As a deadly 'zombie' disease continues to spread across the US, scientists warn that humans could be next.
Known as Chronic Wasting Disease (CWD) - or "zombie deer disease" - the contagious disease attacks the brains of members of the deer family, leaving emaciated animals with a zombie-like appearance before they die.
Like Mad Cow Disease, the cause is believed to be misfolded proteins known as prions. University of Minnesota assistant professor Peter Larsen told Vox the prions "turn the brain into Swiss cheese".
The animals begin to suffer dementia and hallucinations before the symptoms worsen. They start struggling with walking and loss of bodily functions before their inevitable death.
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It's been found in 26 states across the US, as well as three Canadian provinces. It spreads through deer, elk, moose and caribou populations through contaminated bodily fluid, drinking water, soil and food. The prions can survive in the environment for years, and there is no cure.
Studies have shown it can be transmitted to other animals, including monkeys and mice with human genes. And researchers have successfully infected human cells in petri dishes with prions from sick animals.
This has led to fears that it could spread to humans next through the consumption of infected meat.
Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, made the dire warning earlier in February.
"It is probable that human cases of chronic wasting disease associated with consumption of contaminated meat will be documented in the years ahead," he told Minnesota lawmakers.
"It's possible the number of human cases will be substantial and will not be isolated events."
A study by the Centers for Disease Control and Prevention has called for more research to monitor the possibility of such inter-species transmission.
"As a precaution, hunters should avoid eating deer and elk tissues known to harbor the CWD agent (eg brain, spinal cord, eyes, spleen, tonsils, lymph nodes) from areas where CWD has been identified," it warned.