8 Deer Diseases Every Hunter Should Know About

8 Deer Diseases Every Hunter Should Know About

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Spending time in the field means developing a relationship with the land and the animals on it, and that relationship comes with a responsibility to understand what you're looking at when something seems off. Deer populations across North America face a range of diseases that can affect herd health, meat safety, and even public health in some cases. Knowing how to recognize the signs of a sick animal — before and after the harvest — is part of being a conscientious, ethical hunter. Some conditions are purely cosmetic and pose no real concern, while others carry serious implications for whether that venison ever makes it to the table. A working knowledge of the most common deer diseases not only makes you a better hunter, it makes you a better steward of the wildlife you pursue.

Chronic Wasting Disease: The Threat Reshaping Deer Hunting

Chronic Wasting Disease is a prion-mediated neurodegenerative disease that attacks the nervous system of deer, elk, and moose, and it is always fatal. The prion spreads both directly between animals through saliva, blood, and bodily fluids and indirectly through contaminated soil, water, and plants. Key symptoms include extreme weight loss, lack of coordination, drooping head and ears, excessive drooling, and a telltale loss of fear of humans. The disease has reached alarming prevalence levels in some populations — a 2024 Wyoming Game and Fish Department report found CWD in as many as 66.3% of certain mule deer populations. Hunters in affected zones should have harvested deer tested before consuming meat, and should avoid eating the brain, eyes, spinal cord, lymph nodes, tonsils, and spleen of any harvested animal.

Epizootic Hemorrhagic Disease: The Midge-Borne Killer

Epizootic hemorrhagic disease is a viral hemorrhagic illness transmitted to white-tailed deer by small biting midges in the genus Culicoides, and it is considered arguably the deadliest deer disease in North America. Deer cannot transmit it directly to one another — the midge is the sole vector — but outbreaks can devastate local herds rapidly. Infected deer develop high fever, swelling of the face and tongue, difficulty breathing, ulcers in the mouth, and internal hemorrhaging, with many dying within days. A tell-tale field sign is finding dead deer near water sources, as the fever drives them to seek water in their final hours. EHD is especially problematic in the Southeast, Midwest, and Great Plains, and drought conditions worsen outbreaks by concentrating deer at limited water sources.

Bovine Tuberculosis: A Hunter's Field-Dressing Risk

Bovine tuberculosis is a chronic bacterial disease caused by Mycobacterium bovis that primarily affects cattle but can infect free-roaming whitetail deer through respiratory transmission. In the early stages, an infected deer may show no outward signs, but field dressing can reveal pus-filled abscesses and lesions on the chest cavity walls, lungs, and lymph nodes. As the disease progresses, symptoms include coughing, nasal discharge, difficulty breathing, and gradual emaciation. Because the disease can also pass through contact with an open wound, hunters who field dress deer are at higher risk of exposure than the general public, making disposable rubber gloves an essential piece of gear. There are no effective vaccines or treatments for bovine TB in wild deer, and active surveillance is concentrated in Michigan, Minnesota, and Indiana where the disease has been documented in wild herds.

Brain Abscess Syndrome: The Rut's Hidden Casualty

Brain abscess syndrome is a bacterial infection unique to bucks, typically caused by the skin bacterium Trueperella pyogenes entering a head wound sustained during sparring or antler casting. Once inside, the bacteria eat through the skull into the brain case, where a large, pus-filled abscess develops and puts fatal pressure on the brain. Visible signs in a living deer include head swelling, swollen eyes or joints, poor coordination, lethargy, and visible wounds on the head — though the disease is always fatal once the abscess forms. The infection can also spread into the bloodstream, affecting joints and feet, further mimicking other conditions. Hunters who spot a buck with an unusually asymmetrical head, broken pedicle, or neurological symptoms should report the animal to their state wildlife agency rather than pursue it.

Bluetongue: When a Deer's Tongue Turns Blue

Bluetongue is one of the two primary forms of hemorrhagic disease affecting whitetail deer, closely related to EHD but caused by a distinct virus. In its most severe peracute form, an infected deer can die within 24 hours of onset, exhibiting high fever, swelling of the head and neck, difficulty breathing, and the characteristic bluish coloration and swelling of the tongue that gives the disease its name. The disease is most commonly seen in late summer and early fall when populations of its Culicoides midge vector peak, and hunters may not encounter sick animals until the season opens weeks after an outbreak has already swept through. According to the Southeastern Cooperative Wildlife Disease Study, hemorrhagic disease is the most important infectious disease of white-tailed deer, having caused illness or death in deer across 875 counties in 31 states over a single decade. Unlike EHD, bluetongue more commonly affects livestock, though deer can contract it in rarer circumstances.

Cutaneous Fibromas: Deer Warts That Look Worse Than They Are

Cutaneous fibromas, commonly called deer warts, are hairless tumor-like growths caused by a host-specific papillomavirus that infects white-tailed deer and other cervids. The dark gray or black growths range in size from a fraction of an inch to several inches in diameter and are found most commonly on the head, neck, shoulders, and forelegs, though they can appear anywhere on the body. Most infected deer carry only a handful of fibromas, but over 200 growths have been documented on individual animals in severe cases — enough to interfere with the deer's vision, breathing, or movement. The good news for hunters is that the virus is species-specific and poses no risk to humans, domestic animals, or other wildlife, and the meat of an infected deer is entirely safe to eat after normal processing. Hunters should simply remove the skin around any growths during field dressing and treat the rest of the carcass as they normally would.

Nasal Bots: The Grubs Hiding in Your Deer's Head

Nasal bots are the larvae of flies in the genus Cephenemyia that live and develop inside the nasal passages, sinuses, and retropharyngeal pouches of white-tailed deer and elk. Adult female flies eject developing larvae directly into the nostrils of deer, and the larvae migrate inward, maturing before eventually exiting through the nose to pupate in the ground. Most infected deer show no visible external symptoms, though minor nasal discharge may be present, which means hunters are often caught off guard when they discover the white to yellowish-brown larvae — averaging one to one-and-a-half inches in length — while processing the head. Despite their alarming appearance, nasal bots pose absolutely no public health risk; people cannot be infected by these parasites, and the meat from an affected deer is completely safe to eat. Removing the deer's head promptly during field dressing is the simplest way to keep larvae from migrating further down the carcass.

Giant Liver Flukes: The Parasite Lurking in Your Deer's Organs

Giant liver flukes are flatworm parasites that enter a deer's digestive system as late-stage larvae living in the deer's food sources, then travel to the liver where they complete their life cycle and lay eggs that exit through the deer's feces. The eggs hatch on the ground and infect their intermediate host — mud snails — before transforming into the larvae that deer ingest, starting the cycle over. Infected deer typically show no outward symptoms, making the discovery a surprise at the gut pile: hunters may find large white or brown lesions, holes, or Swiss cheese-like scarring inside the liver, with oval, reddish-brown flukes up to three inches long living inside. Giant liver flukes are rarely fatal to deer on their own, but heavy infestations can weaken an animal significantly. Any liver showing signs of fluke damage should be discarded; the rest of the carcass is unaffected and safe for consumption.

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