If you live in a major city, chances are you’ve seen rats scurrying around dumpsters or along alleyways. Urban rats are found around the world, and wherever they go, people work to get rid of them — and for good reason. Rats are infamous for their ability to carry a number of “pathogens,” or disease-causing organisms. They can also infest our homes, damaging infrastructure and keeping us up at night. But what if our approaches to pest control actually increase some rat-associated risks?
Who you gonna call?
Let’s say you wake up to find a few rats living in your home. What happens next? You might call the city to report the infestation (in Vancouver you can call 3–1–1 to report rat and mouse issues), but you’ll likely find that controlling those rats is left up to you. At this point, you may choose to hire a pest control professional, or go-it-alone. Pest control professionals will survey your property to identify sources of the infestation and can help identify next steps in preventing additional rats from entering the premises. Whether you hire professionals or address the issue yourself, the approach will largely focus on removing rats, most often lethally. So you’ve removed the rats, problem solved right?
New rats on the block
While you may succeed in removing rats from your property, it is likely that there will be other rats waiting to move in and set up shop. For my PhD research, I worked with the Vancouver Rat Project to understand the extent to which rats move. Over the course of two years of rat trapping in Vancouver’s Downtown Eastside, we have found that rats are often not restricted to a single property. Because related rats can be distributed across an entire city block or extend across several adjacent blocks, clearing your house or property may not be enough. Relatives of the rats on your property may be just across the fence or alley, infesting your neighbour’s backyard. Many trap-removal studies that use baiting to assess the success of rat removal have found that following a pest-control campaign, any rats left remaining can rapidly reproduce and, voila, you’re back at square one.
Round up all the rats? It’s not so simple
Not only are methods focused solely on removal often ineffective in the long-term, but they can potentially increase rat-associated health risks. In 2016, we enacted an eight-month field study in Vancouver’s Downtown Eastside where we caught and tested rats for a number of pathogens known to cause disease in people. One of these pathogens was Leptospira, a bacterium shed into the environment in rat urine. Leptospira is one of the leading causes of disease spread from animals to people worldwide. People can become ill if they come into contact with this bacterium via cuts or abrasions on their skin or through their mucous membranes (mouth, nose, eyes).
We found that after a pest-control intervention, rats were more likely to carry Leptospira than they were before pest control. This increase in disease-carrying rats only occurred in blocks where a pest control intervention was done. Because Leptospira is spread among rats via contact with other rats and their urine, we believe removing individuals from a population could change normal patterns of social interactions among rats. Removing an individual at the top of the social hierarchy (dominant) may result in a re-negotiating of social structure which results in increased aggression among rats which, in turn, increases pathogen spread. Pest control could actually increase the number of rats carrying a disease-causing bacterium and therefore increase your risks of coming into contact with a pathogen-carrying rat.
It’s a marathon
Although science is showing us how our current rat-control approaches can leave people vulnerable to future infestations, it’s also guiding the way for new control techniques. Genetic work can be used to determine the scale needed for rat control to be effective. If a group of closely related rats spans three city blocks, then management efforts should consider encompassing all of those blocks. We also know that short-term, one-and-done approaches to pest control lead to re-infestation, so management must be proactive and ongoing. There is a growing emphasis on long-term environmental mitigation programs that focus on reducing rat’s access to food and areas to burrow which, with time, can reduce the ability of an area to support rat populations.
Perhaps we should change our focus altogether. Eradication as the sole aim of a rat control program is likely to be met with disappointment. Rats adapt quickly, reproduce rapidly and are very resistant to most of the pest control approaches we’ve thrown at them. Instead, what if we consider rats not as invaders, but as a part of cities?
By viewing rats as part of the urban ecosystem, we can manage the environmental conditions which make areas particularly vulnerable to rats, instead of focusing on the rats themselves. In Vancouver’s Downtown Eastside, rat encounters are common in single room occupancy hotels, where ageing infrastructure allows rats to move easily between rooms and through hallways. Using an ecosystem approach, rat management could involve improving access to and quality of housing in the Downtown Eastside instead of solely focusing on baiting and trapping. This shift would improve the rat-resiliency of neighbourhoods and cities, but requires strategic, long-term investment.
The science is telling us that our current approaches are not working. Are we ready to listen?