What is 'zombie deer disease' that scientists fear may spread to humans?
Chronic wasting disease (CWD) was detected in the body of a buck in Yellowstone National Park in October and has now spread to 32 states
A new case of an illness dubbed 'zombie deer disease' has sparked concerns that it could spread to humans in what scientists say could be a "slow-moving disaster".
Chronic wasting disease (CWD), which leaves animals drooling, lethargic, stumbling and with a zombie-like blank stare - hence its nickname - was detected in the body of a buck in Yellowstone National Park in October and has now reportedly spread to 32 US states and four Canadian provinces. It has reportedly been found in 800 samples of deer, elk and moose throughout Wyoming.
The spread has led experts to voice concerns of its possible leap to humans, with one expert calling it a "slow-moving disaster". CWD researcher Dr Cory Anderson told The Guardian: "The mad cow disease outbreak in Britain provided an example of how, overnight, things can get crazy when a spillover event happens from, say, livestock to people. We’re talking about the potential of something similar occurring. No one is saying that it’s definitely going to happen, but it’s important for people to be prepared."
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What is zombie deer disease?
Zombie deer disease is the name given to chronic wasting disease (CWD), which is a prion disease that affects deer, elk, reindeer, sika deer and moose. Prions proteins appear on the surface of cells, and when they become abnormal can cause diseases that are transmissible, untreatable and neurodegenerative in humans and animals.
CWD can affect animals of all ages, and some infected animals may die without ever developing the disease. Animals with CWD can take over a year to develop symptoms, but CWD is fatal and there are no treatments or vaccines.
The UK government website describes the CWD as a "highly contagious and fatal disease that affects most wild and farmed deer species", including: moose, elk, mule deer, white-tailed deer, red deer, roe deer, reindeer, North American moose (known as elk in Europe), white tailed deer (indigenous to North America), fallow deer, sika, Chinese water deer and muntjac.
It adds: "Humans aren’t affected, nor are animal products or meat such as venison."
What are the symptoms of zombie deer disease?
Symptoms develop around a year after animal gets infected. Symptoms can include drastic weight loss (wasting), stumbling, wobbliness and listlessness, drooling, aggression and other neurologic symptoms.
The symptoms are what have led many to dub CWD 'zombie deer disease' as the deer it affect resemble zombies due to their listlessness and blank stare.
The government website points out changes in behaviour including: separation from other animals in the herd; depression or blank facial expression; lowering of the head; difficulty swallowing; increased thirst and urination; drooling; pneumonia; less interest in hay but continue to eat grain; teeth grinding and nervousness and excitement.
It added that infected deer may: stumble and have poor coordination; be listless and dull; walk in set and repeat patterns; have tremors; have paralysis.
Which areas are affected by zombie deer disease?
According to the US Centers for Disease Control and Prevention (CDC), the disease was first identified in captive deer in a Colorado research facility in the late 1960s, and in wild deer in 1981. By the 1990s, it had been reported in surrounding areas in northern Colorado and southern Wyoming.
Since 2000, the area known to be affected by CWD in free-ranging animals has increased to at least 31 states across all four regions of the US. Once CWD is established in an area, the risk can remain for a long time in the environment.
A deer carcass in Yellowstone National Park tested positive for the disease in mid-November. According to the CDC: "as of November 2023, CWD in free-ranging deer, elk and/or moose has been reported in at least 31 states in the continental United States, as well as three provinces in Canada".
Cases have also reportedly been reported in Norway, Finland, Sweden and South Korea. According to the government website, there have been no outbreaks in the UK but in 2016 CWD was diagnosed in wild deer in Norway, the first cases of CWD in Europe.
Why are scientists worried it may spread to humans?
According to the CDC, there have been no reported cases of CWD infection in people to date. But it says some animal studies suggest CWD poses a risk to certain types of non-human primates, like monkeys, that eat meat from CWD-infected animals or come in contact with brain or body fluids from infected deer or elk.
However, CWD researcher Dr Cory Anderson suggested that it's important to be prepared for the possibility that the disease could spread to humans. He told The Guardian: "The mad cow disease outbreak in Britain provided an example of how, overnight, things can get crazy when a spillover event happens from, say, livestock to people. We’re talking about the potential of something similar occurring. No one is saying that it’s definitely going to happen, but it’s important for people to be prepared."
The CDC has urged people to "test hunted animals before eating meat; avoid deer and elk that look sick or are acting strangely or are found dead; use latex or rubber gloves when removing the internal organs of hunted deer, while minimising contact with the brain and spinal cord tissue; do not use household knives or kitchen utensils when handling deer meat".
It points out that since 1997 the World Health Organization has recommended it is important to keep the agents of all known prion diseases from entering the human food chain.
Is zombie deer disease curable?
CWD is fatal to animals and there are no treatments or vaccines. It can affect animals of all ages and some infected animals may die without ever developing the disease.
Prions can also remain in environments for a long time, according to the CDC, adding to concerns about the spread of CWD.
What diseases from animals have caused an outbreak in humans previously?
There have been several instances in the past where diseases in animals have spread to humans.
They include:
Rabies: This zoonotic, viral disease affects the central nervous system and, once clinical symptoms appear, is virtually 100% fatal. According to the WHO, rabies spreads to people and animals via saliva, usually through bites, scratches or direct contact with mucosa (e.g. eyes, mouth or open wounds) and in up to 99% of cases, domestic dogs are responsible for rabies virus transmission to humans.
Bird flu: Also known as avian flu, bird flu is an infectious type of influenza that spreads among birds. In rare cases, it can affect humans. According to the NHS website, there are lots of different strains of the bird flu virus and most don't infect humans but there are four strains that have caused concern in recent years. Bird flu is spread by close contact with an infected bird which can include: touching infected birds; touching droppings or bedding o killing or preparing infected poultry for cooking.
Mad cow disease: In the 1980s and 90s, bovine spongiform encephalopathy (BSE) - also known as 'mad cow disease' - was found to have spread from animals to humans in the UK after people ate cattle infected with BSE. Humans can get a version of BSE called variant Creutzfeldt-Jakob disease (vCJD), and as of 2019, 232 people have died with vCJD, according to figures from the FDA in the US. Neither vCJD nor BSE is contagious so people cannot catch it from being near a sick person or cow or from drinking milk or eating dairy products.
COVID: The COVID-19 pandemic, which affected the whole world, is believed by some to have spread from animals in a wet market in Wuhan, China, to humans.
