Hunters should be familiar with these common sources of deer mortality. Photo Credit: John Hafner

Understanding Major Deer Diseases

  Joe Shead   FeaturedWildlife   December 15, 2022

Hunters and other predators aren’t the only causes of deer mortality. A host of diseases and parasites may infect deer, and hunters should be familiar with them. Some of these deer ailments affect single deer and are not contagious. However, some diseases can spread quickly to other individuals. Use common sense. If you observe a deer acting disoriented, looking emaciated, salivating or displaying other unusual behavior, notify your local fish and game department. If you have a valid tag during the open season, you might consider killing the animal to allow the proper authorities to examine it. Hunters are the best hope for discovering deer diseases quickly. Do your part. If you see something unusual, say something. Here’s the rundown on some of these diseases:

Chronic Wasting Disease

 

CWD is a disease that is always fatal to deer. Photo Credit: USGS / Terry Kreeger Wyoming Game and Fish and Chronic Wasting Disease Alliance

 

Chronic wasting disease makes a lot of headlines in the deer world because it is widespread (found in at least 23 states) and is always fatal to deer. CWD is caused by a misfolded protein called a prion. When prions contact normal proteins, they cause these proteins to be damaged, too. These prions accumulate in and damage an animal’s nerves, lymph nodes and brain.

During the 18- to 24-month incubation period, infected animals may look normal, although they may experience weight loss. However, once CWD takes hold, animals often lose their fear of humans, wander about aimlessly and avoid social interactions with other deer. As the name implies, infected animals literally waste away, losing excessive body mass and appearing gaunt. They may also salivate, drink excessive amounts of water and urinate frequently as a result.

CWD is highly contagious, and deer can transmit the disease to other deer through direct contact  or through contact with infected saliva, urine or feces. So far, CWD has not been found in humans, but experts recommend against eating venison from an infected animal. In areas where CWD is known to be prevalent, biologists often set up testing stations. It takes a while to get results, but hunters can freeze their meat until test results are known.

More Reading:

USGS: What is chronic wasting disease?

https://www.usgs.gov/faqs/what-chronic-wasting-disease

 

Hemorrhagic Disease

 

 

Hemorrhagic disease infects both deer and livestock. Humans cannot contract these diseases. Two closely related diseases fall under the hemorrhagic category, including epizootic hemorrhagic disease and bluetongue virus.

Both EHD and BTV are viral diseases caused by biting Culicoides midges, also known as no-see-ums or gnats. The virus is not transmitted from deer to deer, but is transmitted when a midge bites an infected animal and then bites an uninfected animal. Disease outbreaks are most common in late summer and early fall, when midges are most abundant. The worst outbreaks tend to occur during hot, dry years when animals have to water around stagnant pools, which are perfect midge breeding grounds. A hard frost kills the insects, ending the disease threat for the season.

Symptoms of hemorrhagic disease include fever, excessive salivation, bruises on the mouth and nose, swelling in the head, neck, lips and tongue and bluish color on the tongue. Deer often appear weak, lethargic and disoriented and lose their wariness around people. They often seek out water to combat fever. Therefore, it’s common to find dead deer near water sources. Once infected, deer show symptoms within two to 10 days and usually die within 36 hours.

EHD occurs annually in the South, but deer in this region have developed antibodies to the virus and mortality rates are relatively low. EHD is becoming more common farther north, where mortality rates are higher because deer haven’t developed antibodies to the disease. In these areas, the disease may take out up to 90% of the whitetails within a localized area. Those that survive develop antibodies to the virus that could be passed along to offspring. Deer that survive EHD often exhibit split or sloughing hooves.

More Reading:

New York State Department of Environmental Conservation: Epizootic Hemorrhagic Disease

https://www.dec.ny.gov/animals/123773.html#:~:text=Epizootic%20Hemorrhagic%20Disease%20(EHD)%20is,deer%20or%20bites%20from%20midges

Potential Diseases and Parasites of White-tailed Deer in Missouri

https://extension.missouri.edu/publications/g9489

 

Cutaneous Fibromas

 

 

Cutaneous fibromas, sometimes called deer warts, are dark-colored nodules found on a deer’s skin, sometimes in clusters (in extreme cases, more than 200 fibromas have been found on a single deer). They are most common on the head and neck, but can grow anywhere on the body. They occur all across the whitetail’s range. Fibromas are caused by a virus that is thought to be transmitted through insect bites. It may be possible for the virus to infect deer through a skin wound as well. They are mostly harmless to deer but can affect vision and movement. In some cases, if a deer receives a skin wound at the site of a fibroma, a secondary bacterial infection may occur.

