A recent study has revealed alarming genetic mutations linked to rodenticide resistance in urban rodents, indicating that controlling these pests in major cities may become increasingly challenging. Conducted by researchers from Rutgers University, the investigation focused on populations of house mice and Norway rats across New York, New Jersey, Pennsylvania, and Washington, D.C.
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The findings, published in the peer-reviewed journal Pest Management Science, highlighted that a significant 84% of house mice sampled carried at least one mutation in the Vkorc1 gene, a genetic marker associated with resistance to anticoagulant rodenticides. In contrast, approximately 35% of Norway rats exhibited similar mutations, but the implications for these rats remain uncertain.
The data for this research was gathered from 147 house mice and 143 Norway rats collected from densely populated urban areas between 2021 and 2025. The study’s co-author, Jin-Jia Yu, a postdoctoral fellow at Rutgers University, commented on the results, stating that the extent of resistance in house mice appears to be more widespread than previously anticipated. Yu noted that while a majority of the house mice sampled carried mutations that are known to confer resistance to rodenticides, the impact of the mutations found in Norway rats has yet to be fully assessed.
In addition to confirming known mutations, the researchers uncovered several previously undocumented genetic variants in both house mice and Norway rats—some of which have never been observed in the United States before. This discovery underlines the evolving nature of these rodents and their adaptability in the face of human attempts to control their populations.
Changlu Wang, another co-author of the study and an extension specialist in the Department of Entomology at Rutgers University, emphasized the importance of addressing the issue of rodent resistance. Wang stated that as resistance to rodenticides increases, it becomes imperative to implement science-driven management strategies that safeguard public health and protect the environment.
Anticoagulant rodenticides, such as warfarin and brodifacoum, operate by disrupting blood clotting processes, leading to fatal internal bleeding. However, these chemicals pose risks not only to the targeted rodent populations but also to non-target wildlife through secondary poisoning. This concern was brought to light following the tragic 2024 death of Flaco, a beloved Eurasian eagle-owl, which was placed in the spotlight after ingesting rodenticides that had been used across New York City.
In light of their findings, the researchers advocate for a multifaceted approach to rodent management rather than a reliance on poison alone. They recommend strategies that include sealing potential entry points to buildings, enhancing sanitation practices, eliminating food sources, and deploying traps. To mitigate the development of rodenticide resistance, the team also suggests rotating the types of rodenticides used in urban pest control efforts.
Yu highlighted the potential benefits of understanding the prevalence and specific distribution of these mutations, as this knowledge can inform pest management professionals and public health agencies to devise more effective control measures for urban rodent populations.
As the resistance issue escalates, understanding and adapting to the evolving genetic landscape of these rodents will be critical for maintaining effective pest control. Urban centres across the United States may need to reconsider their strategies for managing these common pests, balancing the immediate necessity of rodent control with the long-term implications for environmental health and the safety of non-target species.
Continued research into the genetic makeup and behavioural patterns of both house mice and Norway rats will be paramount in developing sustainable management practices in the face of increasing rodenticide resistance.