Rats are well known for carrying diseases. And as they migrate in cities, they spread bacteria that could be life-threatening to humans, according to a six-year study co-authored by Nate Stone, a Ph.D. student turned research scientist at NAU’s Pathogen & Microbiome Institute, and Dave Wagner, PMI’s executive director. The pair worked on the research alongside colleagues at NAU, Tufts University, the United States Department of Agriculture and the Centers for Disease Control and Prevention.
The study found that urban rats carry a type of bacteria that causes leptospirosis, a disease that sometimes damages the liver and kidneys and could lead to death in humans. The disease-causing bacteria are spread through rats’ urine in soil, water and other parts of urban environments, where they can become a source of infection and contamination for humans, dogs and other species. The bacteria are most common in tropical regions—but rising temperatures from climate change could cause them to become more prevalent.
Researchers found that leptospirosis persists in Boston rat populations, and different strains of the bacteria move around the city as groups of rats migrate. In addition, the scientists’ genetic analysis of a 2018 human leptospirosis case in Boston strongly suggests a link to rats as the source.
The study was recently published in PLOS Neglected Tropical Diseases.
Researchers undertook the study in partnership with Boston’s Inspectional Services Department, tracking rats at 17 different sites from 2016 to 2022, testing more than 300 of them for leptospirosis and using advanced molecular techniques to identify different strains of the disease. They found that 59 of the rats at 12 of the sites tested 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,” said Marieke Rosenbaum, senior author of the study and an assistant professor in the Department of Infectious Disease and Global Health at Cummings School of Veterinary Medicine at Tufts University. “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, Stone, Wagner and a dozen of their PMI colleagues used targeted DNA capture and amplification to pick out and enhance leptospirosis DNA in the samples, which gave the researchers a rich set of fine-scale genomic information about the isolates.
“The new genetic 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,” Wagner said.
Rosenbaum said that being able to see how each strain is related helped them understand exactly how the bacteria were getting transmitted between groups of rats in Boston. Their findings could help guide rat control and human leptospirosis mitigation in cities and could also inspire further research into how city control programs either prevent or encourage the spread of bacteria.
“Extermination is not realistic,” Rosenbaum said. “I think a better understanding of how the different pest control interventions are impacting rat migrations and transmission of pathogens among the rat population would be really helpful.”
NAU researchers who contributed to the research included Ryelan McDonough, Reanna Bourgeois, Rebecca Ballard, Natalie Thornton, Marianece Nuttall, Ryann Whealy, Skylar Timm, Alexander Roberts, Viacheslav Fofanov, Talima Pearson, Jason Sahl and Joseph Busch from PMI and Tara Nurstenau from the School of Informatics, Computing, and Cyber Systems.
This project was supported by the National Institutes of Health under award numbers R01AI172924 and K-24 AI 106822 (Institute of Allergy and Infectious Diseases); K08ES035460 (Institute of Environmental Health Sciences); and KL2TR002545 (National Center for Advancing Translational Sciences). This research was supported in part by an appointment to the Animal and Plant Health Inspection Service (APHIS) Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and the U.S. Department of Agriculture (USDA). ORISE is managed by ORAU under DOE contract number DE-SC0014664. Complete information on authors, methodology, funders and conflicts of interest is available in the published paper.
Jill Kimball | NAU Communications
(928) 523-2282 | jill.kimball@nau.edu