Genetic mutation behind some mad cow cases, study shows
Mad cow disease may be caused in some cases by a rare genetic mutation that also occurs in humans who have a related brain-wasting disease, U.S. scientists have found.
The mutation was found in a cow from Alabama that tested positive in 2006 for bovine spongiform encephalopathy or BSE, also called mad cow disease. The animal passed along the mutation to its heifer.
In Friday's issue of the journal PloS Pathogens, researchers said the 10-year-old cow had an atypical form of BSE with the same type of prion protein gene mutation as human patients with the genetic form of Creutzfeldt-Jakob disease.
Prions are infectious agents that cause diseases like CJD. Humans can also contract CJD from eating products contaminated with BSE, a form known as variant CJD.
"Our findings that there is a genetic component to BSE are significant because they tell you we can have this disease everywhere in the world, even in so-called BSE-free countries," said study author Juergen Richt, a professor of diagnostic medicine and pathobiology at Kansas State University's veterinary college.
Breeding out disease
The mutation is rare and affects fewer than one in 2,000 cattle, based on a recent epidemiological study.
The advantage of knowing BSE has a genetic component is that it opens the possibility of stamping out the disease through selective breeding and culling of genetically affected animals, said the researchers, who are working on developing such a test.
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.
The findings may lend support for the hypothesis that BSE in cattle may be traced to feed contaminated with remains from cattle or humans scavenged from the Ganges River in India, Richt and co-author Mark Hall of the U.S. Department of Agriculture said.
Two other possibilities have also been proposed. BSE in Britain may have resulted from a genetic case, or the sporadic, genetic and infectious forms of the disease found in humans may also be present in cattle, the pair wrote.
Most countries now ban the use of meat and other body parts from mammals in cattle feed. The brain, spinal cord and other tissues can carry the infectious prions.
In May, $8 million in funding was awarded to Canadian researchers working to prevent prion-related diseases, by developing a BSE vaccine for cattle and developing new food testing standards.