Mad Cow Disease in Canada Cause for Concern, Not Alarm

By Will Hueston, D.V.M., Ph.D.

Never say never. That's one lesson reinforced by the recent news that a cow in Alberta, Canada, was infected with bovine spongiform encephalopathy (BSE), or Mad Cow Disease.

Here's another: An ounce of prevention is worth a pound of cure.

In the United States, the Canadian discovery serves as a wake-up call for us not to become complacent. No cause for panic because we've taken a number of measures to be prepared over the past 15 years. At the same time, we must treat this new finding seriously and remain vigilant, continuously re-evaluating our prevention plans.

Thanks to the lessons learned from Great Britain following the discovery of BSE in 1986, the United States and Canada recognized the risk posed by BSE. Intense risk assessments beginning in 1989, and repeated by Harvard University just two years ago, confirmed that the disease could occur in the United States although the likelihood was very small. Consequently, the United States and Canada embarked on an ambitious plan to keep out BSE and to prepare for the consequences if it did occur. Subsequently, the United States and Canada enacted multiple safeguards to protect against an outbreak here. Those include:

• Import exclusions of cattle enacted in 1989
• An aggressive surveillance program started in 1990 to detect BSE in cattle should it occur
• An aggressive educational campaign for farmers, veterinarians, the food processing industry, and others begun in 1990
• A ban on rendered cattle feed to prevent recycling of potentially infective materials implemented in 1997

The safeguards have served us well. For perspective, consider that 180,000 cattle have been infected with BSE in Great Britain alone since 1986 and BSE outbreaks have occurred in almost all the countries of Europe. The recent Canada case was the first ever in a North American-born animal. This case, while tragic, does not itself herald a public health crisis; however, it serves as an excellent reminder that we should be constantly vigilant and continually re-examine our control programs.

So, how did the cow in Canada become infected?

The affected cow was more than 6 years old, suggesting that the most likely exposure to contaminated feed occurred prior to the feed ban. In general, the smaller the exposure the longer the incubation, so disease in this older animal makes sense.

As part of the educational campaign, farmers, veterinarians, and others have been instructed to watch for behavioral changes in cows. When a cow eats contaminated feed, it triggers slow and progressive brain degeneration over a period of years that ultimately results in death. We have no way to measure whether an animal has been exposed; however, the behavior of affected animals usually changes over time. In most cases, it takes more than three years before you see any abnormality and it usually begins with very mild change in behavior. The cow might show more anxiety or make exaggerated responses to sound or light.

It's important to remember that normal cattle behavior is quite variable. For instance, some animals are normally skittish, while others are calm. Consequently, the key for early detection of BSE is the farmer noticing the behavioral changes.

The public health concern is the relationship of BSE to variant Creutzfeld-Jakob (vCJD) disease in humans, a fatal brain disease that typically affects younger people. There's compelling evidence that this disease has the same cause as BSE. Exposure to BSE can happen in a couple of ways, most notably, consuming brain or spinal-cord tissue from a BSE-affected cow.

VCJD cases are relatively rare, with 135 confirmed cases in humans in Great Britain. In North America, there have been two confirmed cases, but in each the person affected previously lived in England.

Again, one case of BSE in Canada is not a cause for the Chicken Little statement that the sky is falling. However, this finding is a tremendous reminder for us to revisit existing policies, strengthen our surveillance systems, and ensure that the disease cannot spread to other cattle or to humans.

Will Hueston is the director of University of Minnesota's Center for Animal Health and Food Safety and a professor in the College of Veterinary Medicine and the School of Public Health. This column is an educational service and advice presented should not take the place of an examination by a health-care professional. To ask a health-care expert at the University a question or for more health-related information, go to http://www.healthtalkandyou.com/