Mad cow disease again... or it was present all the time?

[Guest guest]

A cow from a California dairy farm has been discovered to have mad cow disease,

the U.S. Department of Agriculture announced yesterday. The agency says

that consumers have nothing to worry about; after the cow died it had been slated for use in nonedible products, so there was never any danger

that infected meat would enter the food chain. Milk has not been shown to transmit the disease, and agency authorities say that this is an isolated case.

Nevertheless, some groups—including the Consumer’s Union, a nonprofit organization that publishes Consumer Reports magazine—say the case indicates that the Department of Agriculture’s surveillance program is " way too small. " Out of the 90 million cattle in the U.S., just 40,000 cows are tested for mad cow disease each year.

In response to consumer worries, two major grocery store chains in South

Korea have temporarily refused to sell U.S. beef. So is America’s beef safe? And are we doing everything we can to protect consumers from mad cow disease?

What is Mad Cow Disease?

The scientific name for mad cow disease is bovine spongiform encephalopathy,

or BSE. It’s named for the spongy remnants after the disease eats away the cow’s brain and spinal cord. Renegade proteins called prions cause the destruction and, eventually, the cow’s death. Although BSE is not contagious, it can spread to other cows if the brain and spinal tissue of an infected cow make it into the herd’s food supply.

When humans eat meat that has come into contact with the brain or spinal

material of an infected cow, the person can develop a form of Creutzfeldt-Jakob disease. CJD is a fatal neurodegenerative disorder that can arise spontaneously or by heredity, or can be acquired by exposure to brain or nervous system tissue through medical procedures. When humans acquire the disease by eating cows with mad cow disease, they develop a variant type of Creutzfeldt-Jakob disease called vCJD, which invariably causes death.

There has never been a documented case of vCJD that was caused by American beef, but a huge outbreak of mad cow disease in Great Britain in the 1980s and early ’90s is believed to have been responsible for the

deaths of 180,000 cows

and up to 150 humans by vCJD. The main reason for the outbreak was that

U.K. farmers fed their cattle the remains of other cows as a source of protein. " It sounds pretty disgusting, but it’s economical, " epidemiologist Morse tells PM. After the U.K. banned the use of recycled beef to feed cows, the incidence of BSE declined rapidly, he says.

For the same reasons, the United States prohibits the feeding of mammals

to ruminants such as cows and goats. Since that law was instituted in 1997, there have only been three known cases of mad cow disease found in

the U.S., and none appeared to have been infected because a farmer or rancher defied the law. In those cases and this week’s, the disease appeared to have arisen spontaneously through a mutation. Nasia Safdar, infectious disease physician for the University of Wisconsin Hospital, says that molecular texts on neural tissue can distinguish between BSE cases caused by bovine cannibalism and those that arose spontaneously.

How to Test for BSE

In its efforts to control BSE, the US Department of Agriculture tests about 40,000 cows annually. The inspectors test cows at random, and also

test any cow that shows signs of neurological problems. These symptoms include stumbling, inability to walk, and changes in milk production.

While there are some methods of testing live cows for BSE, none of those

methods are completely reliable. The most reliable method—and the method used by the USDA—is to slaughter the animal and send its brain samples to a lab. At the lab, the brain is inspected for lesions or spongy structure. The tissue is also analyzed to see if it contains the misfolded proteins that are responsible for the disease. If a cow is found to have BSE, it is destroyed.

Statistically, the USDA surveillance program is designed to detect BSE in one in a million cattle. But there are more than 90 million cattle in

the U.S., and symptoms of BSE can take months or years to show up.

Is More Testing Needed?

The ban on bovine cannibalism has been the single most important step in

making American beef safer, Morse says. It has essentially eliminated the risk of spreading the typical form of BSE. The atypical form of BSE seems to be able to spontaneously arise at any time or any place, but rarely. Roth, a veterinarian and microbiologist at Iowa State University’s Center for Food Security and Public Health, tentatively estimates that only one cow out of tens of millions will spontaneously develop BSE.

The question then is: Would testing more cows do any more good? Because BSE is so rare, groups like Consumer’s Union wonder if the USDA is likely to catch it if they test only 40,000 cows per year. But Roth says

that the USDA is doing everything that should be done. " If there were more testing, it wouldn’t make our food supply any safer, " he says. " We haven’t had any cases of CJD caused by BSE, so it can’t be any safer than that. "

The New York Times reports

that after the first U.S. case of mad cow disease was discovered in 2003, the USDA tested nearly 800,000 cows and identified only two additional cases. The government concluded that the effort was overkill,

and they cut the surveillance program down to its current levels.

Morse says that testing a greater number of cows could actually cause more harm than good. " It’s very hard to do that for a rare disease, " he says. " The cost of testing would be very high. It’s a tragic disease for

both people and cattle, but we’ve seen very few cases of it. It’s so rare it’s hard to figure out a practical way to do testing. "

In addition, Morse says, testing millions of cows would lead to many false positives—instances where the test indicates that a perfectly healthy cow is infected. These false positives could harm farmers’ reputations and could result in a significant loss of income, without any health benefits to the public.

And, Roth says, even if USDA surveillance does overlook a cow with BSE, other precautions are in place to prevent the harmful prions from entering human food. Cattle showing any signs of illness are supposed to

be used only in nonfood applications, and healthy cows are butchered in

ways that prevent brain or spinal cord tissue from coming into contact with humans.

Still, Consumer’s Union argues, the ban that prevents bovine cannibalism

should be extended to other types of animals as well. " The remains of cows can be fed to pigs and chickens, and pig and chicken remains can be

fed back to cows, " the group wrote in its press release. " We believe this could allow for the spread of mad cow disease. "

Roth says there’s no scientific evidence that this statement is true. But, he says, it’s hard to prove that it’s not true, simply because BSE is so rare. Some scientists think that Britain’s BSE outbreak happened because the cows’ food was contaminated with the remains of sheep with scrapie—a disease which is very similar to BSE. " Right now the ruminant feed ban seems to have been successful, " Morse says. " My personal opinion is that we should have had a broader ban. If alternative protein

sources could be found, it would be desirable to prevent any recycling of animal products in this way, because we don’t know what else is out there. "

In the case of the cow that was discovered this week, it appears workers

noticed that the cow was sick and reported it, which was exactly what they’re supposed to do. But sometimes sick cattle do slip through into the food supply, Morse says. He thinks that the USDA could do a better job at ensuring that sick cattle don’t make it into the food supply, and

that fairer incentives could help farmers to report sick cattle.

But overall, Roth and Morse feel confident that consumers of American beef are safe from mad cow disease. " When I eat a hamburger, I’m less worried about getting BSE than I am about getting an E. coli infection, which can be nasty and are far more common. "

Tags:

degenerative disease, usda, mad cow disease, CJD, bovine spongiform encephalopathy, mad cow, vCJD, BSE

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