Research and surveillance effort for chronic wasting disease (CWD) show the disease continues to spread among deer herds in several states, generating pressure for changes in regulations and management.
CWD, a fatal prion disease related to bovine spongiform encephalopathy (BSE) and the human variant Creutzfeldt-Jakob disease (CJD), affects deer and related cervids such as elk and moose. CWD has not been shown to affect cattle or other non-cervid species, but concerns persist over the potential for mutations that could allow transfer across species.
CWD originally was identified in a captive deer herd in Colorado in the 1970s, and while it now occurs in wild herds, numerous game farms and deer farms have experienced outbreaks, prompting calls for tighter biosecurity in the captive-deer business.
In Texas, according to news reports, of 50 confirmed CWD cases, 27 were white-tailed deer in breeding pens, five were at breeder release sites, and one was a free-ranging white-tailed deer. Wild mule deer account for 16 cases, and one case was a free-ranging elk.
In Wisconsin, the disease has been found in 43 of 72 counties since the first confirmed cases in 2002. According to the Wisconsin Wildlife Federation (WWF), more than 9% of deer tested in Wisconsin in 2015 were CWD-positive, a 50% increase from 2014.
In recommendations sent to Wisconsin’s governor, the WWF has called for double fencing on all captive-deer facilities to prevent fenceline contact and possible disease transfer between captive and wild deer. The group also recommends that:
· Captive cervid farms be required to inspect their exterior fences at least monthly and immediately after any major wind storms in their locality.
· If a captive cervid farm in Wisconsin becomes infected by CWD that, unless double fenced, the property be depopulated within 30 days.
· Captive cervid farms in the state be required to maintain liability insurance to cover any costs and damages to the state of Wisconsin, including the wild deer herd resulting from any escape of cervids from the farm.
The group also calls for increased CWD sampling, funding and transparency in reporting CWD cases on deer farms and escapes from cervid farms.
In one piece of good news, researchers in Wyoming have found evidence that some elk might have varying levels of tolerance to the disease, which generally is considered 100% lethal. Over a 12-year study in a captive elk herd with a high level of exposure to CWD, the Wyoming researchers found that some animals that contracted CWD died relatively quickly. Others lived four or five years, and one cow elk is still alive after 12 years of exposure. The researchers, from the University of Wyoming and the Wyoming Fish and Game Department, suggest that natural selection for the trait could, over many years, lead to an elk herd with some level of genetic tolerance or resistance to CWD. Their report, titled
“Chronic wasting disease model of genetic selection favoring prolonged survival in Rocky Mountain elk,” is published in the journal Ecosphere.