Genetic technologies harnessed in BSE fight.

When BSE (Bovine Spongiform Encephalopathy) struck two cows last year, one in Alberta and the other in Washington state, the effect on the Canadian cattle industry was disastrous. One of the only bright spots in the battle to restore international confidence in the safety of Canadian beef was the role played by genetic technologies.

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A key issue in handling cases of BSE is traceability. If an animal is found to have BSE or "Mad Cow Disease," how can Canadian Food Inspection Agency (CFIA) officials identify its herd of origin so that measures can be taken to isolate the disease?

The Canadian Cattle Identification Agency uses ear tags to trace an animal's movement from the slaughterhouse back to its herd of origin. Although an ear tag on the animal in Washington last December facilitated a quick trace to an Alberta farm, both the American and Canadian governments relied on genetic tests to verify this information.

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Since the BSE-infected animal discovered in Alberta in May did not have an ear tag, scientists from Bova-Can Labs in Saskatoon were asked to compare a DNA sample from the animal to a number of possible sires, and to their 460,000-sample genetic bank for cattle. This test helped CFIA trace the history of the animal's movement. Subsequently, 2,700 cattle that may have come into contact with the diseased animal and its environment were destroyed and examined. None had contracted BSE, easing concerns about food safety.

BSE is a form of Transmissible Spongiform Encephalopathies (TSE), a set of fatal nerve diseases which includes Creutzfeldt-Jakob Disease (CJD) in humans, Chronic Wasting Disease (CWD) in deer and elk, and Scrapie in sheep and goats. They are referred to as "spongiform" diseases because infected brain tissue has a sponge-like appearance when viewed through a microscope. TSEs disrupt neurons in the brain in immense numbers, eventually leading to the death of the infected individual.

While the cause of TSEs is not fully understood, it is associated with the presence of an abnormal conformation of a normal cellular protein called a prion. In a slow chain reaction, the abnormal form seems to induce normal prions to switch to the abnormal conformation, resulting in deposits in the brain and spinal chord.

Concern about BSE intensified after it was linked to some human CJD variants, which appeared to involve the consumption of meat products from BSE-infected cattle. BSE, in turn, has been linked to feed supplements containing animal protein from rendered animal parts.

Currently, there is no live animal test, vaccine or treatment for BSE. However, genetics may have a role to play in finding a solution to the disease.

Some sheep exposed to abnormal prions are less susceptible to developing clinical signs of the TSE Scrapie. This resistance is genetic and the genes code for normal prion proteins that are more resistant to induced conformational changes. Genetics is being used to screen for resistance to Scrapie, and in breeding programs to increase the frequency of Scrapie resistance.

While TSE-resistant individuals have not yet been found in other livestock, including cattle, genetic resistance in sheep suggests that the potential exits for resistance genes in other species. Ultimately, it may be possible to breed cattle that are genetically resistant to BSE.

For the present, regaining consumer and export confidence will continue to rely in part, on effective systems--such as those already in place in Australia, New Zealand and Europe--to trace the source of all meat and animals. Although ear tags follow an animal's movement from the farm to the rendering plant, a routine system to trace the origin of meat samples in North America lags behind other countries.

Genetic tests, essential in confirming ear tags and the paper trail for the two BSE-infected animals, can be applied to meat samples should the need for genetically based traceability arise.

Gerry Brown is the Vice-President of Agriculture/Biotechnology at the Saskatchewan Research Council.