Chelsea Himsworth, left, and U of S student Jamie Rothenburger examine a wild rat for potential diseases (photo: Victoria Chang).

Student studies diseases of wild urban rats

Vancouver Rat Project is the first study in Canada to evaluate the health of wild rats.

Wild urban rats carry bacteria and viruses that can pose a significant health risk to people, yet very little is known about them in Canada.

That's why I am studying the natural diseases of this often despised mammal, one of the most successful invasive species. The Vancouver Rat Project, of which I am a team member, is the first study in Canada to systematically evaluate the health of wild rats. While diseases of laboratory rats have been extensively studied, little is known about those in wild rats.

"In cities, rats and people live in very close contact," said University of Saskatchewan veterinary pathologist Ted Leighton, my supervisor on the project.

"Rats have been important reservoirs of human diseases, including plague. Surprisingly, modern science and public health have paid very little attention to urban rats. This leaves a big gap in our understanding of potential public health threats now and in the future."

To investigate rat diseases, I partnered with veterinary pathologist Chelsea Himsworth, a U of S graduate who is doing a PhD at the University of British Columbia and leads the project with funding from the Canadian Institutes of Health Research, the City of Vancouver, the B.C. Centre for Disease Control and the Urban Health Research Initiative.

"We probably know more about natural disease in animals like elephants and polar bears, which are animals that few of us have actually seen, than we do about rats," Himsworth said.

"Understanding how diseases work in rat populations is key to understanding the risk of disease transmission between rats and humans and to developing informed and effective strategies to monitor and mitigate that risk."

This three-part study aims to better identify rat habitats, estimate their population, evaluate their natural diseases, test for viruses and bacteria that people can get from rats and evaluate human exposure to rat-associated infectious diseases.

Though Saskatchewan is known for its crop-destroying rat infestations, Vancouver's rat-infested inner-city area with its at-risk populations was a natural starting place for an urban rat study.

Starting last fall, rats in Vancouver's Downtown Eastside were systematically trapped, block by block, using traps baited with peanut butter and bacon fat. Most were Norway rats, the most successful colonizer.

Stock image of rat

The 720 captured rats were given an anesthetic drug, had a blood sample collected and were humanely euthanized. Roughly 50 samples were collected from each rat for additional testing.

An unexpected finding was that one-third of the rats were visibly unhealthy. This suggests natural disease may play a more important role in keeping populations under control than previously thought.

Over the next two years, we will test samples for a variety of bacteria and viruses that could spread from rats to people. These include Salmonella, Seoul hantavirus and leptospirosis, an infectious bacterial disease that can lead to kidney and liver failure in humans. We are also testing for antibiotic-resistant bacteria, the so-called superbugs. People from the area will be tested for exposure to these pathogens.

Studies like this may be useful in guiding policy such as the Saskatchewan Provincial Rat Eradication Program, which began in 2010 and has the goal of eliminating rats from this province.

As a Saskatchewan native, it was a culture shock to encounter Vancouver's Downtown Eastside with its rampant drug use, grinding poverty and homelessness. However, I was impressed by the community support for this project.

During the next six months, I will examine hundreds of microscope slides in search of microscopic disease such as inflammation and parasites in rat tissues.

Jamie Rothenburger is a veterinarian doing her master's at the U of S Western College of Veterinary Medicine, and a writer with the U of S research communications program.

This article first ran as part of the 2012 Young Innovators series, an initiative of the U of S Research Communications office in partnership with the Saskatoon StarPhoenix.

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