Diseases In Deer: EHD And CWD Explained

Deer populations have been declining substantially across North America. Diseases have their part to play in the reduction of deer numbers.

Contact local Fish and Wildlife officials to see what your state is doing to help control and combat harmful diseases. 

As far as diseases go, two main culprits are affecting deer populations. Hemorrhagic Disease and Chronic Wasting Disease. Both affect animals and hunters in different ways. 

Hemorrhagic Disease (HD)


Long before there was Chronic Wasting Disease tracked in deer, the number one disease killing off deer populations was the hemorrhagic disease. Commonly referred to as HD, this disease is caused by two very closely related viruses: the first being epizootic hemorrhagic disease (EHD), and the second bluetongue virus. 

Even with two subtypes of EHD virus and five subtypes of bluetongue in North America, the disease is often indistinguishable. Since the disease shares the same features, it is common to diagnose all of the hemorrhagic diseases as HD.

HD is not spread by contact and can only be contracted by biting flies known as Culicoides. Most people know them as “biting midges,” gnats, no-see-ums, and the like.

Symptoms to look out for in deer vary depending on how severe the deer is infected with the disease. They range from fever, swelling in the neck, tongue, or eyelids. The deer die within 1-3 days of showing symptoms and will often die near water sources.

Generally speaking, deer populations have been impacted but not to devastating levels. Most outbreaks with the heaviest loss in numbers lose around 25% of the population. So, although it is a significant ding to their numbers, it is by no means impacting much of the hunting.

Blue Tongue (BTV)

One of the subtypes of HD people may have heard about more often is Blue Tongue. The symptoms are pretty much identical to HD. 

The name derived from the parched and swollen tongues on the animals appearing to be blue. The nasal areas are affected more often and cause high volumes of discharge and stertorous respiration. 

Not all infected animals will show symptoms, and some may never show any signs. It can also be carried by livestock and domestic animals, which presents a problem for range and wildlife management in many states.

Contracted the same way as HD, blue tongue requires transmission to come from a biting midge. The result is the same, where the majority of dead animals are found near water sources. 

Deer populations have not suffered as much as other animals that have come into contact with Blue Tongue. The pronghorn antelope populations in some areas have dropped drastically due to BTV.

Chronic Wasting Disease (CWD)


Without a doubt, these days, the new “hot” disease affecting deer populations is Chronic Wasting Disease (CWD). Even outside of conservation, most people have no doubt seen “CWD Check Stations” or signs warning of CWD’s spread. 

CWD is a big game killer as it is fatal 100% of the time. It is a contagious neurological disease affecting deer species as well as elk and moose. It causes degeneration of the infected animals’ brains, resulting in emaciation, strange behavior, loss of bodily functions, and eventually death. The number of mule deer being affected by CWD is more alarming. 

Like HD, there are strains of CWD that have been found in domestic animals. Once infected by the disease, the animal’s brain will eventually break itself down until the animal loses all ability to support its life. To study the spread and prevent it from infecting many of the animals, check stations have been established in many states affected. 

Using new technology to track and trace the spread, hunters have been working with conservation officials to halt this disease. Despite there being a similar disease found in domestic animals, there has been no linked trace from wild animals to domestic livestock. 

CWD is similar to a disease that humans have contracted through contaminated beef. However, there are no cases of animal-to-human transmissions in the strain found in wild animals. It is recommended not to eat the brains or transport the skull, bones, and brains across state or county lines.

If you believe the animal you have taken may have CWD, it is urged not to consume the meat. Even without the link between transmission, it is best to err on the side of caution. If you are unsure, take the time to wear gloves, clean the animal very closely, and avoid handling the brains or spinal area if at all possible. 

If you have your meat processed by a butcher, be sure to inform them of your situation. They may still be able to assist you by preparing your animal separately rather than risking it with other customers.


As hunters and anglers, we are the stewards of the wild. It is up to us to work with local and state officials when facing these disease outbreaks within the animal community. 

Wildlife is a renewable resource that we all share, so take the time to educate yourself. Contact local Fish and Wildlife resource management teams for more information on how you can help. They offer classes and often need volunteers to assist check stations. 

Each state is dealing with this problem in different ways. Double-check to make sure you comply with local regulations. It is possible your state is doing it differently than a neighboring state, and you are responsible for knowing the rules.

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