When it comes to confirming a potential BSE case, Canada’s policy is to test, retest and test again.
“The chance of human error is very low,” said Shane Renwick, director of animal health lab service with the Canadian Food Inspection Agency.
Renwick is one of a few scientists who saw the BSE sample from Canada’s first case in May 2003.
“It is quite a humbling experience to see the evidence of it in a brain because of the huge implications that are tied to it,” he said.
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Looking through a special microscope, the viewer can see a red background with a gold-black coloured set of granules. This is an indication of where antibodies are bound to the infectious prion.
“You don’t see the prions themselves because it a protein that is kind of an amorphous thing. It is not like a virus or bacteria where you see a cell wall,” he said.
Prions are natural elements but if an abnormality occurs, this can lead to a transmissible spongiform encephalopathy.
Canada uses the Prionics Check Western Test and the Bio-Rad kit called TeSeE, an ELISA test. Both are European Union approved rapid tests that use different techniques to flag suspicious samples. Suspects go on to the national laboratory in Winnipeg where the immunohistochemistry test, or IHC, is used.
“We routinely do a number of brain sections with the IHC when we do confirmatory testing,” Renwick said.
If the IHC confirmatory test is negative, but there was a strong screening test reaction, the lab routinely does the western blot test before the sample is declared definitely negative.
The actual sample comes from a little scoop of the brain stem, about the size of a cocktail sausage, at a specific point at the obex where the infectious prion is found.
“There is about an eighth of an inch there that you have to get. That’s the key area of brain.”
The tissue preparation is precise, labour intensive work.
The piece is run through a special blender that mixes the material with enzymes for the test. The samples are retained and frozen or stored in formaldehyde.
Canada had six inconclusive cases from rapid tests in 2004, leading to IHC investigations. Three samples were ruled negative because of technical issues with handling the rapid tests. The other three were ruled negative because the animals had another neurological disease.
In 2005, there have been two inconclusives and both were later confirmed as BSE positive. The samples came in at the end of the year but were confirmed in 2005.
This year to date, Canada has tested 32,363 cattle. In 2004, 23,550 were tested. From June 1, 2004 to June 21, 2005, the United States tested 388,309 samples.
