Researchers develop blood test to screen mad cow disease
Researchers in Canada have developed a blood test that can diagnose fatal chronic wasting disease in elk.
Researchers in Canada have developed a blood test that can diagnose fatal chronic wasting disease in elk, and believe it may provide a cheap way to screen cattle for mad cow disease.
The test looks for signs of damaged cells in the blood, they reported in the journal Nucleic Acids Research. It may also offer a way to diagnose people with a related disease called Creutzfeldt-Jakob disease, or CJD, they said on Thursday.
"We can now take a blood sample from a live animal and look at the DNA patterns in the blood and predict six months ahead of time whether an animal is infected with chronic wasting disease," Christoph Sensen of the University of Calgary said in a telephone interview.
The secret is not finding the prions that cause mad cow disease and other so-called transmissible spongiform encephalopathies or TSEs, Sensen said. Instead they looked for circulating nucleic acids -- little bits of DNA that get spat out when distressed cells die.
The found three distinct patterns in these circulating pieces of DNA that appeared three months before the elk showed symptoms. Each pattern correlated with genetic mutations known to put the animals at higher risk of contracting the disease.
TSEs such as chronic wasting disease, mad cow disease, scrapie and CJD destroy the brain and can happen spontaneously, but are also passed from animal to animal by eating infected tissue.
Mad cow disease or BSE swept through British dairy herds in the 1980s, and infected a few people who ate contaminated beef. Overall, fewer than 200 people globally have died from CJD caught in this way.
Chronic wasting disease is also found in herds of wild elk and deer in the U.S. and Canadian west.
But every case in a cow shuts down a country's exports for a time, so cattle breeders and governments are keen for a test. Usually cases cannot be diagnosed for certain until the brain or certain other organs are examined.
Sensen's team, including an expert from the Canadian Food Inspection Agency, looked at vesicles -- little pieces of DNA that end up in the blood when a cell dies. "We are looking at the host response to the infection," he said.
"Any disease puts stress on the body. We are looking at what does the host do to rectify the attack."
Chronic wasting disease is always fatal, like BSE and CJD, but the cells of the animal struggle and Sensen said this changes the DNA in a way that can be seen in the test.
The test itself is a simple polymerase chain reaction or PCR test that amplifies the DNA so it can be sequenced.
Sensen suggests pooling the blood of several animals -- perhaps in batches of 20 or so -- and testing it all at once. If evidence of BSE is found, then each of the 20 animals in that batch could be individually tested.
His team tested 19 elk and two BSE-infected cattle from Germany and could identify the infected animals every time.
He said it will take four years to be able to replicate the findings in cattle.
"There is currently no reliable way to tell if an animal may have a prion infection before it becomes obviously sick," Kevin Keough from the Alberta Prion Research Institute said in a statement. "If there were a reliable way to know, it would be of great benefit to producers, processors and wildlife managers."
Reuters Last Mod: 31 Ocak 2009, 11:28