When Canada announced its first case of home-grown BSE on May 20, 2003, the effects were immediate and devastating.
This disease still haunts the beef industry. Even now, when BSE is mentioned, it’s quick to hit the headlines.
According to the World Organization for Animal Health, 25 countries have found BSE in home-grown cattle. Great Britain has identified 181,044 cases. Canada has found 12.
Britain is unique. It is the only country that has had a BSE epidemic. It began in 1986 and peaked in 1992, when more than 36,000 cases were diagnosed. Since then, the number of cases has steadily dropped. The halt of the epidemic was attributed to implementation of a ruminant feed ban.
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The public fear of BSE stems from its association with variant Creutzfeldt-Jakob disease (vCJD) in people. Britain has had 114 confirmed cases and 47 probable cases of this neurological disease. To compare, the country has had 920 cases of the normal-occurring form of CJD since 1990. This suggests that the risk of vCJD is low, even in a country with a high incidence of BSE. It and vCJD are only diagnosed one way – a post mortem examination of brain tissue.
Though many think BSE hit Canada five years ago, the first true case was in 1993 in a cow imported from Britain in 1987. Veterinarians assumed the cow had received contaminated feed as a calf while still in Britain.
This first case triggered a rapid response. All other British imported cattle in Canada were identified and slaughtered – 100 cattle in total. This was followed by a feed ban in 1997 that prohibited feeding mineral bone meal from ruminants back to ruminants.
Most of the British cattle involved in the slaughter lived in Alberta. Because rendering and feed mixing are usually local businesses, veterinarians expected that the rest of the cases were going to occur in Alberta or have a trade link to Alberta. This has turned out to be true.
Scientific evidence suggests BSE is spread through mineral bone meal because the infectious agent can survive the temperature and pressure of rendering. This means that a feed ban should control it. However, seven of Canada’s BSE cases were born after the feed ban.
A possible explanation is contamination during processing. Because ruminant products could still be fed to hogs and poultry, a small portion of feed can still be present in the equipment that could end up in cattle feed. Considering it only takes one milligram of brain tissue to infect a calf, this is a probable route.
BSE may never be eradicated. Because it is known to spread through contaminated feed, the feed ban should eventually eliminate the type of disease that is passed from one animal to another. However, because BSE also occurs spontaneously, we can’t ever be sure it won’t resurface.
Some researchers think of BSE as a naturally occurring transmissible spongiform encephalopathy that is similar to classic CJD in people. It’s thought to occur when a prion protein refolds to create a new prion. This abnormal one accumulates in cells and destroys them. In Britain, the rendering and feeding of mineral bone meal to dairy cows artificially amplified the disease.
