Faster, more reliable tests for "mad cow" disease are on the way, scientists say, courtesy of mice genetically engineered for the task.

Dr. Stanley Prusiner, Dr. Fred Cohen, and colleagues at the University of California - San Francisco developed the mice, which develop the disease far more quickly than cattle, as test subjects to identify infected cattle and tainted products.

"We've engineered them to have a bovine gene. In that way they've now become susceptible to mad cow disease," Cohen told Reuters. Ordinary mice are highly resistant to the disease.

At least one million cattle in Britain and France have contracted the highly contagious bovine spongiform encephelopathy (BSE), commonly known as mad cow disease. At least 20 humans are believed to have developed an unusual strain of a related condition, Creutzfeldt-Jakob disease (CJD), after eating tainted meat.

When injected with cells from infected cattle, the mice develop mad cow disease within a few months, which scientists hope to cut to 40 days or less with further adjustments. Cattle can take three to five years to display symptoms, and CJD usually takes decades to surface in humans.

One of the doctors involved in the project, Dr. Steven J. Armond, told CNN that the mice may help answer scientists' questions about the disease, such as what parts of the cattle become infected, and which animal parts are dangerous to humans.

"You could then rationally decide which parts of the cow are more concerning, (and) how long you should let cows live before making them part of the food chain. We know the incidence of mad cow disease goes up with the age of the cattle."

"Then you can make reasoned public decisions," Cohen added.

Pruisner, one of the members of the UCSF team, won the 1997 Nobel Prize for medicine for his work on prions, microscopic protein particles believed to be involved in mad cow disease.

The new test is still too slow to allow testing of individual cuts of beef, however. "I'm very fond of aged beef," Cohen said, "but this would take 100 days or so, and we don't like our beef that old."