A "ZOMBIE disease" that has killed thousands of deer in the US could soon infect humans in a chilling echo of Mad Cow Disease.
Chronic Wasting Disease (CWD) has swept across 22 states in the US and health experts fear it could mutate and jump the species barrier.
Mark Zabel, an immunologist at Colorado State University, told Colorado Public Radio that CWD is a newly discovered condition and may evolve rapidly, adding: "which leads us to believe that it's only a matter of time before a CWD prion (faulty protein) emerges that can do the same thing and infect a human".
Mad Cow disease emerged in the UK in the mid-1980s after cattle ate bone meal of sheep infected with scrapie, a similar brain-wasting disease.
The disease then made the jump to people through infected beef products, causing a new variant of Creutzfeldt-Jakob Disease (CJD).
Both CJD and CWD are deadly neurological disorders - transmissible spongiform encephalopathies (TSE) - that affect the brains and nervous system of many animals, including humans.
Scientists believe something similar to the CJD outbreak could happen should a hunter eat an infected deer.
Canadian researchers found that monkeys contracted CWD after eating a deer with the disease - the first time the disease has been shown to spread to a primate through meat.
Matt Dunfee, head of the Chronic Wasting Disease Alliance in Fort Collins, Denver, told the News Observer: "While most research shows there's a robust species barrier, this recent study showed that barrier might not be quite as robust as we once thought."
WHAT IS CWD?
Chronic Wasting Disease (CWD) is a type of disease that affects the brains and nervous systems of animals.
The condition was first observed in 1967 in Fort Collins, Colorado, and has since infected wild herds of deer in 24 US states and Canada.
It has also been detected in South Korea and Norway.
CWD passes from animal to animal through prions, which are faulty proteins that affect other proteins.
Prions cannot be transmitted through the air or through touching. However, they may be transmitted through contact with infected tissue, body fluids, or contaminated medical instruments.
Different prion diseases tend to only harm certain species, but can evolve to jump the species barrier.
Early in the disease, animals may show no clinical signs.
Later on, affected animals show progressive weight loss, reluctance to move, excessive salivation, droopy ears, increased drinking and urinating, lethargy, and eventually death.
Animals will test positive for the disease long before these clinical signs appear and the majority of CWD positive animals that are harvested appear completely normal and healthy.
Source: Wyoming Game and Fish Department
It can take up to two years before signs of CWD show up after a deer gets infected.
It is known as "zombie deer" disease because it causes the animal to lose weight, become solitary and lose any fear of humans.
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The deer may start slobbering more and stares vacantly as it starves to death.
It is always fatal.