Chronic wasting disease may transmit to humans, research finds

Chronic wasting disease (CWD), a highly infectious and fatal neurological disease that’s spreading through North American herds of elk, moose, mule and white-tailed deer, may be more transmissible to humans than previously thought. Researchers in the University of Calgary Faculty of Veterinary Medicine (UCVM) have published a paper in Acta Neuropathologica that shows there is a risk of zoonotic transmission of the prion disease.

“This is the first study to show that the barrier for CWD prions to infect humans is not absolute and that there is an actual risk that it can transmit to humans,” says Dr. Sabine Gilch, PhD, associate professor and Canada Research Chair in Prion Disease Research at UCVM. Prion diseases attack proteins in the brain, causing clumps to form and eventually, death.

Two well-known prion diseases are bovine spongiform encephalopathy (BSE), or Mad Cow Disease, in cattle and Creutzfeldt-Jakob disease in humans. “From Mad Cow Disease we know that prion diseases can jump the transmission barrier from animals to humans,” says Gilch. “During the BSE crisis, BSE was transmitted through contaminated meat or food products to humans and caused a new form of human prion disease, called variant Creutzfeldt-Jakob disease.”

Previous research into CWD has studied hunters who consume game in geographies with high prevalence of the disease in animals and found no evidence of human infection. “This study is an experimental model, yet it gives a lot of new information and insight to the zoonotic potential of CWD if you compare it with other published studies,” says lead author Dr. Samia Hannaoui, PhD, research associate in the Gilch lab.

Hannaoui and her colleagues Irina Zemlyankina, Chris (Sheng Chun) Chang and Maria Arifin took CWD isolates from infected deer and injected them into “humanized” mouse models. Over a period of years, the mice developed CWD. Further, the mice were found to shed infectious prions in feces.

“The implication is that CWD in humans might be contagious and transmit from person to person,” says Gilch.

Another “compelling” finding by the researchers is that CWD may show up differently in humans than in animals and other human prion diseases, and be difficult to diagnose with current methods used to screen for human prion disease. “Biochemically, the signature of this transmission is different from the classical signature of other prion diseases,” says Hannaoui.

“When we look at humans, we usually see a typical signature. And in this mouse model we did not find that signature, which means if this ever happens with humans, it will not look like the prion diseases that we know. It might be significantly different from whatever we know so far.”

While the study provides evidence supporting the potential of animal to human transmission of CWD prions, Hannaoui cautions more research is required. “This does not mean that CWD is zoonotic. We're far away from that,” she says. “This study is really important to make people aware that CWD in humans might be completely different from what's expected and from other known prion diseases. And that it could have the potential to transmit from human to human.”