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In June 2005, the second case of mad cow disease in the United States was confirmed in a cow from Washington state. Since 1986, mad cow cases have been identified in 20 European countries, Japan, Israel, and Canada. This is the first time the disease has posed a threat to U.S. cattle. |
When the U.S. Department of Agriculture announced it had identified a suspected case of mad cow disease in a Holstein cow from Washington state on Dec. 23, 2003, it was the first time the disease was found in U.S. cattle. Confirmation of a second U.S. case of mad cow was received in June 2005, although no parts of the animal ever entered the human and animal food supply. The discovery raises questions about what mad cow disease is, where it comes from, and how the disease affects humans.
What is Mad Cow?
Mad cow disease – officially known as bovine spongiform encephalopathy (BSE) – is a progressive, brain destroying disease that afflicts cattle. There are different theories about the agent that causes BSE. However, the most widely accepted theory is that the BSE agent is related to a modified form of a normal cell surface component called prion protein.
Mad cow disease gained worldwide attention in the early ’90s when it swept through the cattle industry in the United Kingdom. The epidemic peaked in January of 1993 at almost 1,000 new cases in cattle per week. By April 2005, more than 184,000 cases were confirmed in the United Kingdom. Scientists believe that the outbreak may have resulted from feeding infected sheep meat-and-bone meal to cattle, and further spread by feeding rendered bovine meat-and-bone meal to young calves.
Because the use of sheep and cattle tissue in livestock feed was probably a necessary factor responsible for the BSE outbreak in the United Kingdom, the U.S. Food and Drug Administration banned the use of that type of feed in the United States in June 1997. In late 2001, a Harvard Center for Risk Assessment study concluded that the FDA rule provides a major defense against this disease.
How Does Mad Cow Affect Human Health?
There is strong evidence of a link between BSE outbreaks in cattle and a disease in humans known as variant Creutzfeldt-Jakob Disease (vCJD). Scientists think the disease may be transmitted to humans through BSE-contaminated beef, especially beef products from the brain and central-nervous system. Both BSE and vCJD are brain-destroying diseases with unusually long incubation periods – sometimes many years. In the United Kingdom, where more than 1 million cattle may have been infected with BSE, a substantial species barrier seems to have protected people from widespread illness. However, as of June 2005, a total of 177 cases of vCJD had been reported worldwide: 156 from the United Kingdom.
The variant form of CJD should not be confused with the classic form of CJD, which is endemic throughout the world, including the United States. The variant form found in the United Kingdom predominately affects younger people and has many atypical clinical features. The median age of death of patients with classic CJD in the United States is 68 years, and very few cases occur in people under 30 years of age. In contrast, the median age at death of patients with vCJD in the United Kingdom is 28 years.
CDC Monitors Creutzfeldt-Jakob Disease in U.S.
The possibility that BSE can spread to humans has increased efforts to enhance national surveillance for CJD and vCJD. The Centers for Disease Control and Prevention (CDC), in collaboration with state health departments, plays an important role in monitoring CJD in the United States by several surveillance methods. CDC collects, reviews and actively investigates reports of possible CJD or vCJD cases and, in 1997, established the National Prion Disease Pathology Surveillance Center at Case Western Reserve University, which performs special diagnostic tests for prion diseases, including post-mortem tests for vCJD.
How You Can Protect Yourself
To reduce the possible risk of acquiring vCJD from food, travelers to Europe or other areas with indigenous cases of BSE may wish to consider either:
- Avoiding beef and beef products altogether or
- Selecting beef or beef products, such as solid pieces of muscle meat (rather than brains or beef products such as burgers and sausages) that might have a reduced opportunity for contamination with tissues that may harbor the BSE agent.
Milk and milk products from cows are not believed to pose any risk for transmitting the BSE agent.
The CDC Foundation supports a variety of programs that help CDC protect the public’s health and safety from threats like mad cow disease. Learn more about the Foundation’s healthy life stages initiatives, or how you can help.