Chronic wasting disease spreads with ease Decades of culling and containment may be needed.

Chronic wasting disease (CWD) is more infectious than was previously thought, say US researchers. The finding suggests that tough long-term measures are needed to contain the disease, perhaps involving the deaths of thousands of North American deer. In an experimental herd in Colorado, some 90 % of animals succumbed to the disease within four years, regardless of whether their parents were infected or not. Infection is thought to spread in urine, saliva or faeces, via routes such as shared scratching posts or contaminated grazing land. At present, up to a tenth of Colorado's 500,000 mule deer carry the disease. "Given enough time, all of the deer here will succumb, " says wildlife veterinarian Mike Miller from the Wildlife Research Centre in Fort Collins, Colorado, who studied transmission rates in deer. Since its first appearance in Colorado more than 35 years ago, the disease has spread across 12 states. In 2002, the disease appeared unexpectedly in Wisconsin, hundreds of miles to the east. Killing deer may be the only way to curb the disease. "It's an unfortunate argument in favour of stamping out the whole herd, " says infectious-diseases expert Mark Woolhouse from the University of Edinburgh, UK. In Wisconsin, authorities aim to cull the entire deer population. Colorado officials have restricted the movement of captive herds. Eliminating deer would harm the rural economy. In 2001, hunting generated more than $380 million across the United States, according to the US Fish and Wildlife Service. Some also fear that, like BSE, the disease could cross over to humans. "This is unlikely, " says Miller. No cases of the similar human variant Creutzfeldt-Jakob disease have been linked to eating venison. Cattle also seem resistant to CWD. Infectious protein might spread in urine and faeces