Prions: Novel Pathogens of Environmental Concern?

Abstract

On March 13, 2006, the U.S. Department of Agriculture announced the third case of bovine spongiform encephalopathy BSE or “mad cow” disease in the United States, the eighth confirmed case in North America. A ninth case was announced a month later by Canadian officials. While North America is not expected to experience a BSE outbreak of the magnitude as that in the United Kingdom 180,927 cases as of March 1, 2006, www.defra.gov.uk , the causal link between BSE and variant Creutzfeldt-Jakob disease vCJD in humans has focused government and industry attention on preventing human exposure to the disease agent. The geographic range of a related disease, chronic wasting disease CWD of North American cervids members of the deer family , has expanded rapidly in the last six years. Once believed to be confined to parts of northeastern Colorado and southeastern Wyoming, CWD is now present in captive and wild deer populations in fourteen states and two Canadian provinces www.nwhc.usgs.gov/disease-information/chronicwasting-disease/north-america-CWD-map.jsp . Management responses in several states and provinces have involved significant reductions in wild cervid populations and depopulation of game farms. There is no evidence that CWD is transmissible to humans, however, recent research has demonstrated the experimental transmission of CWD to squirrel monkeys Marsh et al. 2005 and that CWD agent is present in deer muscle Angers et al. 2006 . These findings may intensify concern by scientists, wildlife managers, and the general public about potential human exposure to CWD agent. BSE, CWD, CJD, and scrapie a natural infection of sheep and goats belong to a family of infectious, neurodegenerative diseases known as transmissible spongiform encephalopathies TSEs or prion diseases. TSEs are characterized by long incubation periods, spongiform degeneration of the brain, accumulation of PrPSc a misfolded form of a normally benign cell-surface prion protein PrPC , loss of coordination and, in humans, personality changes and memory loss Prusiner 1998 . These diseases have long preclinical phases, and once clinical symptoms