Scientists have identified disturbing genetic mutations in mice and rats residing in major U.S. cities, rendering them increasingly resistant to common poisons and raising concerns about escalating pest control challenges and public health risks.
A study by researchers at Rutgers University in New Jersey revealed that a substantial majority of house mice and brown rats tested in New York, New Jersey, Pennsylvania, and Washington D.C. exhibit genetic alterations in the Vkorc1 gene, which affects the efficacy of rodenticides.
Of nearly 300 rodents examined, more than 69 percent carried additional genetic mutations previously linked to immunity against common exterminator poisons. The smaller house mouse, which measures between two and four inches and can navigate tight spaces, displayed more significant changes, indicating a potentially faster mutation rate compared to the larger brown rat, also known as the Norway rat. The brown rat, growing up to 10 inches, showed fewer mutations and remained more susceptible to pesticides.
"Genetic mutation is not that special in these creatures," stated Jin-Jia Yu, a postdoctoral researcher at Rutgers and lead author of the study. "But we found that the house mouse shows a lot of genetic mutations related to rodenticide resistance."
Researchers believe the house mouse's tendency for curiosity and increased consumption of novel foods, including rodent bait, leads to greater exposure to poisons. This repeated exposure provides more opportunities for the development of resistance-conferring mutations. The study, initiated in 2021 after pest control companies reported decreased effectiveness of anticoagulant rodenticides, suggests these changes could undermine current pest management strategies.
Rodent infestations have been a long-standing public health threat in urban areas, serving as vectors for diseases such as hantavirus, salmonella, and plague. Hantaviruses, in particular, can cause severe respiratory illness spread through rodent droppings, urine, or saliva. Recent concerns have resurfaced regarding hantavirus, with health experts warning that a resilient strain could pose a future pandemic risk. A 2026 WHO confirmation of hantavirus cases on a ship sailing from Argentina to Cape Verde, resulting in at least three deaths, underscored the potential severity of such outbreaks.
Leptospirosis, a potentially deadly bacterial infection, has also been traced to rodent contact. In New York City, 24 cases were linked to rodents and their urine. While often starting with flu-like symptoms, leptospirosis can progress to severe complications, including kidney or liver problems and, if untreated, death.
The study's findings, published in Pest Management Science, highlight the global impact of these rodent species, noting the substantial economic losses they cause through property damage and the serious public health risks they present via zoonotic disease transmission.