Swollen Muzzle in a White-Tailed Deer.

White-tailed deer are one of the more interesting and challenging species that we have the opportunity to work with. The biggest challenge is often trying to figure out how to get such a large animal to us in Guelph. Our typical method of bringing animals in is in a cooler, this doesn’t really work for an animal of this size. Luckily for us, the Ministry of Natural Resources and Forestry (MNRF) also has a strong interest in monitoring Ontario white-tailed deer populations for disease, so they are often able to find someone to retrieve the deer and deliver it to us. Both CWHC and the MNRF work with hunters on many of these cases as hunters are often a great source in discovering abnormalities in deer. As I mentioned, white-tailed deer are also one of the more interesting animals that we receive and that’s because they often come with some very interesting lesions for us to investigate, which is no different with this deer that was presented to us in early December 2020.

photo: Joe Kosack/Pennsylvania Game Commission

An adult male white-tailed deer was presented to the Ontario-Nunavut region of the Canadian Wildlife Health Cooperative (ON/NU CWHC) with a history of having poor balance while seen walking on a property in London, Ontario. The deer was later found laying down in water unable to get up and appeared to be very weak. The deer was skinny and was reported to have some swelling around the eyes. The police were called and humanely dispatched the deer.

On initial examination of this deer, the first thing that was clear was that this deer was emaciated with no remaining fat stores and reduced overall muscle mass. It was also noted that the left front foot was swollen and there was an open wound that had blood and pus oozing from it. Aside from those findings, one of the other striking features was that the entire upper muzzle was swollen and red, which appeared to be worse on the left side. When the oral cavity was examined, there were some erosions of the lips and cheeks in the most severely affected areas. When the tissue of the muzzle was dissected, there were occasional pockets of pus, but the majority of the tissue was dark red and oozed light red fluid. The lymph nodes of the head were all swollen as well.

Based on these findings a few things were clear. The first is that this deer had been suffering for a while since it would take at least a week or more to become as emaciated as this deer was. Second, the swelling and infection of the left front foot was most likely secondary to a penetrating injury as the sole of the foot did not appear to be involved and there was evidence of an open wound on the front of the foot. Finally, the swelling of the muzzle could suggest a couple of different diseases. One would be a disease entity termed “Bullwinkle disease”, as these deer have a large nose, not unlike the moose character Bullwinkle from the old “The Adventures of Rocky and Bullwinkle” cartoon. Another possibility would be necrobacillosis, which can cause severe necrosis (cell death) of the tissues around the mouth.

Additional testing was required and as we do with all deer presented to us, we first ruled out important zoonotic (diseases that could also cause illnesses in people) and emerging diseases. This deer tested negative for Chronic Wasting Disease and there were no acid fast bacteria to support tuberculosis as a cause for the swollen lymph nodes (this case was not a true tuberculosis suspect as the lesions did not support this disease, but it is something we want to rule out completely before sending samples for testing). Samples from the muzzle and foot were sent for bacterial culture. The sample from the foot grew three different bacteria, but the one in largest numbers was Trueperella pyogenes, which is a common bacteria involved in abscesses in deer, especially those that are the result of some sort of previous trauma or infection in the area (what we often term an opportunistic invader). The muzzle grew a number of different bacteria, but in large numbers (and likely the most important) was Fusobacterium necrophorum, which is the causative agent of necrobacillosis (one of our differentials from above).

Fusobacterium necrophorum is a normal bacterium of the alimentary tract of mammals. However, it can cause disease as an opportunist by invading into the tissue when there has been some sort of damage to the surface. Often these infections affect the head of the animal, but it has been known to cause disease in other parts of the body (predominantly the feet). Disease is most commonly noted in farmed animals; however, disease can occur in any animal with damage to the epithelium and is occasionally noted in free-ranging deer. When the bacteria invade into the underlying tissue, they can cause immense destruction and will often lead to severe cellulitis (inflammation of the tissue) and necrosis (death of the cells in the tissue). Additionally, this amount of damage would likely be extremely painful, which, in our case, may help explain why this deer was so emaciated. Assuming this deer was in a lot of pain as a result of the infection, it should not be a surprise that it would have had trouble eating normally, leading to weight loss over time.

Before ending this, I did want to come back to “Bullwinkle disease” briefly, as it is an interesting disease that we have not yet seen in our white-tailed deer populations in Ontario. This disease has been noted throughout much of the United States since 2002; however, it wasn’t until this past year (Aug. 2020) that researchers isolated a causative agent. Keel et al. examined 27 deer (25 white-tailed deer and 2 mule deer) suffering from this condition and were able to identify a bacterium, Mannheimia granulomatis, as the most likely causative agent of this disease. We finally have an agent to blame for this affliction affecting deer, but I should note something else of interest with Bullwinkle disease. The good news with this disease is that although it looks awful and likely causes pain for these deer, it does not appear to be universally fatal, as there have been reports of deer surviving for years with this disease. However, just as with our deer with necrobacillosis, it would likely prevent affected deer from being able to eat properly, which could lead to weight loss and eventual death in severe cases.

Although Bullwinkle disease has not made its way to Ontario yet, we here at CWHC along with our colleagues at the MNRF will continue to monitor disease populations in the hopes of identifying the diseases that are currently circulating in the population. If you would like to report any sick deer or other wildlife to the MNRF then you can contact them at 1-800-667-1940. Additionally, anyone in Ontario is encouraged to contact the ON/NU region of the CWHC if they find dead wildlife at any time during the year. Our e-mail address is on-nu@cwhc-rcsf.ca and our toll-free phone number is 1-866-673-4781.

Reference: Keel et al. Granulomatous Inflammation of the Muzzle in White-Tailed Deer (Odocoileus virginianus) and Mule Deer (Odocoileus hemionus) Associated With Mannheimia granulomatis. Vet Pathol 57(6):838-844, 2020.

Submitted by:

Brian Stevens , wildlife pathologist ON/NU region

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