Researchers say sanitation and blocked entry points may become more important as genetic resistance spreads among urban mice.
NEW BRUNSWICK, N.J. — Cities may need to rely less heavily on poison alone to control rodents after Rutgers University researchers found widespread genetic mutations associated with rodenticide resistance in house mice from several Northeastern metropolitan areas.
The study adds scientific evidence to concerns raised by pest management workers who have reported recurring infestations despite repeated chemical treatments. Researchers said the findings support an integrated approach that combines sanitation, building maintenance, habitat changes, traps and carefully chosen rodenticides instead of depending on one method.
Rutgers researchers analyzed 147 house mice and 143 Norway rats collected from urban areas in New York, New Jersey, Pennsylvania and Washington, D.C. They found that 84% of the mice carried at least one mutation in the Vkorc1 gene, which has been linked to resistance against anticoagulant rodenticides.
Nearly 70% of the mice carried mutations already known to help the animals survive commonly used poisons. About 35% of the Norway rats carried mutations in the same gene, although scientists have not determined whether most of the rat variants provide meaningful protection.
The distinction is important for local pest control decisions. A mutation associated with resistance in one species may not have the same effect in another, and a genetic test alone does not show that every chemical treatment will fail. Researchers said more testing is needed to connect particular mutations with actual survival after exposure.
Still, the high rate of known resistance mutations in mice suggests that repeated use of the same poisons may become less dependable in some neighborhoods. Rodents that survive treatment can reproduce and pass helpful traits to their offspring, allowing resistance to become more common over time.
Changlu Wang, an extension specialist in the Rutgers Department of Entomology and a co-author of the study, said rodent control has consequences beyond the immediate nuisance of an infestation. Rodents can contaminate food, damage buildings and infrastructure, and carry diseases and parasites.
“As resistance becomes more common, it becomes even more important to use science-based management strategies that protect both public health and the environment,” Wang said.
Those strategies include removing accessible food and water, keeping waste contained, closing gaps that allow rodents into buildings, reducing shelter around properties and using traps where appropriate. Researchers said chemical controls can remain part of a management program, but they should not be treated as the only response.
Limiting unnecessary poison use may also reduce risks to animals that were not targeted. Predators and scavengers can be exposed when they eat rodents carrying rodenticide residues. A treatment that fails to kill a resistant rodent could still leave poison in the food chain.
Jin-Jia Yu, a Rutgers postdoctoral fellow and the study’s first author, said information about where resistance occurs could help public health agencies and pest professionals make better decisions. Researchers are continuing to examine how common the mutations are and whether newly identified variants affect the performance of specific rodenticides.
Author note: Last updated July 24, 2026.