Looking ahead in the fight to halt ‘mad cow’

With “mad cow” disease suddenly high on the public health agenda, farmers, researchers and government officials are facing the inevitable “what’s next” question: What measures could stem the spread of the dreaded mind-wasting disease?

The Bush administration last week took a few of the first steps urged by many food-safety experts. New regulations will prohibit the slaughter for human or bovine consumption of “downer” cattle -- those that, due to injury or disease, can no longer walk. The initiatives will put off-limits for human consumption a wide range of bovine tissue: the eyes, brains and beef marrow of cattle older than 30 months. And they will establish a tracking system to record the whereabouts and ownership history of cattle throughout the United States.

Leon Thacker, a Purdue University veterinary pathologist, said that the new tracking system for cattle could be one of the most important measures but warned that in an industry as scattered, complex and border-crossing as cattle-farming, keeping track of each animal will be a tall order.

“We’ve talked about [a tracking system] in this country for a long time, but it hasn’t been initiated because we don’t have funding and because it’s not completely accepted among those in the cattle industry,” said Thacker. “But we need it.”

But federal officials and lawmakers from cattle-producing states continue to ponder whether additional policies should be put in place now that the first U.S. case of “mad cow” has come to light. Agriculture Secretary Ann M. Veneman last week said she would appoint an international panel of experts to consider further actions to strengthen protection against the spread of the disease.

Some experts believe the Bush administration should consider going a step beyond the measures it took last week to remove potentially diseased cattle from the food chain. Currently, if a cow or bull dies on a farm, its owner frequently will call in a company to remove the carcass and “render” it for many uses, including animal feed. Rendered bovine product is also used to provide filler in many dietary supplements, over-the-counter drugs and vaccines; to make surgical replacement tissue, gelatin and beef flavoring; and in cosmetics.

A November 2001 study by Harvard University’s Center for Risk Analysis warned that allowing this practice greatly increases the likelihood that cattle in the United States could be exposed to “mad cow” disease, in spite of a ban on imported feed that could be infected. Farmers and ranchers, the Harvard report warned, may be unwilling to send sick animals to slaughter, where they would likely be inspected and tested for bovine spongiform encephalopathy. But if the old or sick animals die untested, their possibly diseased carcasses could still find their way into the American food chain.

Thacker said the government should consider establishing a program that would essentially buy the remains of such animals, removing cattle owners’ financial incentive to recoup their losses when livestock have died.

While the United States has banned the inclusion of bovine protein in cattle feed since 1997, it is one of the only countries with a “mad cow”-control program that still allows cattle to be fed proteins from horses and pigs. While horses and pigs are not thought to be susceptible to the brain-wasting proteins associated with “mad cow” disease, some scientists have grown increasingly concerned that some animals can be “silent” carriers of diseases and have urged that they be removed from cattle feed as well.

Some food-safety groups believe that American consumers deserve more information about products that are likely to contain tissue coming from the central nervous system of a cow or bull -- the place where “mad cow” disease is believed to reside. “Bone-in” cuts of meat, such as T-bone steaks, are stripped directly from the animals’ vertebrae and may contain spinal cord tissue. And edible products such as beef stock, beef extract and beef flavoring are made by boiling down the skeleton, including the vertebral column, once most of the meat has been stripped off.

But one of the most urgent needs is also one of the toughest: developing a rapid and reliable test for “mad cow” in live animals. Although an animal’s erratic behavior can be a tipoff, currently the only way to discern whether BSE is present is to test the brain of an animal once it is dead (and, as happened in late December, possibly after its meat has gone to market).

Scientists still do not understand precisely how the disease destroys brain cells, and they’ve yet to find any unique genetic cause or contributor.

If a test could be developed for BSE before animals are slaughtered, efforts to block “mad cow” could be more effective. But veterinary and medical researchers have many secrets to crack before that can happen.