New vaccine research targeting chronic wasting disease (CWD) has researchers in the University of Calgary Faculty of Veterinary Medicine (UCVM) hopeful. Their study, published recently in the Journal of Biological Chemistry, found that the vaccine, tested in a mouse model, prolonged the time before infected animals developed symptoms by up to 60%.
Similar to bovine spongiform encephalopathy (BSE) in cattle and scrapie in sheep, CWD is a prion disease of members of the cervid family, such as deer, elk and moose.
Infected animals lose weight drastically (wasting) and suffer other symptoms like stumbling, lack of coordination and drooling. CWD is fatal in all cases. There is no cure, treatment or way to prevent it.
“The vaccine doesn’t prevent the disease, but it delays its onset,” said Dr. Dalia Abdelaziz, a researcher in Hermann Schaetzl’s lab at the University of Calgary in Alberta. “That’s what we want. In mice, if we are extending it for around 70 days, that’s significant, because their life span is much shorter than deer or elk. That’s why we are excited about the results. We couldn’t induce full protection, but the survival time was greatly increased.”
CWD is caused by a prion — an abnormal form of a harmless protein found in the brain. Once prions are present in the brain, they multiply by causing normal proteins to refold into an abnormal shape, the announcement said.
“The immune system of the animal doesn’t detect prions as an enemy, so there’s no immune response against the disease,” said Simrika Thapa, an Eyes High and Killam doctoral student and co-author of the study. “We are trying to create an immunogen that induces an immune response in the animal. It’s like a flu shot producing a response so your body recognizes and defends itself against the disease.”
CWD "spreading like crazy"
“There’s no treatment, and the other huge problem with this disease is it’s very contagious, so its spreading like crazy in North America,” Abdelaziz said. “Animals spread the infection, shedding it in their urine, saliva and feces, and the result is the infection is almost everywhere in the environment.”
Thapa added that CWD doesn't just affect the animals' brains, but “it’s in their muscles as well. It’s not only in the central nervous system; it’s throughout the body. When an animal dies and decomposes in the environment, they are contaminating all the plants and the soil. So, when deer eat plants or get in contact with soil, the infectious protein gets inside the body, and the infectious protein can stay in the soil for many years.”
The researchers noted that there are questions about whether CWD can jump the species barrier to infect people. That’s what happened in another prion disease called variant Creutzfeldt-Jakob disease, the human form of BSE.
“The potential of cross-species transmission into humans is an alarming issue and is still an open question,” Abdelaziz said. “There haven’t been any reported cases of CWD in people, but studies of squirrel monkeys have shown its transmissibility into non-human primates.”
Schaetzl's lab is part of a multinational consortium studying whether CWD can also infect macaques using transgenic mouse models as an additional readout.
The question now is whether the vaccine is as effective in deer. As a first step, Dr. Rob McCorkell, with the help of three veterinary students, did immunization studies in reindeer at UCVM’s Spy Hill campus.
“Our next step is to work on an oral vaccine that can be used in wildlife. You can’t vaccinate free-ranging deer by injection, so we are considering plant-based vaccines that can be eaten directly by deer and elk,” Abdelaziz said. “We are working on arranging collaborations with other facilities where it is possible to immunize and then infect with CWD to test in the real host.”
Abdelaziz added, “We have lots of future directions in this project, and we are so excited.”