Urban Rats Spread Deadly Bacteria as They Migrate, Study Finds


Urban rats spread a deadly bacteria as they migrate within cities that can be the source of a potentially life-threatening disease in humans, according to a six-year study by Tufts University researchers and their collaborators that also discovered a novel technique for testing rat kidneys. 

Leptospirosis is a disease caused by a type of bacteria often found in rats. It’s spread through their urine into soil, water, or elsewhere in the environment, where it becomes a source of infection and contamination for humans, dogs, and other species. While it’s prevalent worldwide, it’s more common in tropical regions, though a changing climate means it could become more common in colder regions as they warm. 

In Boston, leptospirosis persists in local rat populations, and different strains of the bacteria move around the city as groups of rats migrate, according to a new study by Marieke Rosenbaum, M.P.H., D.V.M., assistant professor in the Department of Infectious Disease and Global Health at Cummings School of Veterinary Medicine at Tufts University, along with co-authors at Northern Arizona University (NAU), the United States Department of Agriculture (USDA), and the Centers for Disease Control and Prevention (CDC). In addition, their genetic analysis of a 2018 human leptospirosis case in Boston strongly suggests a link to rats as the source.

The paper, published recently in the journal PLOS Neglected Tropical Diseases, is the latest work conducted by Rosenbaum and collaborators as part of the Boston Urban Rat Study, a research group investigating whether rats in Boston carry pathogens that pose a risk to public health. For this study, she joined forces with the City of Boston’s Inspectional Services Department and other groups throughout the city to track rats from 2016 to 2022 and test rats for leptospirosis. She and researchers then employed advanced molecular techniques to figure out exactly what type of leptospirosis was present. The researchers analyzed DNA from 328 rat kidney samples collected from 17 sites in Boston, and 59 rats representing 12 of 17 sites were positive for Leptospira bacteria.

“The primary way to get a full genomic sequence of a virus or bacteria is to culture it, which was a challenge in this case because Leptospira is considered a fastidious organism,” says Rosenbaum. “It has specific requirements for temperature, pH, and nutrients. But our USDA collaborators cultured the bacteria from not only fresh but also frozen rodent kidneys, which has never been reported in the literature before, to get isolates.”

From there, the Northern Arizona University collaborators at the Pathogen & Microbiome Institute (PMI) used targeted DNA capture and amplification to pick out and enhance leptospirosis DNA in the samples, which resulted in a lot of fine-scale genomic information about the isolates. 

“The new genetic and tools that we developed and used in this study are real game changers for leptospirosis research, as we can now use the power of the whole genome to look for relatedness among samples, something that just wasn’t possible before,” said Dave Wagner, Ph.D., professor of biological sciences and executive director of the PMI at NAU.

“Because we were able to do the culturing and the sequencing, we were able to look more closely at how the different strains of leptospirosis are related, which helps us understand how the bacteria are getting transmitted between rats and rat populations in the city,” Rosenbaum says. 

The researchers hope their findings will help guide rat control and human leptospirosis mitigation efforts in urban settings.

Source: https://www.eurekalert.org/news-releases/1082653 

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