For the first time on the West Coast, a deadly deer disease appeared, alarming researchers and raising questions about how the disease jumped.

On May 7, the California Department of Fish and Wildlife announced they had found two deer with chronic wasting disease — one in Yosemite Lakes in Madera County and another near Bishop in Inyo County.

Though CWD has been found throughout the Midwest, Canada, and East Coast, it is the first time the disease has been found on the West Coast. What’s strange is the Centers for Disease Control and Prevention says no states that border California have detected deer with the disease.

Whether CWD can jump to humans is still unclear. And while possible examples of CWD killing humans made the news in April, experts say evidence of a species leap is still circumstantial.

But the disease’s cousin, bovine spongiform encephalopathy — commonly known as mad cow disease — was linked to several human deaths in the 90s and nearly collapsed the beef industry.

Regardless of the threat, the detection of the disease has researchers thinking it’s much more prevalent than previously thought. Thus, researchers are asking for help from the hunting community.

This map shows U.S. counties that have detected CWD in deer. The map does not include Madera and Inyo counties, where deer with the disease were found in May. (CDC)

What is a Prion?

CWD belongs to a family of diseases connected by a misfolded prion protein.

Prion diseases can be caused by either infectious proteins, and it can also occur with seemingly no cause, called a sporadic version.

Researchers think some people or animals may just be predisposed to misfolded prions,  said Brandon Munk, senior wildlife veterinarian with CDFW.

In sheep and goats, the prion disease is called scrapie; in cows, spongiform encephalopathy — or mad cow; and in humans, Cruetzfeldt-Jakob Disease (CJD).

In Papua New Guinea, the consumption of human brain and spinal tissue among the Fore people caused the disease Kuru.

There are a lot of unknowns in the process, but essentially, the misfolded prion tells other proteins to misfold.

“You start misfolding a lot of prions into the disease-causing form and they start stacking, they move up into the brain and they create space,” said Munk.

Those spaces turn the brain spongelike. Prion diseases are slow-moving where it can be years before someone shows symptoms.

The shape of the proteins makes it so enzymes can’t destroy the proteins, Munk said. It takes hours-long bleach baths or thirty-minute bakes at hundreds or even thousands of degrees Celsius to break down the misfolded protein.

Deer affected by CWD become emaciated, clumsy, and listless. Animals drool and behave strangely. Once the symptoms appear, death follows quickly.

Case Western Reserve University describes prion diseases as “invariably fatal.”

Two Hunters Die of Human Prion Disease, Did CWD Jump Species?

As of yet, there have been no definitive cases of CWD jumping to humans, but scientists are still cautious.

When mad cow disease appeared in the 90s and early 2000s, the prion-shape was able to interact with humans after people consumed infected beef.

Cases of humans contracting CJD after eating venison have popped up, according to the CDC, but with no direct link to CWD. One questionable case arose in April.

That month, the Neurology Journal published a case study of two hunters known to consume infected deer meat who died of CJD in 2022.

Multiple health organizations, hunter’s advocacy groups all caution hunters about consuming and even handling deer meat suspected of being infected with CWD. Hunters are taught to look for signs of the disease.

The two doctors came to that conclusion that clusters of naturally-occurring CJD may be occurring in regions with CWD-confirmed deer populations, “hinting at potential cross-species prion transmission.”

What Does the CDC Say About the Case?

The CDC examined the case and said no strong link exists.

“We do not agree with the suggestion that these cases of CJD were caused by consumption of deer meat,” a spokesperson for the CDC said. “To date, there is no strong evidence for the occurrence of CWD in people. We reviewed both cases in 2022 and feel strongly that they are part of the normal number of cases of CJD we see in the U.S.”

The symptoms from the two men match normal CJD disease. The people who died of CJD after eating prion-contaminated beef showed different symptoms.

What’s more, prion diseases take years to cause symptoms. The two men died in areas that CWD had only been found recently.

Munk said some research shows the protein shape caused by CWD may prevent it from ever making the jump to humans.

“In order for the misfolded protein to tell the normal proteins to misfold, it has to have an attachment site and some lab work showed that there seems to be no way for that disease-causing CWD prion to attach to the human cellular, normal prion,” Munk said.

How Did the Disease Get to California Without Being Detected in Nearby States?

As how CWD spread to other states, Munk doubts researchers will ever know how the disease made the jump across Nevada or Oregon without being detection.

But the detection of the disease in two disparate counties on opposite sides of a mountain range leads to two conclusions.

“It either means there’s two different introductions, or it’s been here for a while. And one doesn’t preclude the other,” Munk said.

The disease very well could be much more prevalent than first thought and simply not detected. The other possibility is that hunters brought it over “by wing or by tire.”

“I think it most likely came here by tire,” Munk said.

Response Efforts Have Been Drastic in Preventing the Spread of CWD

When the Norwegian government detected CWD in their reindeer population in 2016, the country put out a call to hunters to eliminate an entire herd of 2,000 reindeer — nearly 6% of the country’s wild population, according to The Wildlife Society.

But even after those measures, CWD still appeared in other populations. Munk theorizes because of the slow nature of the disease, it had already spread throughout the country’s reindeer population.

Other regions have methods to mitigate CWD.

Oklahoma legislators in May approved a law allowing deer farms to release captive-bred deer into the wild to dilute the gene pool with deer researchers think may be more resistant to CWD, according to Outdoor Life.

Some hunting groups object to the plan, saying it hasn’t been researched enough before implementation.

Hunters Should Test Deer They Kill

Brains, organs, and the spine are areas that contain the most disease-affected prions. The California Department of Fish and Wildlife, taxidermists, or other agencies offer testing services for hunters.

The CDFW offers an online mortality reporting system.

The agency has been testing for the disease for decades and rules about bringing in deer from other states still stand, Munk said.

“This is the first time we’ve detected it. Just because it looks like CWD doesn’t mean it is CWD, so we want people to keep that in mind,” Munk said. “But we do want to test those animals to potentially rule out CWD or rule in CWD.”