A team including researchers from the University of Calgary has identified the gene sequences associated with BSE in cows, a finding that they say could soon lead to the development of a cost-effective screening for the disease.
Bovine spongiform encephalopathy, or mad cow disease as it is more commonly known, is a condition that effectively pokes holes in the brains of cattle. Scientists believe cattle can become infected with mad cow disease if they eat the tissue of an animal that had the disease.
Infected animals can be carriers of the disease for years and not show any symptoms. Traditionally, tests for mad cow disease could only be done post-mortem. In the past, entire herds have had to be slaughtered because of the suspicion of infection.
But the researchers say that they have come up with a method to determine if cattle are infected months before they show any symptoms. "We … envision that we could establish a testing pipeline next to the slaughterhouses for the animals that come in there to certify them as BSE-free," Christoph Sensen, the principal investigator from the University of Calgary, told CBC News.
Sensen, collaborating with other Canadian experts and scientists from German universities, analyzed animal CNAs — DNA molecules that are circulating in blood in response to an outside stressor, like an infection.
In their study, to be published in the January edition of the journal Nucleic Acids Research, the researchers tested elk for a similar condition, known as chronic wasting disease (CWD). They fed 19 elk with pieces of brain from infected animals and left five elk uninfected to act as controls. They then took a monthly blood sample every month for about two years, after which the infected animals were euthanized.
The researchers found three DNA sequence patterns that were showing up only in the infected elk. They spotted these differing sequences about half a year before the animals died and, notably, before any physical symptoms appeared.
They ran a similar analysis on cows infected with BSE. "We found the differences there to be similar to the ones with the elk," the scientists said.
Long-term analysis of cows needed
But the researchers were able to run only one analysis with cows — about four months before they died, said Sensen. Analyzing cows is much more complicated and time-consuming than studying elk. Many more breeds of cattle have to be screened and cows take much longer to die from BSE than elk do from CWD, Sensen said.
"We do have the blood samples [of cows] in the freezer and what we need to do is the work."
"We had about $200,000 to do the elk study. For the cows, with everything that we need to do…we need about 10 times as much money."
Sensen said he hopes to study the development of BSE in cows over the next three years. He believes a simple, cheap blood test can be developed soon after the completion of that study.
An outbreak of BSE devastated British dairy herds in the 1980s, forcing millions of animals to be culled. The source has never been identified, but most experts believe cattle feed contaminated with remains of sheep infected with a similar disease called scrapie may be to blame.
Humans who eat meat contaminated by mad cow disease appear to be at risk of contracting a form of the rare and deadly brain ailment Creutzfeldt-Jakob disease. Mad cow disease is linked to the deaths of about 150 people worldwide, most of them in Europe during an outbreak that peaked in 1993.
The first case of mad cow disease confirmed in Canada was in 1993 in a cow imported from Britain. In 1997, Canada outlawed feeding cows protein from other slaughtered animals.
Canada has close to 13.5 million cows and calves, with about 5.7 million, or 42 per cent, in Alberta. Canada's total beef exports amount to $2.2 billion annually.