Urban rat migration reveals hidden ways to spread deadly diseases

A seminal six-year study that tracks populations of Boston rats found how these urban rodents transport and maintain persistent strains of potentially deadly bacteria across urban communities, providing public health officials with important insights to prevent disease outbreaks.

Researchers at Tufts University, Northern Arizona University, the USDA and the Centers for Disease Control and Prevention collaborated to map how rat movement patterns affect the spread of Leptospira bacteria – an important finding on urban health management in cities around the world.

Tracking disease transmission through rat migration

This comprehensive study, published in PLO, overlooked tropical diseases, analyzed DNA from 328 rat kidney samples collected at 17 sites in Boston between 2016 and 2022. The researchers found that nearly 18% of rats carry leptospirosis bacteria, causing lean meat – a type of urination caused by urine or causing severe death in people.

“The main method to obtain a complete genomic sequence of a virus or bacteria is to cultivate it, in this case, which is a challenge because leptospira is considered a picky organism,” said Marieke Rosenbaum, assistant professor of veterinary medicine at Tufts Cummings. “It has specific requirements for temperature, pH, and nutrients. However, our USDA collaborators not only cultivate bacteria from fresh rodent kidneys, but have never been reported in the literature before to obtain isolates.”

This breakthrough in laboratory technology allowed researchers to perform detailed genetic analysis of different Leptospira strains, revealing surprisingly stable geographic patterns throughout the city.

Different rat communities maintain unique bacterial strains

The study showed that Boston rats formed different genetic communities that remained largely separate from each other, with specific leptospirosis strains in these independent populations persisting for years. For example, the average Boston rat has maintained the same leptospira strain for years – a strain that is genetically different from those in other communities.

What factors separate these rat populations? The study identified several key obstacles:

• Large multi-lane roads effectively prevent rat migration between communities
• Rats usually need to travel more than 600 meters (about 1/3 mile) to encounter genetically different rat populations
• Green corridors and parks are migration roads for mouse movement
• Construction projects destroy established rat territory, potentially forcing immigration

From rats to humans: Tracking pathways of disease

Perhaps the most shocking is the discovery that directly links human-induced cases to rats in 2018. Using advanced genome sequencing techniques, the researchers found that bacterial strains from human patients were nearly the same as those isolated from the same location in Boston.

“This is very strong evidence that the root cause of human cases is mice,” Rosenbaum said.

Although human cases of leptospirosis remain relatively rare in temperate areas such as Boston, the disease represents a major health problem in the tropical regions. Climate change may expand the geographical scope of the disease, making these findings increasingly relevant to public health programs.

Rethinking urban pest control strategies

This study’s insight into rat migration patterns challenged conventional methods to control pests. Simply extinct rats in one area without understanding population dynamics may lead infected rats to new places, thus spreading the disease more widely.

“Extinction is unrealistic, but I think it is really helpful to better understand how different pest control interventions affect rat migration and the spread of pathogens in rat populations,” Rosenbaum noted.

Dave Wagner, a professor at the School of Pathogens and Microbiology at Northern Arizona University, emphasized the importance of new genetic tools developed during the research period: “The new genetic tools we develop and use in this study are the real game rules of leptospiration research for leptospiration because we can now use the power of the entire genome to find correlations to find correlations, which is impossible.”

As global efforts face the rat population and the public health challenges they raise, this study provides a roadmap for targeted intervention strategies. By understanding how rats move in urban environments and track specific pathogens they carry, public health officials may be able to develop more effective ways to protect human health while addressing rodent infestations.

The findings suggest that future urban planning may consider how infrastructure developments from roads to parks affect rat immigration patterns and potential disease transmission, an often overlooked aspect of public health management in densely populated urban areas.