New Research Finds Widespread Rodenticide Resistance in House Mice in Northeastern U.S.

NEW BRUNSWICK, N.J. — A new Rutgers University study found that many house mice populations in major Northeastern cities carry genetic mutations linked to resistance against commonly used anticoagulant rodenticides, raising concerns about the long-term effectiveness of rodent control methods and potential environmental impacts.

Researchers analyzed house mice and Norway rats collected from urban areas in New York, New Jersey, Pennsylvania and Washington, D.C. The study focused on changes in a gene called Vkorc1, which is known to help rodents survive exposure to anticoagulant rodenticides.

The researchers found that 84% of house mice tested carried at least one genetic mutation associated with rodenticide resistance. About 69% carried mutations already known to reduce the effectiveness of some widely used rodenticides.

By comparison, Norway rats showed far fewer resistance-related mutations.

“Our findings suggest that resistance to anticoagulant rodenticides is now very common in house mice in the Northeast,” said Changlu Wang, a professor at Rutgers University and lead author of the study. “This means relying only on anticoagulant rodenticides may no longer be enough for effective rodent control.”

The study identified several important mutations in mice, including two that had never before been documented in house mice or in the common house mouse subspecies found in the United States. Researchers also discovered a previously unknown mutation in Norway rats.

Anticoagulant rodenticides remain one of the most widely used tools for controlling rodents in homes and cities. However, researchers say repeated use of the same chemicals may encourage resistant rodents to survive and reproduce, making infestations harder to control over time. The study also highlights broader environmental issues with rodenticides, including concerns about harming non-targets and long-term persistence in the environment.

Researchers recommend that pest control programs place greater emphasis on integrated pest management strategies, including sealing entry points, improving sanitation, reducing food sources and using traps alongside limited and carefully managed rodenticide use.

The study examined 147 house mice and 143 Norway rats collected between 2021 and 2025 from urban residential areas, including New York City, Philadelphia and Washington, D.C.

The research was supported by the U.S. Department of Agriculture, the U.S. Department of Housing and Urban Development, the National Science Foundation and the Northeastern Integrated Pest Management Center.

The study was published in the journal Pest Management Science.