Once a deer is skinned, you won’t be able to detect any sign of the fibromas and the meat is safe to eat, unless the deer had a secondary bacterial infection, as evidenced by pus at the site of the infection.

More Reading:

Mississippi Wildlife, Fisheries and Parks: Cutaneous Fibromas: A Closer Look (Warts & All)

https://www.mdwfp.com/wildlife-hunting/deer-program/diseases-and-abnormalities/cutaneous-fibromas.aspx

 

Brain Abscess Syndrome

Brain abscess syndrome is a bacterial disease that causes deer to grow abscesses in the brain. Arcanobacterium pyogenesis often the bacteria involved in these infections, although others may cause them as well. A. pyogenes is common on the skin, gums and within the circulatory system of deer. Brain abscesses can develop when bacteria enter a head wound; deer often incur such injuries while sparring or casting antlers. The vast majority of BAS cases occur in adult bucks. The disease occurs throughout the whitetail range and is more prevalent in whitetails than any other species.

Infected deer may look uncoordinated, weak and emaciated. They may display aggression, lack of fear, swollen joints and eyes, and broken antlers. Pus may be found in the eye sockets and pedicles. Hunters shouldn’t eat the meat from deer infected with BAS.

More Reading:

Pennsylvania Game Commission: Bacterial Abscess Syndrome

https://www.pgc.pa.gov/Wildlife/WildlifeHealth/Pages/BrainAbscessSyndrome.aspx#:~:text=Clinical%20Signs,the%20eye%20sockets%20and%20pedicles

 

Dermatophilosis

Dermatophilosis, or rain rot, is a skin disease caused by spore-forming bacteria, typically in wet environments. The spores infect animals through direct contact or can be transmitted by biting insects or ticks. The infected animal develops crusty scabs on the skin and often exhibits extensive hair loss. Scabs may detach and reveal inflamed and/or bleeding skin. Infected animals generally recover, especially with the onset of dry weather, but in severe cases, animals may grow emaciated and die. Deer infected with lice or mange may exhibit similar hair loss.

More Reading:

Pennsylvania Game Commission: Dermatophilosis

https://www.pgc.pa.gov/Wildlife/WildlifeHealth/Pages/Dermatophilosis.aspx

 

Other Parasites

Lumpy jaw is caused by parasitic arterial worms, which dwell in the carotid arteries of deer. The worms reduce blood flow to the jaw, interfering with a deer’s ability to chew. Unchewed food accumulates in the cheek and jaw and the food becomes impacted.

Horseflies pick up arterial worm larvae upon biting an animal. The larvae mature in the horsefly and then move to the fly’s mouth, where they are transmitted to a new host when the fly bites a deer. Worms migrate to the carotid artery. Adults measure 2 1/2 to 5 inches in length. The worms cannot transmit to other animals without the horsefly host.

For some deer, the lump simply goes away over time. For others, however, the impacted food can lead to tooth decay, infections or ruptured skin if the “lump” becomes too large.

More Reading:

National Deer Association: What Causes Deer Food Impactions?

https://deerassociation.com/what-causes-deer-food-impactions/

The American liver fluke is a common white-tailed deer parasite. The flat, oval-shaped trematode is purple or gray and dwells in the liver. It measures 1/2 to 1 inch wide and about 1 to 4 inches long. Hunters can detect it only by cutting into this organ. Often, the deer’s liver forms a fibrous capsule around the fluke. The fluke has a complex life cycle, but simply, deer ingest the young flukes when they cling to vegetation after spending time developing in snails.

Liver flukes are not uncommon in deer, and whitetails display no real negative effects from their presence. Meat is fine to consume from infected individuals, although you may opt to avoid eating the liver.

More Reading:

Michigan Department of Natural Resources: Deer Liver Fluke

https://www.michigan.gov/dnr/managing-resources/wildlife/wildlife-disease/deer-liver-fluke#:~:text=The%20trematode%20frequently%20found%20in,%2C%20phylum%20Platyhelminthes%20(flatworms).

If this list wasn’t enough, many other parasites frequently infect deer, including lungworms, meningeal worms, abdominal worms, larval tapeworms, sarcocystis, nasal bots, muscle worms and large stomach worms. Though unsightly, none of these parasites are particularly harmful to deer, and thoroughly cooked meat from infected deer is safe to eat.

More Reading:

National Deer Association: 10 Weird Parasites That Live Inside Deer

https://deerassociation.com/10-weird-parasites-live-inside-deer

 

 

 

 

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