A study published June 16, 2026, in Science Advances by researchers at the University of Calgary and international collaborators has confirmed what wildlife scientists have long feared: chronic wasting disease prions can spread from deer showing absolutely no clinical symptoms of infection, meaning a deer that appears healthy, is behaving normally, and shows no signs of disease may still be actively shedding infectious prions in its saliva, feces, urine, and blood.
The finding has direct and immediate implications for hunters, wildlife managers, and the public health community. Chronic wasting disease (CWD) — nicknamed "zombie deer disease" for the late-stage symptoms of extreme weight loss, stumbling, and listlessness that infected animals develop — has now been confirmed in 36 U.S. states and five Canadian provinces, according to the CDC. It is the only transmissible spongiform encephalopathy known to affect free-ranging wildlife, and it is invariably fatal in infected animals. There are no vaccines and no treatments.
A concurrent study published in Scientific Reports confirmed the presence of CWD prions in the blood of healthy-appearing, naturally infected free-ranging white-tailed deer, providing direct evidence of blood-based prion shedding in animals that would pass visual inspection and show no behavioral signs of disease. Together, the two studies fundamentally challenge any assumption that visual examination can distinguish infectious from non-infectious animals.
What the Studies Found — and Why Silent Transmission Matters
The Science Advances study, led by researchers at the University of Calgary's veterinary and prion biology programs, examined the zoonotic potential of CWD prions in controlled laboratory experiments, including the question of whether prions from asymptomatic animals could transmit infection to subsequent hosts. The study focused specifically on the capacity for cross-species transmission, a question of particular importance given that another prion disease in cattle, bovine spongiform encephalopathy (BSE or mad cow disease), made the jump to humans and caused variant Creutzfeldt-Jakob Disease in a tragic outbreak that resulted in over 200 human deaths in the United Kingdom.
The Scientific Reports study, conducted by researchers from Colorado State University and collaborating institutions, used real-time quaking-induced conversion (RT-QuIC) assays and other advanced prion detection methods to test blood samples from surveillance data on naturally infected, visually healthy white-tailed deer across 37 states. The confirmed presence of CWD prions in blood samples from animals that appeared completely healthy adds a key dimension: prion shedding may begin long before any clinical signs appear, during a subclinical period that, based on the known incubation timeline of CWD, can last 1.5 to 3 years after initial exposure.
The USGS National Wildlife Health Center confirms that infected animals commonly survive for several months or longer after infection begins, passing prions into the environment throughout that period, where prions bind to soil and surfaces and can persist for years, creating a reservoir of infection that is almost impossible to eliminate from an environment once established.
| CWD Surveillance and Research Data | Detail |
| U.S. states with confirmed CWD | 36 |
| Canadian provinces affected | 5 |
| Countries with CWD | U.S., Canada, Norway, Finland, Sweden, South Korea |
| Incubation period | 1.5 to 3 years after exposure |
| Time of prion shedding onset | Begins before clinical symptoms appear |
| Transmission route | Saliva, feces, urine, blood; soil and environmental persistence |
| Treatments or vaccines | None |
| Human CWD infections confirmed | None confirmed; research ongoing |
| June 16 study journal | Science Advances (University of Calgary et al.) |
The Hunting Safety Question — What the Evidence Says About Human Risk
The CDC states clearly that CWD infections in people have never been confirmed, and that it is not currently known whether people could contract CWD. However, the agency strongly recommends caution because of the precedent set by BSE, and because scientists continue to study whether CWD could potentially affect humans through meat consumption or other exposure routes, a process that could take years to decades to answer definitively, given prion disease's extraordinarily long incubation periods.
Two cases that remain of concern — discussed in the peer-reviewed literature as possible human CWD transmissions — involved hunters who died after consuming venison from CWD-affected populations, though these cases have not been conclusively confirmed as CWD transmission to humans. As the German wildlife disease monitoring site Wild bei Wild reported, the Friedrich Loeffler Institute in Germany has initiated active CWD surveillance in German deer populations, reflecting the global concern that CWD may eventually expand beyond North America and Scandinavia.
The CDC recommends that hunters who harvest deer or elk in states where CWD is known to exist have the animal tested before eating the meat. State wildlife agencies in most affected states offer testing programs; regulations vary by state and sometimes by county. Even for animals that test negative, the CDC recommends avoiding consumption of the brain, spinal cord, eyes, spleen, tonsils, and lymph nodes — the tissues with the highest prion concentration — as a precautionary measure.
Hunters should never consume meat from an animal that appears sick, disoriented, or abnormally thin. However, the new research underscores that visual assessment alone is not sufficient; an animal can appear completely normal and healthy while carrying and shedding infectious prions. Pre-harvest testing remains the most reliable tool available to individual hunters for reducing personal exposure risk.
Frequently Asked Questions
What is chronic wasting disease, and is it in my state?
Chronic wasting disease is a fatal prion disease affecting deer, elk, moose, and related animals. The CDC confirms it is present in 36 U.S. states and five Canadian provinces. States with the highest prevalence include Colorado, Wyoming, Wisconsin, and Illinois. Contact your state wildlife agency for current CWD surveillance maps.
Can a deer look healthy and still have CWD?
Yes. The June 16, 2026 Science Advances study and a concurrent Scientific Reports study confirmed that CWD prions are present in blood and bodily fluids of animals showing no clinical symptoms. The disease has an incubation period of 1.5 to 3 years during which infected animals appear normal but may already be shedding infectious prions.
Can humans get CWD from eating deer meat?
No human CWD infections have ever been confirmed. However, the CDC continues to study the potential risk and recommends caution because of the precedent of BSE (mad cow disease) crossing to humans. The agency recommends testing harvested deer in CWD-positive areas before consuming the meat.
What should hunters do to protect themselves?
Have deer and elk tested for CWD before eating the meat in areas where the disease is known to be present. Avoid consuming the brain, spinal cord, eyes, spleen, tonsils, and lymph nodes even from animals that test negative. Do not harvest or consume any animal that appears sick. Use gloves when field dressing deer and avoid contact with the brain and spinal tissue.
Is CWD affecting the deer population significantly?
Yes. The USGS confirms that CWD has the potential to significantly reduce and endanger deer populations across affected areas. Once established in an environment, prions persist in soil for years, making eradication essentially impossible. Big game hunting contributes $45.2 billion annually to the U.S. economy, making CWD a significant economic threat in addition to a wildlife conservation concern.
