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Introducing zombie deer disease -

Chronic wasting disease (CWD), otherwise known as zombie deer disease, is a type of prion disease that affects hoofed ruminant mammals, such as deer, elk, and moose.

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The cause -

It's an infectious disease, although it is not caused by a bacterium or virus. Instead, it's caused by a misfolded prion protein.

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The effect -

Scientists do not yet know what causes the abnormal protein, but they do know that the misfolded prion proteins kill off brain cells and cause significant bodily dysfunction.

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Symptoms -

Symptoms of CWD include weight loss, increased drinking and urination, poor balance and coordination, as well as drooping ears and difficulty swallowing.

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Fatal affliction -

The difficulty swallowing can cause drooling (hence the name zombie deer disease) and ultimately results in pneumonia and death.

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How it spreads -

CWD passes between animals through direct contact with bodily fluids and waste, as well as through indirect contact with contaminated soil, food, and waste.

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Human transmission -

Current evidence does not suggest that the disease can be passed to humans in either of these ways. Indeed, there is no evidence of human transmission to date.

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Cannot be ruled out -

However, scientists are concerned that the possibility of this disease passing from animals to humans cannot yet be ruled out.

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Reason for concern -

The main reason for concern is that there are other types of prion disease that have been passed from animals to humans in the recent past.

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Variant Creutzfeldt–Jakob disease -

The best example of a previous animal-to-human transmission is variant Creutzfeldt–Jakob disease (or vCJD).

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Mad cow disease -

Researchers have confirmed that vCJD is caused by the same infectious agent as that which leads to bovine spongiform encephalopathy (BSE), or mad cow disease.

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Infected beef -

The BSE prion is passed from cows to humans when the latter consumes infected beef. To date, there have been around 230 cases of vCJD reported worldwide.

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Not jumping to conclusions -

However, scientists, such as Michael Osterholm at the University of Minnesota, are hesitant to make like-for-like comparisons between BSE and CWD.

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Mad cow vs. zombie deer -

According to Osterholm, there are structural differences between the BSE and CWD prions, and we “cannot know whether the pathology and clinical presentation would be comparable if transmission were to occur.”

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Experimental research -

The possibility of animal-to-human transmission of CWD is an area of active research. Let's now have a look at the results of the experimental studies thus far.

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2018 study -

In 2018, the National Institutes of Health conducted a study on macaques, which share around 93% of their genome with humans.

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Macaques -

The researchers exposed the macaques to CWD-infected brain matter and then monitored them for decades, screening their tissue using various tests.

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No evidence of transmission -

The researchers found no evidence of CWD transmission from the infected deer and elk tissue to the macaques.

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Caveat -

This is only one study, however, and according to one BBC article, there is other experimental research, some unpublished, which has found evidence to the contrary.

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2022 study -

In 2022, researchers at the University of Calgary conducted another experimental study, this time on "humanized mice."

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Mice -

Humanized mice are mice that have been genetically modified for the purpose of investigating human diseases.

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Evidence of transmission -

The researchers injected the mice with CWD isolates taken from infected deer, and they observed that over 2.5 years the mice did develop CWD.

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Atypical prion signature -

The researchers noted that the mice developed an atypical prion signature, which they took to suggest that if transmission to humans were possible, it may manifest with atypical symptoms, which would make it hard to diagnose.

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Infected fecal matter -

The researchers also observed that the mice shed infectious prion proteins in their waste. This suggests that in humans, one infected person could spread the disease to another via infected fecal matter.

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In summary -

These studies do raise concerns, but they are by no means definitive. We do not have enough evidence yet to say whether a human transmission of CWD is possible.

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Looking ahead -

Looking ahead, several expert groups are nonetheless taking steps to learn more about the disease and make plans for how to react should the worst happen.

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Contingency plan -

The Center for Infectious Disease Research and Policy (CIDRAP) has assembled a group to form a contingency plan if CWD does pass over to humans.

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Continuing research -

Meanwhile, researchers at the University of Pennsylvania have been analyzing the gut microbiota of both CWD-infected and non-infected deer, in order to learn more about the disease.

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Jury is out -

As emphasized, we cannot yet say whether people should be worried about the human transmission of zombie deer disease.

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Awaiting conclusions -

This is an area of active research that will hopefully produce findings that let us know, one way or the other.

Sources: (BBC) (The Guardian) (CDC)

See also: What is this killer respiratory disease nobody has heard of?

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