We’ve almost forgotten about them, but they’ve been out there for seven years — cattle with “mad cow disease” (bovine spongiform encephalopathy). In my article posted Mon., Sept. 27, on the Web site of the Canadian Medical Association Journal, I quote two Canadian experts that the risk to other cattle and humans is really limited now. I could almost hear my interviewees breathing a sigh of relief that the hard work to contain the disease in Canada seems to have paid off. In the UK, by contrast, there are still a lot of sick cattle and, more to the point, patients dying (although only one this year).

Canada’s first discovery of an affected cow was in 2003. Dr. Brian Evans, the chief veterinary officer and chief food safety officer in Canada, told me that the Canadian outbreak was traced to cattle imported from the UK. After slaughter, these animals ended up in the animal food supply. Animal feed goes through two large suppliers in Canada, where it may be mixed up and then scattered to many farms. This is a serious scenario for any foodborne disease affecting farm animals.

But putting any cattle products into cattle feed was banned in 1997. Cattle born since the feed ban are still getting sick, for which Evans blames old feed still sticking around silos and trucks. Even rice-grain-size feed can cause the disease, he says. He expects the odd mad cow to show up for the next few years. To CFIA, a mad cow is no longer news. 

There was a lot of press around the first few BSE cattle in Canada; there continues to be media coverage in the Western beef-producing provinces when another one shows up, because it’s an agricultural issue there. But I think most Canadians are unaware of how many Canadian-born cattle have BSE. I asked friends and family how many they had heard about. How many do you think we’ve had? I found this information difficult to glean from the Canadian Food Inspection Agency Web site, as the trends are not amalgamated in one place. Instead, I went to the US Centers for Disease Control site, which had a good overview chart.

Here are the Canadian cases, all in one place:

• Case 17 2010 Alberta beef cow 71 months
• Case 16 2009 Alberta dairy cow 80 months
• Case 15 Nov 2008 BC dairy cow 94 months
• Case 14 July 2008 Alberta beef cow 76 months
• Case 13 June 2008 BC dairy cow 61 months
• Case 12 February 2008 Alberta dairy (?) cow 73 months
• Case 11 December 2007 Alberta beef cow 165 months born 1994 before feed ban
• Case 10 April 2007 BC dairy cow 66 months
• Case 9 Jan 2007 Alberta beef bull 79 months
• Case 8 Aug 2006 Alberta beef cow 8-10 years (exact age not known)
• Case 7 July 2006 Alberta dairy cow 50 months
• Case 6 June 2006 Manitoba beef cow 16-17 years
• Case 5 April 2006 BC dairy cow 71 months
• Case 4 Jan 2006 Alberta Holstein-Hereford (mixed dairy-beef) 69 months
• Case 3 Jan 2005 Alberta beef cow under 7 years old born 1998
• Case 2 Dec 2004 Alberta Holstein cow over 8 years old born 1996
• Case 1 Jan 2003 Alberta cow 6-8 years old

The cases peaked in 2006 (5 cases) and 2008 (4 cases).

In 2009 CFIA changed some of its communication around such cases, and now no longer issues press releases unless a new case is epidemiologically significant (in a new context, a new strain, etc.). While CFIA says it consulted communities interested in BSE on this, I find it lamentable, as the public should be aware of any cases. Otherwise, even professionals in health and agriculture may forget that BSE is not gone.

Should Canadians be worried about the continued presence of BSE? Not in an immediate (should I eat beef?) sense. Go ahead and tuck into a steak, but mind the cholesterol. That’s because Canada has taken several major steps so far to prevent BSE from reaching the plate. They could have gone farther on a few points, but Evans and others point out that the low risk didn’t justify the expense of more drastic actions.

• 1997 – ban on feeding ruminant material to other ruminants (no cow products in cow feed)
• 2003 – removal of “specified risk material” (parts of the cow where BSE misfolded proteins are harboured) from slaughtered cattle intended for human consumption
• 2007 – removal of SRM from slaughtered cattle intended for pet food or fertilizer

Canada has a “targeted” surveillance program that identifies cattle for testing based on the “4 Ds” — diseased, dying, dead without known cause, or “down” (weak, stumbling or unable to rise). This is how all of the BSE cattle to date have been discovered. I read the case investigations following the detection of some of these cows. Each of the cows came from groups of cattle fed the same feed. These cattle were followed up with testing, unless they had already been slaughtered, which most of them had. Therefore, there is certainly a possibility that a few BSE-affected cattle have been slaughtered and eaten. We’re counting on two things to keep Canadians safe: we’ve removed the parts of the animal where BSE is usually found from the human food supply, and beef cattle are slaughtered at a young age when even an infected cow is not yet infective. That is, research shows that an infected animal can’t infect another until an older age. In fact, the research to date indicates animals are infected at a young age (in the first year of life), but don’t manifest symptoms for more than 50 months. All of the BSE-infected cattle discovered to date have been older, as the list shows.

European countries go farther than Canada, and test all slaughtered cattle for BSE. The feeling here is that this may be overkill. Understandable in the European context, where there was a major problem, with significant loss of human life and agricultural industry, but not needed here. This bet seems to have paid off, as the containment measures taken so far seem to be working.

There are some interesting unsolved controversies in BSE — and new directions in spongiform encephalopathies — that I’ll be exploring in upcoming posts.