full BSE UK Inquiry Report is at www.bseinquiry.gov.uk/report/index.htm, see www.maff.gov.uk/animalh/bse and "Risks From BSE Via Environmental Pathways" at www.environment-agency.gov.uk/epns/bse_risks.htm. Also see special section at www.thetimes.co.uk/section/0,,348,00.html. Also BSE/CJD/vCJD at http://beef.org/library/cjd_bse/cjd_fact.htm, www.beef.org/library/cjd_bse/index.htm.

(6) See National Cattlemen's Beef Association (US) at http://www.bseinfo.org/resource/index.htm

(7) Food Safety and Inspection Service, USDA, Risk Analysis for BSE at www.fsis.usda.gov/OA/topics/bsemeet.htm or contact Dr. Linda Detwiler at the USDA at (609) 259-5825 or linda.detwiler@aphis.usda.gov. Also see www.fsis.usda.gov/oa/topics/bse.htm and www.aphis.usda.gov/oa/bse/ and Harvard Center for Risk Analysis: Department of Health Policy and Management at www.hcra.harvard.edu

(8) See US Food and Drug Administration at www.fda.gov/cvm/index/bse/Bse_all.pdf.

See also:

Memo to HSUS: A little science is a dangerous thing. Center for Consumer Freedom commentary on false claim by HSUS that BSE can be transmitted to pigs. (May 18, 2007)

UC Davis experts on BSE. Links to faculty members ready to discuss BSE. (Mar. 25, 2004)

"An Issue of Food Safety : Government says feed restrictions are enough to protect consumers, but some leading scientists disagree." San Diego Union-Tribune. (Jan. 4, 2004.)

USDA Makes Preliminary Diagnosis of BSE. USDA press release. (Dec. 23, 2003.)

"A Better Mad Cow Test. New screen for brain-wasting disease is faster and more accurate." On research at University of California - San Francisco, Health Day News, Sept. 7, 2003.

Bovine Spongiform Encephalopathy (BSE) Backgrounder from the U.S. Department of Agriculture and Food and Drug Administration (June 5, 2003.)

USDA Marks Progress on BSE Prevention Action Steps; Triples Number of Tests for BSE USDA press release. (Jan. 15, 2003.)

Statement by US Secretary of Agriculture Ann Veneman Regarding the GAO Report on BSE (Feb. 26, 2002.)

Harvard Center for Risk Analysis; BSE Risk Assessment Study (November 2001)

Proactive Approach Makes BSE Outbreak in United States Unlikely American Veterinary Medical Association press release. (Mar. 1, 2001.)