The value of a closer look when cause of death is known
A closer look helped detect zoonotic pathogens in urban hares.
The life of a wild animal isn’t easy. Find enough food, don’t become food, don’t get injured or killed, reproduce! Are all general rules of survival from day to day. There are many ways to die if you’re a free ranging beast and people working in the field of wildlife diagnostics are trying to understand the cause of death in animals we examine. Sometimes cause of death is already known by the time the animal reaches our lab for necropsy. This may be because the finder witnessed the incident and the cause of death was obvious: for example, striking a window or being hit by a car. We all have mixed feelings about these cases. They are useful for disease surveillance because we can test them for a number of different diseases of interest, like white nose syndrome in bats and highly pathogenic avian influenza in birds. They should be quick, straightforward cases because the cause of death has already been determined. Often, though, they feel like missed opportunities, as budget and time constraints prevent us from looking beyond the obvious. Even when the cause of death is clearly trauma, every wildlife pathologist has a voice in the back of their head that asks, “But why did they become injured? Was there some disease process at work that was slowing them down or affecting their coordination? Maybe I’ll just have a quick look.”
Recently, these “quick looks” have proven valuable in working with several white-tailed jackrabbits submitted to CWHC Western/Northern (CWHC W/N). We commonly receive urban jackrabbits with known cause of death – usually trauma. Their urban lifestyle and unsafe road-crossing habits mean they are often injured by vehicles, and their small size means they are more likely to be picked up by the public when found injured. For many, we swab for relevant diseases and confirm cause of death as expected based on the history provided to us, but for others, a more thorough investigation is needed.
Most notable was a recent case of Tularemia in a white-tailed jackrabbit from Saskatoon. This rabbit was found lethargic and pregnant and taken to the WCVM Small Animal Clinic where it was examined, but died a short time later and was submitted to us. The cause of death was stated as complications from the birth process, but as this is an unusual diagnosis, the pathologist conducted a full necropsy to look for an underlying infectious cause. Several abnormalities were seen during the internal exam including changes to the spleen and lungs, as well as unusual lesions in the trachea. After examining the tissues microscopically the pathologist ordered tests that eventually led to a confirmed diagnosis of Tularemia, the first in Saskatoon since 2017.
Tularemia is caused by the bacteria Francisella tularensis and is transmitted by contact with infected animals, contaminated environments, or through insect bites. It causes severe illness and death in rabbits, hares and rodents, but can infect a number of wild and domestic species. The bacteria also poses a risk to humans, which is especially important when dealing with submissions that are handled by a number of people in the rescue and rehabilitation process before they end up at our lab. Human cases of tularemia are not common in Canada and deaths due to the disease are very rare, but the bacteria can cause severe illness and even death if left untreated.
Another female jackrabbit from Saskatoon was submitted within the same week. This one was found injured and died shortly afterward. On examination, the animal had two fractured hind legs, which could have been the end of the exam, but a closer look revealed changes to the spleen and uterus that prompted tissue collection and further investigation. The animal was found to be infected with Listeria monocytogenes, a zoonotic bacteria that has been making headlines this summer due to human infections caused by contaminated beverages in Canada and contaminated deli meats in the US. Pathologists at CWHC W/N have previously shown this bacterium to be a cause of septicemia and abortion in wild rabbits (Rothenburger et al. 2015)
Both pathogens cause important zoonotic diseases and are thought to affect wildlife populations in some situations. Both could have been overlooked had the cases been discarded after a brief external exam. Of course, in a perfect world we would have the time and funding to do a full workup on every wildlife case but in reality, the triage process is necessary to keep cases moving when time and budgets are limited. We can only hope that our gut might urge us to take a closer look when there is an interesting pathology waiting to be uncovered. In these two cases, a closer look has proven valuable in our understanding of disease-causing agents in urban wildlife.
References:
Jamie L. Rothenburger, Katarina R. Bennett, Lorraine Bryan, Trent K. Bollinger; Septicemic Listeriosis in Wild Hares from Saskatchewan, Canada. J Wildl Dis 1 April 2015; 51 (2): 503–508. doi: https://doi.org/10.7589/2014-06-159
Author: Erin Moffatt, CWHC Western/Northern
