hey are our upstairs neighbors whose late-night antics keep us awake. They commute with us on city subways. And we run into them when taking out the trash.
We’re talking urban rats, of course.
But despite how commonplace rats are in cities around the world, they remain in many ways mysterious, including in the potential threat they pose to public health, experts say.
To combat that, a trio of scientists outlined on Thursday in the journal Frontiers in Public Health step-by-step recommendations for how they say public health officials should capture rats, implant them with microchips, test them for pathogens, and track their activity. The methods were developed and tested with rats in New York City, to whom the researchers assigned names like Stumpy (who had lost part of his tail) and Christine, a tiny yet aggressive female.
“There’s not a lot of research being done with rodents, and because of that, we don’t have a lot of information about the pathogens they harbor,” said Michael Parsons, the report’s lead author and a chemical and behavioral ecologist.
Rats — and rodents more broadly — aren’t responsible for nearly as many disease cases or deaths as, say, mosquitoes. But they can transmit fevers, a type of meningitis, and, yes, plague. The diseases are spread through bites and scratches, pathogens in the animals’ feces and urine, and via fleas. (People are not susceptible to all pathogens that rats harbor.)
But no one has a good measure for just how dangerous rodents are to human health, experts say. Many infections spread by them might not be diagnosed, and if they are, they might not be investigated to determine if they have rodent roots.
“Rodent-borne pathogens quite possibly make a lot of people ill, but (the cases) may rarely be diagnosed,” said James Childs, an infectious disease expert at the Yale School of Public Health. “It’s very hard for anyone to even estimate the burden of rat-borne disease in the United States or elsewhere.”
Rat researchers also say there are major gaps in our understanding of all the pathogens rats might harbor. A 2014 paper on New York City rats identified what the authors called “a vast diversity of microbes that may affect human health,” leading them to call for “increased surveillance and awareness of the disease risks associated with urban rodent infestation.”
And because rats can pick up so many different pathogens, they “may also serve as mixing bowls, providing an environment in which pathogens may interact and even exchange genes that promote resistance to certain drugs,” Kaylee Byers and Michael Lee, graduate students at the University of British Columbia who study rats and public health, wrote in an email.
“Effectively, rats can act as sponges, picking up microbes in the environment … though the role of rats in transmitting these microbes back to people is uncertain,” they wrote.
We also don’t know much about what rats do all day and night, said Parsons, a scholar-in-residence at Hofstra University. (We can only hope they’re whipping up our favorite childhood dish or training ninja turtles).
When rats go viral — as in Internet famous, not infectious — that can lead to false generalizations about rat behavior, Parsons said. Sure, that one rat may have liked New York’s famous pizza so much that he tried to take his leftovers with him, but he may have been unusually brave.
Parsons said he is not trying to stir unnecessary fear of our fellow city dwellers. But he suggested that getting ahead of the problem by surveying what rats could do makes more sense than scrambling if a problem emerges.
“Instead of sampling animals periodically, on a punctuated basis,” Parsons said, “we need to implement something on a continual basis.”
The New York City Department of Health and Mental Hygiene did not respond to questions about its rat surveillance program and what it thought of the new paper. In 2015, the city’s rat budget got a $2.9 million boost and its program has about 170 people on staff, including exterminators and scientists.
The quality of rat control varies city by city, but Childs, the Yale expert, said New York is one of the more proactive (he also cited New Orleans as a standout).
The paper, which Parsons wrote with a fellow Hofstra scientist and a medical entomologist from an extermination company, outlines the steps the researchers developed to trap rats and then monitor them.
They first seeded cages with rat pheromones to lure the rodents. The researchers anesthetized the captured rats, collected bodily fluid and fecal samples, gathered parasites from fur, and inserted a microchip about the size of a grain of rice between their shoulders.
The paper also offered advice for finding rats: a place in a crowded area but where you can conduct the research discretely — property owners won’t want to help you out if you broadcast they have rats.
After being released, the rats were drawn back to sensors that weighed them, providing regular insights into their health. The researchers also recaptured some rats for tests to see if pathogen levels changed over time.
Byers and Lee,who were not involved with the new paper, said the protocol would be useful for tracking diseases, but that it can be expensive and labor- and time-intensive for cities to launch such programs.
“Depending on the number of pathogens [and rats] a municipality is interested in testing, the cost of diagnostic testing alone can quickly add up,” they wrote in an email.
They added that luring rats to the same sensors could lead to interaction between infected rats and uninfected rats, and that the sensors would need to be sanitized to avoid becoming an infection source.
Parsons said he is not dead set on the methods outlined in the paper, but that he hopes public health officials see that they should be thinking about this issue.
“Maybe this isn’t the approach,” he said. “We’re just trying to start the conversation.”