Food Safety and “Mad Cow Disease”
Michael Payne, June 6, 2014
On June 2, 2014 the Centers for Disease Control and Prevention (CDC) confirmed a diagnosis of variant Creutzfeldt–Jakob Disease (vCJD) in a patient who recently died in Texas. A rare, progressive brain disease of people, vCJD is believed to result from consumption of beef products from cattle infected with Bovine Spongiform Encephalopathy (BSE), a condition sometimes referred to as “Mad Cow Disease.”
While media coverage of CDC’s announcement may have some consumers concerned, both USDA and FDA maintain the U.S. food supply is safe from BSE. The information below can help consumers understand why American beef is still unquestionably safe to eat.
What is BSE and what is its connection to vCJD?
Bovine Spongiform Encephalopathy (BSE) is a degenerative neurological disease of cattle caused by mis-folded proteins (“prions”) that accumulate in the cow’s central nervous system. Over a period of years these protein accumulations crowd out and kill bovine nerve cells, causing abnormal behavior and leading to the condition’s common name of “Mad Cow Disease.” There is strong laboratory and epidemiologic evidence that BSE was historically spread in European livestock by the feeding of cattle-derived proteins back to cattle, a practice which has been banned in the United States since 1997. Contaminated feed was the cause of the BSE epidemic in the United Kingdom in the 1980s and 1990s, resulting in an decade-long outbreak involving at least 180,000 cattle. Subsequently it was determined that, on rare occasions, people consuming tissues of BSE-affected cows could develop a neurological disease that was similar to both BSE and the human malady Creutzfeldt–Jakob Disease (CJD). Ultimately some 230 human cases of this “new-variant CJD” or vCJD have been identified in people living primarily in the United Kingdom and Europe.
Is the U.S. food supply safe?
Yes. To date, there have been no cases of BSE transmission to American consumers associated with beef produced in the United States. This most recent vCJD case represents only the fourth in the U.S. since the disease was first recognized in our country about 2004. All three of the previous U.S. vCJD cases involved foreign nationals, two from the United Kingdom and one from Saudi Arabia. According to CDC, there is strong evidence indicating that all three of those patients contracted disease while in their home country rather than during their stay in the U.S. The history of this most recent fourth patient, including extensive travel to Europe and the Middle East, supports the likelihood that infection occurred outside the United States.
It is essential to put this risk in perspective. In spite of previous, historical, large-scale BSE outbreaks in other countries involving tens of thousands of cows, only about 230 people worldwide have ever developed vCJD. Those cases were derived from human populations consuming primarily beef produced in Europe and so were at highest risk. This indicates it is extremely difficult for the disease to “jump” species, even in people that are consuming affected beef. In the United States outbreaks of BSE in cattle and vCJD in people have been prevented through a multi-layered series of regulatory precautions in place since the 1990s. In the U.S., you are statistically far more likely to be hit by a falling plane or crushed to death by a falling vending machine then you are of developing vCJD.
Have outbreaks of BSE occurred in U.S. cattle?
No. The current scientific evidence suggests that very rarely, a spontaneous genetic mutation in an individual cow may allow for development of BSE. Sophisticated laboratory procedures (immune-histochemistry and Western Blot protein analysis) can differentiate between this spontaneous “atypical” form of BSE and the “typical” form associated with consumption of contaminated cattle feed. This sporadic form has been detected only three times in U.S. cattle: in Texas in 2005, Alabama in 2006 and California in 2012. In all three cases, the diseased animal was identified and removed prior to entering the human food chain. As described below, even if an affected animal had gone to slaughter, tissues which are known to contain the infectious protein are not allowed to enter the human food chain.
What safeguards are present to protect the U.S. food supply?
Since 1997, the U.S. has implemented interlocking safeguards to protect human and animal health against BSE. Centered on prohibition of feeding ruminant-derived material back to ruminants, these precautions have prevented livestock outbreaks in the United States such as occurred in the United Kingdom in the 1980s and 1990s. Worldwide, similar preventative measures have ultimately reduced the number of BSE cases detected in foreign cattle from 37,311 in 1992 to just 29 in 2011. In order to ensure that U.S. safeguards are in place and effective, regulatory agencies maintain an extensive BSE surveillance program. Since the surveillance program’s inception in 1990, more than one million U.S. cattle at greatest risk for BSE have been tested, with about 40,000 high-risk cattle tested annually. This program represents an aggressive surveillance, in fact exceeding international guidelines by 10 fold. Most importantly relative to human health, tissues derived from infected cattle that might harbor the prion protein; (so-called Specified Risk Materials including brain, spinal cord, and some small intestine) are diverted away from the human food chain at slaughter. Lastly, non-ambulatory cattle (sometimes called “downer cows”), from any cause, are also prevented from entering the human food chain.
Taken as a whole, these three interlocking safeguards (the ruminant-to-ruminant fed ban, surveillance testing, removal of Specified Risk Materials from all cattle at slaughter), have been remarkably effective in preventing BSE in cattle from entering the U.S. food supply. Collectively these safety measures have been successful in protecting both U.S. consumers and livestock from outbreaks of BSE. As an aside, a substantial body of scientific research indicates that BSE is not transmitted through milk.
What is the University of California doing to help?
The California Animal Health and Food Safety Laboratory (CAHFS), a partnership between the California Department of Food and Agricultural and the UC Davis School of Veterinary Medicine, is one of six laboratories nationally that perform BSE testing for the USDA national surveillance program. View the director’s comments on BSE testing.
The University of California assists farmers in complying with the important feed regulations that prevent BSE from entering a herd.