Project Tracks Urban Rats’ Health Risks to Humans

They’re blamed for spreading the Black Death in medieval times and other modern-day scourges such as leptospirosis and rat-bite fever.

But even though rats are thriving in cities around the world, current data about this species is scarce, says Dr. Chelsea Himsworth, regional director for CWHC in British Columbia.

“Really, we started out knowing pretty much nothing about Canadian rats or the health risk that they might pose to citizens,” says Himsworth, who is also director of the Vancouver Rat Project.

Now in its seventh year, the project speaks to one of the CWHC’s current focuses: urban wildlife. With the majority of the world’s population now living in cities, people are more likely to come into contact with urban wildlife than any other type.

Kaylee Byers and Michael Lee with a fresh caught rat as part of the Vancouver rat project.


That’s why Himsworth has set out to discover what rat populations in Canadian cities look like: how many there are, how they are distributed and how they behave.

She’s also seeking to discover the array of organisms they can carry. Using modern knowledge and methodologies, her team is looking at pathogens known from past research as well as the potential for rats to be the source of new health risks.

From the project’s first phase, understanding rats and risk, Himsworth learned that risk varies from one rat population to another. Not all populations carry the same set of diseases, and diseases can be very unevenly distributed.

Dr. Ted Leighton assists in identifying the pathogens carried by rats captured in the Vancouver rat project.


Now she wants to further understand why rats pose a health risk, and why some populations are more risky than others.

One graduate student is investigating how rats in a population are related to each other, and whether disease organisms are more likely to be transmitted within families or between families.

Another student is looking at whether the urban environment can be engineered to make rats less diseased.

A third student is studying what happens when people attempt to indiscriminately trap and poison rats. Himsworth says some control efforts may actually make rats more dangerous than if they had been left alone.

“We know from other species that when you disturb an established family group, you can have really unpredictable impacts on the diseases in that group,” Himsworth explains. “And no species is more disturbed than rats.”

As well, there are many questions on the human side of the equation. What are the factors that make people more prone to being exposed to rats? Are there certain behaviours that put them at higher risk? Are people in fact contracting diseases? What is the psychological impact of being forced to live in a rat-infested environment?

The answers to these questions will help health officials predict health threats related to rat populations and learn how to monitor the species and mitigate their impact on people, Himsworth said.

Article produced by Kathy Fitzpatrick

Kathy Fitzpatrick is a freelance journalist in Saskatoon. Born in Manitoba, she has spent close to four decades working in media — including radio, television, print and digital.

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