One factor contributing to the spread of mad cow disease is the lack of an effective way to detect the malady's presence before infected animals begin showing symptoms. Currently, the only reliable way to confirm a diagnosis is with a brain biopsy or autopsy.

Michael Clinton and colleagues at the Roslin Institute in Scotland have found a clue that could yield a simple blood test. Clinton discovered that the level of a protein called erythroid differentiation-related factor was dramatically lower in blood from infected sheep and bone marrow from infected cattle. But it could still be awhile before a commercial blood test is generated. The researchers are trying to confirm their initial findings in a large set of animals as well as in humans. If all goes well, they expect to begin developing a diagnostic test.