RED DEER – Every bit of information gained from BSE research is another piece in the jigsaw puzzle of brain diseases.
Researchers at the Canadian Food Inspection Agency at Lethbridge joined a contingent of international scientists trying to understand the origins and pathways of transmissible spongiform encephalopathies, those degenerative neurological diseases affecting many species, including humans, around the world.
Pathologist Catherine Graham explained testing techniques and research at the Lethbridge unit, recently named the World Animal Health Organization’s (OIE) reference laboratory for BSE for the Americas.
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“The OIE has recognized with the international trade of meat and bone meal and animal feed there is probably not a single country in the world that can claim to be completely BSE free,” she said.
Countries with negligible risk include Australia, Argentina, New Zealand, Singapore and Uruguay. Controlled risk countries are Brazil, Chile, Switzerland, Taiwan, China, Canada and the United States. Iceland and Paraguay are provisionally free, she told the recent Alberta Beef Industry Council convention in Red Deer.
Countries are required to show their BSE status to determine how much surveillance testing needs to be done each year. Canada tests about 55,000 head annually while the U.S. has cut back on its testing to about 40,000 a year.
The OIE testing categories focus on animals older than 30 months that display behavioural signs like a stumbling gait or sensitivity to sound, touch and sight.
The tests include older, downed animals, emergency slaughters or those condemned at the abattoir, those that die on the farm from unknown causes as well as older animals that appear healthy.
“The clinical signs of BSE are not specific to that disease. It is a general neurological disease,” Graham said.
BSE has been a reportable disease since 1990 and Canada’s surveillance program started in 1992.
Canada has a TSE network and each province has at least one diagnostic lab capable of initial testing. The Lethbridge lab receives samples from British Columbia, Alberta and Saskatchewan, making up 40 percent of Canada’s submissions.
Individual labs do a rapid test that takes about a day. Non-negative tests or inconclusive tests are sent to Lethbridge for lengthy procedures to confirm each case.
These tests use specific antibodies that can detect the infectious prions. There are eight to 10 antibodies used in the tests. This is similar to Europe’s procedure.
“We do a number of tests in the lab to differentiate between these strains so that we can be sure we are detecting a bovine with BSE,” Graham said.
When brain samples are submitted to the Lethbridge lab, many arrive with little history.
Researchers want that history to better estimate the animal’s age and what happened during its life so they can assign point values to the samples for OIE rules. There have been cases of BSE found four years after the feed ban and researchers want more information about what happened to confirm the feed ban is working.
All but one of Canada’s 12 cases were feed related and one was ranked atypical. The U.S. has had an atypical case, a feed related case in an imported Canadian cow and an inherited mutation that caused a change in the protein prion.
“The U.S. has had basically every strain of BSE that is out there and I don’t know that we have a full picture of what the U.S. is actually seeing in its herd,” Graham said.
Atypical BSE appears different from other strains. As testing techniques improve, more cases appear, especially in Europe. Scientists do not know if this form is spontaneous or if it is the original form of BSE that was eventually spread through the feed chain.
There is research to develop a live test for the animal and human form, variant Creutzfeldt Jakob disease (vCJD). Live tests should be capable of detecting disease before the development of clinical signs.
“The distribution of that protein is so limited that development of a preclinical ante-mortem test is a tough one and it is probably going to take another decade before we are there,” she said.
The problem with BSE is that its detection is limited to the appearance of brain lesions. No tests to date can prove its presence in other tissue or body fluid, leading researchers to look for other markers that indicate the disease is present beyond the prion protein.
More sensitive detection methods in Germany found the abnormal protein in the muscles of mice that had the bovine prion protein inserted in their DNA.
Some other scientists detected it in peripheral nerves but no one has found it in milk. If the BSE prion appears in a wider range of body parts, the list of specified risk materials could increase.
A live test for humans would be especially beneficial. As of July 2007 about 200 known cases of vCJD have been diagnosed, with 166 appearing in the United Kingdom.
Three cases were transmitted via blood transfusion.
