Warnings that ‘slow-moving disaster’ in North America raises chances of fatal mad cow-type disease jumping species barrier

When the mule deer buck died in October, it perished in a place most humans would consider the middle of nowhere, miles from the nearest road. But its last breaths were not taken in an isolated corner of American geography. It succumbed to a long-dreaded disease in the backcountry of Yellowstone national park, north-west Wyoming – the first confirmed case of chronic wasting disease in the country’s most famous nature reserve.

For years, chronic wasting disease (CWD), caused by prions – abnormal, transmissible pathogenic agents – has been spreading stealthily across North America, with concerns voiced primarily by hunters after spotting deer behaving strangely.

The prions cause changes in the hosts’ brains and nervous systems, leaving animals drooling, lethargic, emaciated, stumbling and with a telltale “blank stare” that led some to call it “zombie deer disease”. It spreads through the cervid family: deer, elk, moose, caribou and reindeer. It is fatal, with no known treatments or vaccines.