Bovine spongiform encephalopathy (BSE)—also known as mad cow disease—is one of several neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs). It is a fatal brain disease in cattle that may develop spontaneously or originate from feeding by-products of beef and other ruminants. It has not been detected in cattle of U.S. origin. However, the U.S. Dept. of Agriculture and the Food and Drug Administration acknowledge regulatory gaps in testing cattle and managing animal by-products in the food supply.
These regulatory bodies issued several voluntary guidelines to food and supplement manufacturers to further reduce the risk of mad cow disease in the U.S. Yet, FDA suggested earlier this year that only 28% of feed manufacturers are compliant with these guidelines. Based on annual cattle slaughter statistics and current testing practices, mad cow disease may enter the nation’s food supply.
Studies in the early 1990s demonstrated that an infectious agent was insensitive to treatments that inactivate DNA and RNA but whose infection was abolished when subjected to protein denaturants. This unique infectious agent is called a prion (for proteinaceous infectious particle). Prions are normal components in most if not all mammalian cells. An infective prion usually found in brain tissue of infected animals results in an abnormal protein folding of the normal prion. The prototype of all prion disease is scrapie, which was observed in sheep and goats as far back as the early 18th century. Human prion diseases are rare (1–2 cases per million people).
TSE is a family of human and animal fatal diseases causing irreversible brain injury. The common form of TSE in humans is Creutzfeldt-Jakob disease (CJD). First described in the early 20th century, it is manifested by progressive brain damage in the elderly (loss of memory and ability to think, with eventual loss of sight and ability to speak or feed themselves). A variant form of CJD (vCJD) is associated with BSE and is thought to be caused by dietary exposure to contaminated beef products. Typical symptoms involve psychiatric features, e.g., hallucinations.
Outbreaks of vCJD in the United Kingdom, attributed to consumption of contaminated products associated with BSE cattle, have shown only a modest increase during the past several years. However, there is a lingering uncertainty about the extent of the vCJD outbreak because the incubation period ranges from 18 months to as long as 30 years. Because of the measures to eliminate both animal and human exposure to BSE from 1987 to 1997, outbreaks of vCJD should remain small.
The potential for human-to-human spread of vCJD via blood products, organ transplants, or contamination from surgical instruments may be very real. Prions are very resistant to heat, irradiation, and commonly used germicides and disinfectants. Boiling, quaternary ammonium detergents, iodine, formaldehyde, glutaraldehyde, phenol, ethylene oxide, ionizing, and x-ray irradiation are ineffective. In fact, it is recommended that nondisposable surgical instruments be immersed in 1 N sodium hydroxide for 1 hr before autoclaving at 134°C for at least 20 min. Thus, the U.S. and other countries excludes blood donations from anyone who has lived in or visited the UK for a cumulative period of 6 months during 1980–96.
BSE has not occurred in the U.S. or any other country that has historically imported little or no cattle or beef products from the UK. However, there is concern whether the bovine-adapted scrapie agent has recrossed the species barrier to sheep, carrying its newly acquired ability to infect humans. This has not yet been demonstrated, but only inferred from incidence data.
Here’s a brief history of U.S. regulatory activity regarding BSE: In 1989, the U.S. prohibited importation of cattle and edible animal products from countries reporting BSE cases. In May 1990, USDA tested suspicious cattle for BSE. In 1993, USDA initiated random sampling of downer cows at slaughter. In 1997, the U.S. expanded its importation ban to all ruminants and ruminant products from any country at risk from BSE, and USDA and FDA banned use of ruminant protein in ruminant feeds. In October 2000, USDA reported absence of BSE in 11,700 examined cattle brains. And in January 2001, FDA proposed a new detection and surveillance plan directed at TSEs.
Many public health experts suggest that the risk of contracting vCJD from food, vaccines, and dietary supplements is remote and only theoretical. Yet, to prevent the disease from taking hold in this country, the U.S. must:
• Eradicate scrapie from the U.S. sheep population.
• Support additional research to better understand the epidemiology of chronic wasting disease in game animals (e.g., elk, deer) and its potential spread to the cattle population.
• Develop sensitive and specific in-vitro and in-vivo tests to (a) detect infectious prions in human vaccines, human and veterinary medicines, and the food supply, and (b) enable public health organizations and regulatory agencies to conduct a more effective worldwide surveillance program.
• Increase surveillance and prohibition of meat or offal importation as unfit for human consumption, and develop an improved tracking system of imports of such risky bovine materials and by-products.
• Implement a compulsory notification for BSE and related TSEs.
• Impose product labels listing ingredients such as bovine pituitaries and adrenals.
• Partner with the World Health Organization and other organizations to coordinate a unified global surveillance.
The financial impact on the beef industry in England and Europe has been devastating. Solutions to these issues must be resolved with solid science and quickly implemented if indeed there is a human health risk!
A Hot Topic session on BSE will be presented on Tuesday morning, June 26, 2001, during the IFT Annual Meeting in New Orleans, La.
by STANLEY T. OMAYE