It’s a perilous time right now for deer in America. On Monday, Minnesota officials enacted an emergency order to stop the local travel and importation of farmed deer, in hopes of slowing down the spread of a universally fatal prion disease among wild deer. Meanwhile, in Vermont, wildlife officials today announced the first known case of another deadly deer disease within the state, one that causes massive internal bleeding. Fortunately, neither illness is currently thought to be a danger to humans.
Prion diseases are caused by unassuming proteins that somehow become misfolded into a dangerous version of themselves. When a misfolded prion comes across its normal version, the latter turns rogue, too, eventually leading to a build-up of bad prions that destroy the body, particularly the brain. Some prion diseases are transmissible through exposure to infected tissue (including the cannibalism of brains); others may run in families; and some just happen spontaneously for no clear reason. All known prion diseases, in both animals and humans, are 100% fatal, though it can take years, even decades, for signs to appear following exposure.
Chronic wasting disease, or CWD, is a prion disorder that can affect a wide variety of deer, moose, and elk. Its most prominent symptom is drastic weight loss, but others include confusion, drooling, a lack of coordination, and the loss of fear around humans. Deer are usually thought to catch CWD through contact with contaminated body fluids, though it can also be transmitted through contaminated food and drinking water.
CWD is overall rare among wild and farmed deer, but many wildlife experts fear that the disease is an urgent threat that’s becoming worse. The disease can spread quickly among crowded populations once established, and its presence can linger for a long time in the soil and water where infected deer urinate and defecate (if prions weren’t scary enough, they’re also much harder to “kill” than other infectious germs). Currently, cases have been reported in 26 states, as well as in Canada and parts of Europe and Asia.
It’s this danger that compelled officials with the Minnesota Department of Natural Resources to issue their emergency order, which will temporarily stop the importation and transportation of farmed whitetail deer in and out of the state. The decision was prompted by the recent report of a CWD outbreak at a Wisconsin deer farm that sold deer this summer to seven states, including Minnesota.
“This disease poses a clear, immediate and serious threat to Minnesota’s wild deer, and these actions reflect what’s at stake,” said Minnesota Department of Natural Resources Commissioner Sarah Stromme in a statement by the agency.
This same day, the Department of Fish and Wildlife in Vermont issued their own deer-related alert, after finding the first case of epizootic hemorrhagic disease (EHD) among wild deer in at least two regions of the state.
EHD is caused by a virus (epizootic hemorrhagic disease virus) that’s transmitted through the bite of midge flies. It isn’t contagious between deer, and it’s not deadly as CWD, but EHD can cause serious, sometimes fatal, bleeding and disability. The disease has been around for a long time in the U.S., mostly in the South, but it’s expanded its range this year. In New York, it’s suspected that around 700 wild deer have died from EHD this year, a far larger toll than past sporadic outbreaks. Vermont officials believe that their isolated cases are likely related to the New York outbreaks, since some cases have bordered Vermont. Because the virus is spread by midges, though, the winter season should end the risk of transmission soon enough, at least until next spring.
EHD has never been shown to affect humans, and eating meat from infected animals isn’t considered a direct risk—that said, EHD deer may be sick in other ways, so it’s still not recommended. The risk of CWD to humans is less clear, however, since some lab studies have shown evidence that CWD can be transmitted in the lab to primates. But so far, no cases of human prion illness have ever been linked to eating or otherwise coming into contact with CWD deer. (Squirrels, on the other hand...)