FDA moves to minimize risks tied to mad cow disease.

SILVER SPRING, MD. -- Tracking infected cows, banning the use of cattle feed made from cow parts, and testing cows are three of the actions that the Food and Drug Administration has taken in response to the discovery of a case of bovine spongiform encephalopathy, known as "mad cow disease," in a cow that entered the United States from Canada.

Despite the flurry of news surrounding the cow, the risk that humans will develop transmissible spongiform encephalopathies (TSE) or the variant Creutzfeldt-Jakob disease is considered to be low.

"Physicians should put the risk [of developing TSE] in relative terms," said Suzette A. Priola, Ph.D., chair of the FDA's Transmissible Spongiform Encephalopathies Advisory Committee and an investigator for the National Institute of Allergy and Infectious Diseases. The risk of developing TSE in the United States at this time is extraordinarily small, she said in an interview with this newspaper.

Physicians can reassure their anxious patients that they are much more likely to get food poisoning than TSE. Also, patients concerned about blood transfusions should know that anyone who spent more than 6 months in Britain between 1980 and 1996 is still deferred from donating blood, Dr. Priola said.

The FDA's Center for Biologics Evaluation and Research (CBER) and Center for Devices and Radiological Health continue to take steps to ensure the safety of medications and medical devices in response to the discovery of bovine spongiform encephalopathy (BSE) in the United States.

Risk management strategies include the prohibition of the medical use of raw materials from countries (now including the United States) with known cases of BSE or those thought to be at risk, and the use of non-animal-derived ingredients and reagents wherever possible.

Milk-derived or hair-derived products from BSE-positive countries is permitted, along with gelatin and tallow derivatives if they are used orally or topically, noted Gerald M. Feldman, Ph.D., of CBER.

To minimize the risk of BSE-related prions being present in blood products, CBER is encouraging manufacturers to use nonbovine materials when possible and to acquire bovine materials from countries where BSE has not appeared, said Dr. Dorothy Scott of the Office of Blood Research and Review.

But the number of BSE-free countries is dwindling, so finding guaranteed pure bovine material is becoming increasingly difficult, Dr. Scott noted. But the risk of contamination can be minimized by cleaning equipment between batches of blood products, testing for TSE during the manufacturing process, and monitoring geographic sources, tissue sources, and tissue collection techniques.

Dr. Melissa A. Greenwald of CBER's Office of Cellular, Tissue, and Gene Therapies, said that CBER's proposed regulations include screening and testing potential donors of human cellular and tissue-based products for risk factors and clinical evidence of communicable disease, including TSE. Other proposed recommendations address issues of "good tissue practice," including requirements for labeling, storage, and processing. For example, specimens from each dura mater donor should be archived, and the dura mater should be processed using a validated method for minimizing TSE risk.

As for vaccines, William M. Egan, Ph.D., of CBER's Office of Vaccines Research and Review, said that master viral and bacterial seed banks derived from bovine material should be rederived to minimize risk of BSE, and only material from cows younger than 30 months should be used for vaccines and other bovine-derived material.

In addition, a package insert on products containing human serum albumin warns physicians and patients of the potential risk of transmissible disease, according to Dr. Egan.

Keeping tabs on BSE remains a challenge, since seemingly healthy cows could carry the illness, and since some cows are fed poultry feed, which may contain material banned from "official" cow feed. The FDA plans to continue to test animals and to inspect feed mills and carcass processing plants.

For the most current information on the government's efforts to minimize the spread of BSE, visit www.usda.gov/BSE.

BY HEIDI SPLETE

Senior Writer