It’s amazing how often people—and even media outlets—confuse EHD and CWD, slapping a photo of a hemorrhagic disease–ravaged deer under an article about “zombie deer” CWD. EHD and CWD are completely different beasts. EHD is fast, brutal, and dramatic: deer can die in days from high fevers, internal bleeding, and crumbling hooves. Entire herds can disappear from a region in a single season. CWD, by contrast, is typically slow and stealthy. Infected deer can look perfectly healthy for years while prions—misfolded proteins that never break down—linger in the soil, vegetation, and the environment, silently spreading the disease.
The National Deer Association (NDA) breaks it down, stating that both diseases matter, but in different ways. EHD comes fast, kills a lot of deer quickly, then may disappear until the next outbreak. CWD creeps along, slowly eroding herd health over years, but it never goes away. The NDA calls CWD the biggest long-term threat to wild deer and hunting, yet EHD is the one that can wipe out herds in a heartbeat. Facts are facts, but opinions about which is “worse” definitely vary—and the media’s habit of getting facts wrong only adds to the confusion. If hunters, wildlife managers, and the public want to understand and respond to deer disease, the first step is realizing these are two very different diseases, with very different impacts. The important thing is to understand how each works, be aware of the damage each can cause, and keep your eye on both the fast killers and the slow, invisible threats. Don’t forget to do your own research, too.
Check out the chart below from the National Deer Association:
Differences Between EHD and CWD in Deer
| Hemorrhagic Disease (EHD, Bluetongue) | Chronic Wasting Disease (CWD) | |
|---|---|---|
| Basics | EHD: Viruses spread by biting gnats in late summer. Symptoms include fever and internal hemorrhaging. | CWD: A syndrome of the central nervous system in which the brain deteriorates. Cause when normal proteins call “prions” become deformed. |
| Pathway | EHD: Cannot be spread from deer to deer, only through bites from infected insects. | CWD: Spread deer-to-deer through direct contact, or contact with the saliva, urine, feces, blood and body parts of infected deer or infectious materials in soil. |
| Victims | EHD: Bucks and does of all ages are equally susceptible to being bitten by infected insects. | CWD: Higher infection rates among bucks, particularly mature bucks, most likely because they cover more ground and contact other deer more often. |
| Location | EHD: The viruses are present everywhere in North America, but outbreaks are associated with drought and extreme heat, usually in late summer. | CWD: Present in deer or elk herds in 31 states (as of 2023). Preventing CWD’s spread to new areas is critical. Transportation of live, infected deer/elk or their parts is the primary long-distance pathway. |
| Mortality Rate | EHD: Some deer survive infection. Herd immunity/survival is higher in areas with longer historical exposure. | CWD: Always fatal. The syndrome predisposes infected deer to increased death by predators, cars, other diseases, but those that live long enough will eventually die of CWD’s direct effects. |
| Speed of Death | EHD: For those deer that die, death usually occurs within a few days of viral infection. | CWD: Incubates in infected deer for one to two years before visible symptoms appear. During incubation, deer can spread CWD to other deer. |
| Durability | EHD: Viruses cannot survive outside the bodies of the insect vector or the deer/elk host. | CWD: Infectious materials remain viable indefinitely (years) in the environment and are shed in feces, urine, saliva, blood and carcasses of infected animals. |
| Human Health | EHD: Cannot infect people, either through insect bites or through handling or consuming infected deer. | CWD: No evidence that CWD is a health issue in humans, but the Centers for Disease Control and Prevention urges hunters who harvest deer in CWD zones to submit them for testing and wait for satisfactory results before eating the venison. |
| Long-Term | EHD: Outbreaks vary locally from mile to serious, but deer populations rebound. Whitetails have lived with and adapted to these viruses for decades. | CWD: Except where prevalence rates are kept low through active management, CWD threatens to slowly erode deer productivity and reduce a population’s ability to sustain hunter harvest without declining. |
