Remember the 2008 outbreak of listeria infections in people associated with contaminated deli meat?
The bacterium Listeria monocytogenes caused 20 deaths in one of the most serious outbreaks of food-borne illness in Canadian history.
Along with salmonella and campylobacter, listeria is often listed among the top causes of food-borne illness.
The same bacteria can also be deadly in wild hares, but presumably they pick up the bacteria from food sources other than deli meat.
In 2012 and 2013, concerned citizens found two jack rabbits, which scientists classify as hare species, and a snowshoe hare in the Saskatoon area. They were behaving abnormally and were quite ill, so their rescuers took them to the Western College of Veterinary Medicine’s Veterinary Medical Centre for examination.
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Veterinarians determined treatment was not possible because of the seriousness of the hares’ illness and decided to euthanize them. They submitted the hares to the Canadian Wildlife Health Co-operative’s western-northern region for an autopsy, where they were diagnosed with this unusual cause of illness.
An article describing our findings was published in the April 2015 issue of the Journal of Wildlife Diseases.
The hares were mature females with severe uterine infections. This infection had caused such advanced inflammation and tissue damage in the uterus that the listeria bacteria spread within the body to other organs, causing grave illness.
You may be wondering why I would get so interested in a few hares:
- This is the first time listeriosis has been described in hares from western North America. Researchers reported a few cases in the 1950s in Newfoundland and in European brown hares, which are related to North American hares. This finding contributes to the understanding of wild hare diseases in our neck of the woods.
- It is possible this is an emerging disease resulting from some underlying reason for hares to become ill. Underlying contributors to disease in wildlife include habitat loss, climate change, environmental toxins and invasive species. None of these were obvious contributors to these hares’ illness. It is more likely that listeriosis is rare and that people noticed these hares because they were in cities. Sick or dead wildlife are more difficult for people to detect in rural or natural environments.
- There seems to be something special about listeria infection in hares and rabbits. Unlike cattle, sheep and goats, which get brainstem infections, pregnant female hares and rabbits are particularly susceptible to uterus infections. In laboratory rabbits, researchers could induce infection only in pregnant females. Males and non-pregnant females were resistant. It’s unclear how listeria invades the uterus and causes systemic illness only in pregnant females.
Because this is the first report, we don’t yet understand how widespread it is and how these animals become infected.
Listeria is an environmental bacteria and is not transmissible between animals, which means the risk of spread to people and domestic animals is likely low. Hare hunters and trappers should take care to avoid consuming meat from sick animals and practice appropriate meat hygiene when skinning and preparing carcasses.
People who find sick, injured or dead wild animals should contact the provincial and territorial environment ministries. The CWHC supports these agencies by providing diagnostic and investigative services to determine the cause of death or illness and their significance for conservation, public health and agriculture.
The CWHC website at www.cwhc-rcsf.ca is provides good information on issues of wildlife health.
It is through reported cases such as these hares that researchers can describe and document new diseases in wildlife.
