A new study has revealed widespread genetic mutations among mice and rats in several major US cities, giving them an increased ability to resist toxins used to combat them.
This raises concerns about the difficulty of controlling these rodents, which are among the most prominent vectors of diseases to humans.
The study, conducted by researchers from Rutgers University in New Jersey, showed that the majority of rodents examined in New York, New Jersey, Pennsylvania, and Washington, D.C., carried genetic mutations associated with resistance to common rodenticides.
The study, which included nearly 300 house mice and brown rats, revealed that five out of six rodents carried at least one mutation in the Vkorc1 gene, known to reduce the effectiveness of rodenticides. It also showed that over 69% of the samples carried additional mutations previously linked to pesticide resistance.
Jin Jia Yu, a postdoctoral researcher at Rutgers University and lead author of the study, said that genetic mutations are not uncommon in these creatures, but the results showed that the house mouse carries a large number of mutations directly linked to rodenticide resistance.
According to the study, these mutations were more prevalent among small house mice than brown rats, suggesting that this species is developing pesticide resistance at a faster rate. Researchers attribute this to the house mice's tendency to frequently experiment with new food sources, including the poison bait used to control them.
The researchers explained that continuous exposure to toxins increases the chances of survival for individuals who are able to resist them, allowing these genetic traits to be passed on to subsequent generations and making traditional control methods less effective over time.
In contrast, the results showed that the brown rat, also known as the sewer rat, is still less resistant to pesticides due to its lower rate of resistance-related gene mutations, despite having behavioral abilities that help it avoid traps and suspicious food sources.
These findings are of particular importance because of the health risks associated with the spread of rodents in cities, as they are carriers of a number of diseases, including Hantavirus, Salmonella, Plague and Leptospirosis.
Hantaviruses are typically transmitted through inhaling fine particles from rodent droppings, urine, or saliva, and can also be transmitted through bites and scratches. Symptoms of infection include fever, fatigue, and muscle aches, and can progress to serious respiratory problems.
New York City also recorded 24 cases of leptospirosis linked to exposure to rodents or their urine, a disease that in severe cases can lead to serious complications including liver or kidney failure, bleeding, and death.
Official data reflects the scale of the problem in American cities; 29% of households in Philadelphia reported spotting rats inside their homes, while 15% of Manhattan residents in New York reported suffering from a rat problem, and about one-fifth of Washington, D.C. residents said they faced the same problem.
Researchers believe that the continued development of genetic resistance in rodents may pose increasing challenges to control efforts in the coming years, calling for the search for more effective methods to limit its spread and reduce the associated health risks.
