Mad Cow Disease in California

What Is Mad Cow Disease?

In April 2012, the first case of mad cow disease was reported in the U.S. in six years, occurring in a dairy cow in California. A dairy cow in Alberta, Canada, was identified as being infected in August 2011.

Mad cow disease, also known as bovine spongiform encephalopathy or BSE, is a fatal disease that causes degeneration of the brain tissue in infected cows. The condition, when transmitted to humans, can cause variant Creutzfeldt-Jakob disease, or vCJD, a very rare and fatal brain disease in humans that has similar symptoms (for example, ataxia, jerky movements, seizures) to those seen in BSE. Humans also develop dementia, memory loss, and personality changes.

The infectious particle in mad cow disease is a very poorly understood particle called a prion. A prion is not a bacterium or a virus; it appears to be a modified form of protein that can be transmitted by eating prion-contaminated tissues. Mad cow disease is thought to have begun as a result of feeding cattle meat-and-bone meal that was made from BSE-infected cattle products from either a spontaneously occurring case of mad cow disease or scrapie-infected sheep products (scrapie is a similar prion disease of sheep).

The infectious prion in cows with mad cow disease is found in the brain, spinal cord, and some parts of the central nervous system. The prion can be transmitted to humans that consume these parts of the cow; alternatively, the infection can also spread through meat that has been in contact with infected tissue or that was processed in contaminated machinery. There is no effective treatment for vCJD or BSE.

What Happened When California Found Mad Cow Disease?

Regarding the California case, public health officials pointed out that this particular case should not be alarming to humans because it occurred in a dairy cow that was not destined for human consumption, and, more importantly, that this case did not result from the cow eating a contaminated food source (meaning that other cows who ate the same food meal are not at risk). The California Department of Food and Agriculture (CDFA) confirmed these facts in a press release dated Apr. 24, 2012. In the statement, CDFA secretary Karen Ross stated, "Milk and beef remain safe to consume. The disease is not transmitted through milk. Because of the strength of the food protection system, the cow did not enter the food or feed supply. There are numerous safeguards in place to prevent BSE from entering the food chain."

Indeed, legislation has been enacted over the past decades to protect consumers from mad cow disease. According to the CDFA statement, "Feed restrictions in place in California and around the country for the last 15 years minimize that risk to the greatest degree possible." Since August 1997, the U.S. FDA has not allowed most parts from cows to be used to make food that is fed to other cows, protecting healthy cows from getting BSE by ensuring they do not receive contaminated food supplies. Further, in 2009, the FDA ruled that high-risk cow parts are not to be used in making any type of animal feed.

The U.S. Department of Agriculture (USDA) also has issued regulations ensuring that ill-appearing cows (that may be suffering from BSE) not be used for making human or animal foods. High-risk cows and cow products from other countries are banned from being imported to the U.S. Public health agencies also maintain strict surveillance programs to screen for the presence of BSE. The California case was the result of such screening; according to the CDFA, "The detection of BSE shows that the surveillance program in place in California and around the country is working."


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Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease REFERENCES:

United States. California Dept. of Food and Agriculture. "Statement from CDFA Secretary Karen Ross on USDA Announcement of Detection of BSE." Apr. 24, 2012. <>.

United States. Centers for Disease Control and Prevention. "BSE (Bovine Spongiform Encephalopathy, or Mad Cow Disease)." Mar. 17, 2011. <>.

U.S. Food and Drug Administration. "All About BSE." Feb. 23, 2011. <>.