[Animals] Does 'zombie deer disease' pose risks for humans?

[Wolf.17]

Recent cases of humans contracting sporadic Creutzfeldt-Jakob disease (CJD) have raised questions about whether a disease carried by deer may be jumping the species barrier.

"Zombie deer disease" is spreading among wildlife. But scientists haven't reached an agreement on whether the condition – also known as chronic wasting disease – can spread to humans and lead to a form of Creutzfeldt-Jakob disease (CJD).

Chronic wasting disease, or CWD, is a type of prion disease, according to the Centers for Disease Control and Prevention in the United States. It's a neurodegenerative condition that infects wildlife, including deer. It has most recently been confirmed in deer, as well as moose in Canada, after previous cases were reported in Yellowstone National Park in the United States.

No cases have yet been reported in humans, but a recent medical case report by doctors in Texas, US, on the deaths of two hunters who regularly ate meat from a po[CENSORED]tion of deer infected with CWD has raised fresh questions about a link with human prion disease. Both men died of CJD, but doctors investigating the deaths were unable to prove a definitive link to CWD. They urge for the need for increased surveillance and research to establish whether the disease can cross over into humans.

As transmissions in animals increase across North America, Scandinavia and South Korea, some experts fear the risk of transmission to humans may also be increasing. They base their concerns on experimental studies, the history of other prion diseases transmitting from animals to humans (which is extremely rare) and the potential impacts of climate change.

"As of yet, there has been no transmission from deer or elk to humans," says Jennifer Mullinax, associate professor of wildlife ecology and management at the University of Maryland. "However, given the nature of prions, CDC and other agencies have supported all efforts to keep any prion disease out of the food chain."

This is what we currently know about CWD.

What is zombie deer disease and what are the symptoms?

Chronic wasting disease is transmitted in cervids, which are hoofed ruminant mammals, such as deer, reindeer, elk and moose. Although it is an infectious disease, CWD is not caused by a bacterium or a virus, according to the US Department of Agriculture's Animal and Plant Health Inspection Service.

Instead, a misfolded prion protein causes the issue, but researchers don't yet know what causes the protein to become abnormal. Normal prion proteins potentially play a role in cell signaling. But when misfolded, they cause more proteins to misfold.

Misfolded prion proteins in the brain kill brain cells and cause bodily dysfunction, leading to unusual symptoms. Symptoms include weight loss, excessive drinking and urination, poor balance and coordination, drooping ears and difficulty swallowing. The difficulty swallowing can lead to drooling and eventually pneumonia and death. The classic symptoms – and the image of an uncoordinated, stumbling and drooling animal – have led to the term "zombie deer disease". The symptoms can take months or years to manifest, making a visual diagnosis difficult.

When prion proteins are misfolded, they become infectious, which leads to spread among wildlife. CWD spreads from animal to animal through direct contact with bodily fluids and waste and through indirect contact with contaminated soil, water and food.

Can zombie deer disease spread to humans?

The CDC estimates that in areas where the prion disease is endemic, infection rates range from 10% to 25%. In 2023, surveillance results from the Canadian province of Alberta suggest a 23% positivity rate for mule deer.

Current evidence does not show that CWD can be spread to humans when they eat the meat of an infected animal, encounter infected wildlife, or drink or touch contaminated soil or water. But researchers continue to investigate whether animal-to-human transmission is possible. "The current body of research is a mixed bag, meaning we don't know yet," Mullinax says.

Older research from the CDC, published in 2011 used the Foodborne Diseases Active Surveillance Network 2006-2007 po[CENSORED]tion survey to assess exposure risk. The survey included results from more than 17,000 participants. More than 65% of the total respondents reported eating wild game at least some of the time. The researchers were looking only at the prevalence of potential exposure, but they reported that no evidence of human transmission had been found to date.

However, prion diseases, also called transmissible spongiform encephalopathies, are present in humans. These include Creutzfeldt-Jakob Disease, which is an inherited condition, and variant Creutzfeldt-Jakob disease. The latter, researchers have now confirmed, is caused by the same infectious agent that leads to bovine spongiform encephalopathy, or BSE, also called "mad cow" disease.

https://www.bbc.com/future/article/20240219-zombie-deer-disease-risks-for-humans