On the Alert for Mad Cow Disease
The tantalizing connections — maybe — between beef, prions, and Alzheimer's disease
Nobody survives mad cow disease. The human form of this illness, called variant Creutzfeldt-Jakob disease (or vCJD), closely mirrors dementia in its symptoms. It is caused by abnormally folding proteins, called prions, which attack the brain and nervous system. Prions are the only known non-DNA agents that can infect and replicate themselves within a host.
Four people are known to have contracted and died of vCJD in the U.S. Those people are believed to have eaten meat from outside this country.
More than 20 cases of mad cow have been detected in Canada, and the U.S. imports about 14 percent of its beef from Canada and other countries.
The disease first appeared in the 1980s in England, where more than 100 people died and scores of cattle were executed. At its peak in the ’90s, about 4.5 million cattle were destroyed because they were at risk for bovine spongiform encephalopathy (BSE). Some estimate that about three farmers a week committed suicide during this time.
BSE emerged in the cattle industry because of forced cannibalism. Ranchers gave scraps of slaughtered cattle to other cows. But when those cows ingested the neural tissue of infected cows, they, too, developed BSE. Britain responded to the crisis by immediately banning all mammalian protein from being included in cattle feed.
The U.S. responded by implementing a feed ban in 1997, which outlawed the feeding of most mammalian tissue to cattle. But some farmers continued to feed cattle tissue to their chickens — then fed fowl byproducts back to the cows. Other farmers included restaurant leftovers, which may have included meat, in food for their herds. But prions easily survived the loop from cow to chicken and back to cow — so the practice was finally banned in 2004.
At the time of the mad cow crisis, the U.S. tested only 2 percent of all its downer cows (cows that can’t stand on their own). Since mad cow had not yet shown up with the human population, the justification went for such a small amount of testing, researchers did not believe the American food system had been contaminated.
“We didn’t have a problem like [in] England,” said Dr. Amesh Adalja, an infectious disease physician at the University of Pittsburgh Medical Center.
“This didn’t come over to the United States, so we’re not going to find the same response,” he told LifeZette. The whole thing never even went through the Centers for Disease Control and Prevention — all the decisions were left to the Department of Agriculture.
New research from Yale University links Alzheimer’s and mad cow by showing that prions interact with the beta-amyloid proteins that cause the plaques in Alzheimer’s.
The consensus among researchers was that the disease was rare. James Cullor, director of the UC Davis Dairy Food Safety Laboratory, said in a media release, “When you look at the big picture, the risk seems very low. The reason I say that is we have physicians at the local level — in the farming communities, in big cities, big places like Stanford and UCLA and Johns Hopkins and physicians all over the United States, watching for this disease to show up in humans, and it’s just not there. I think that supports the premise that the risk is very low to the human population.”
But there’s no way for consumers to take precautions against eating contaminated meat, either. Meat packers don’t put BSE-free labels on their products. Unless consumers are willing to pay the extra tab for fully organic beef, there’s a continued risk they could be purchasing bad meat.
Today, we test only .1 percent of our cattle for mad cow disease. The American beef industry has a robust system of interlocking checkpoints, said Dr. Adalja, to make sure contaminated meat does not enter the human food chain. Cows are no longer fed ruminant remains, and any cows that exhibit symptoms are not slaughtered for human consumption.
However, more than 20 cases of mad cow have been detected in Canada — and the U.S. imports about 14 percent of its beef from Canada and other countries.
- Four deaths associated with it
- Caused by ingesting meats from outside U.S.
- Heat does not eliminate disease-causing prions from food
Dr. Adalja conceded this could be a risk factor: “There are concerns when people are consuming beef from other countries that may or may not have the same robust measures to prevent mad cow. It’s much more difficult when you’re using imported beef because you have less control over those regulations. But there are important guidelines from WHO [the World Health Organization] on how to feed cattle that all countries must follow.”
Still, some people question whether the U.S. system is really all that robust. Cattle ranchers are not banned from feeding all ruminant remains to their animal — just the remains of cows 30 months or older. Technically, at-risk materials — such as brain and spinal cord tissue — from younger cows can still be fed to various animals.
Prions can also have an incubation period of up to five years, which means symptoms may not always be detected in cows scheduled for slaughter. Glen Osterhout, an organic cattle rancher in Declo, Idaho, said feedlot ranchers will give just about anything to their cows.
“Most feeders — they like to turn those cattle in about 90 days, when they’re just barely big enough to butcher,” he said. “They give them growth hormones and swamp them in real rich feed.” He added, “When you buy beef out of a supermarket, they feed them just about anything they can get a hold of.”
We don’t test more of our beef because mad cow hasn’t yet shown up in people within the U.S. who have consumed American-bred beef. However, there may be more evidence of prions in the food chain than previously thought.
New research from Yale University links Alzheimer's and mad cow by showing that prions interact with the beta-amyloid proteins that cause the plaques in Alzheimer's. Dr. Claudio Soto, a researcher on that study and a faculty member at the University of Texas Health and Science Center, said in a media release, "Our findings open the possibility that some of the sporadic Alzheimer's cases may arise from an infectious process, which occurs with other neurological diseases such as mad cow."
There have been only four confirmed cases of mad cow in the United States. It's probable the interlocking surveillance of our beef industry is working to tamp down any possibility of contamination.
It boils down to two questions, said Dr. Adaljia: "How robust is your system to detect those cows and remove them from the system? Are you able to detect those cases and prevent them from getting into the human food supply?"
While the answer to the latter question may be yes — there are still some other unanswered questions about the safety of American meat.