It is thought the prions that cause BSE in cattle, if transmitted to humans, cause the invariably lethal dementia known as new variant Creutzfeldt–Jakob disease. Despite a low disease prevalence in humans and the enforcement of a zero tolerance for infected animals, there may be a reservoir of individuals who are infected but asymptomatic. These people may then infect others through donated blood or surgical instruments.

The only available diagnostic procedure requires tissue biopsies from brain or tonsils, but a simple and reliable test is urgently needed to help prevent the spread of disease. In March Nature Medicine a team from the Roslin Institute in Scotland report the first identification of a molecular marker that is easily detectable in readily accessible tissues.

Most research has attempted to identify brain-specific genes that undergo expression changes upon prion infection. But Miele et al. reasoned that prions replicate in lymphoreticular organs (spleen, tonsils and lymph nodes) long before they reach the central nervous system. Using differential display analysis of cDNAs they detected a dramatic decrease in the RNA for the erythroid differentiation-related factor (EDRF) in these organs and in the blood and bone marrow of the BSE-infected animals (Nature Med 2001, 7:361-364).

In an accompanying editorial (Nature Med 2001, 7:289-290) Adriano Aguzzi comments "EDRF may be a good diagnostic marker, whether it actually participates in disease pathogenesis or not. Future studies are required to determine the point during the course of the disease at which down-regulation of the transcript occurs in cows and — hopefully — in humans."