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Earlier this summer, the Canadian Wildlife Health Cooperative, with assistance from Prairie Diagnostic Services and the Public Health Agency of Canada’s National Microbiology Laboratory, made the diagnosis of tularemia in both a white-tailed jackrabbit and a red squirrel found in residential parks within the Saskatoon city limits.

These cases were notable for a couple of reasons. First, tularemia is a zoonotic disease, which means it can be transmitted to humans. This was the first time we had diagnosed the disease in urban wildlife where the potential for contact with people is high. As well, the rabbit was initially submitted to a rehabilitation facility with the suspicion that it had been hit by a car, resulting in further contact with humans. Second, although we diagnose tularemia occasionally in muskrat and beaver, and a widespread die-off of deer mice in southern Saskatchewan in 2005 was determined to be due to tularemia, this is the first time we have diagnosed the disease in a white-tailed jackrabbit.

In years past, when commercial trapping of muskrat and beaver and the hunting of rabbits was much more common, tularemia in people was a more frequent occurrence. Although readily treated with antibiotics, prior to their discovery and widespread
availability, infection with tularemia could be fatal. While tularemia fatalities today are very rare, people can be hospitalized with the disease.

Tularemia is caused by the bacterium Francisella tularensis. This bacterium has a very broad host range, which includes mammals,
birds, amphibians, and invertebrates, but it is primarily a disease of lagomorphs (rabbits and hares) and rodents. In North America, there are two subspecies: tularensis (also known as Type A) and palaearctica (also known as Type B or holarctica). In western and northern Canada, Type B is the most common subtype isolated, typically in muskrat and beaver, but it was also responsible for the deer mouse die-off in Saskatchewan, and was the subspecies found in the jackrabbit from Saskatoon. Fortunately, the holarctic, or Type B strain, is less serious in people than Type A. Type A tularemia is more often associated
with rabbits and hares and is more common in eastern North America.

Tularemia is highly infectious and can be transmitted by the bite of blood-feeding insects (mosquitoes, fleas, deer flies, and ticks), contact with tissues of an infected animal, inhalation of infectious particles, or by ingestion of contaminated water or meat. In a publication from the early 1950s, higher rates of tularemia in rabbit hunters in Illinois and Minnesota were associated with early hunting seasons when insect vectors were still abundant prior to freezing temperatures.

       

In Canada, human cases are most often seen in trappers. Occasionally there are reports of grounds-keepers becoming infected, and in at least one case, it was thought to have been associated with a person running over a tularemia-infected carcass with a lawn-mower, aerosolizing the bacteria which was then subsequently inhaled. Another interesting case from the 1970s involved a veterinarian at the Assiniboine Park Zoo in Winnipeg who became infected after being bitten by a monkey that was receiving treatment for tularemia. Some monkeys appeared to have become infected from contact with ground squirrels in the exhibit (which were subsequently found to be infected with Francisella tularensis) and several monkeys in the collection died.

Tularemia in people can take several forms, depending on the route of exposure. If the bacterium is inhaled, coughing or difficulty in breathing can occur (pneumonic form). If there is a bite or skin exposure, ulcers can develop, along with swollen and painful draining lymph nodes (ulceroglandular form). Sore throat or abdominal pain can occur with ingestion of the bacterium (digestive
form). If the disease becomes more widespread in the body, people can develop fever and chills with muscle and joint pain (typhoidal form). Given the range of symptoms, this disease may be misdiagnosed and is likely under-reported. Prompt and proper diagnosis with appropriate antibiotic treatment can prevent development of more severe disease.

On a final note, August 2017 media reports from the interior and southcentral region of Alaska indicate there has been an increase in the number of cases of tularemia in dogs and cats, some of them fatal. Contact with infected snowshoe hares is thought to be the source of disease in many of these cases.

People should not be unduly worried about tularemia, as its diagnosis is relatively uncommon in people and pets, but should be aware that this is a potential cause of disease, especially if there is a high level of contact with lagomorphs and rodents, either through work or recreation

Author: Trent K. Bollinger, DVM,
Canadian Cooperative Wildlife Health Centre,
Western College of Veterinary Medicine.
Trent is a regular contributor to WCGW.



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