Milder winters allow rats to have more litters, and their population explosion could help spread diseases such as E. coli and bubonic plague. Share on Pinterest Is America on the verge of a “ratpocalypse?” Experts and officials are documenting growing numbers of rats across the United States, a trend that shows no signs of slowing down. However, rats are notoriously difficult to study. The exact number of rat populations is unclear. In New York, for example, estimates range from 250,000 on the low end up to tens of millions. The only thing certain is the numbers are growing. In July, New York Mayor, Bill de Blasio, pledged $32 million to combat the rodents. The city wants “more rat corpses,” he announced. New York may be the most prominent city in the United States to tackle its highly visible rat problem, but it certainly isn’t the only one. Other major metropolitan areas, including Chicago, Boston, Philadelphia, Houston, and Washington have all reported increased sightings.

Milder winters mean more rats Bobby Corrigan, who holds a doctorate in rodentology, and is one of the nation’s leading experts on rats, told Healthline that if you spoke to health departments in 25 different cities, they’d all tell you “we have more rats now than ever before.” “Even though that’s not empirical, that’s a pretty darn good indication,” he said. Corrigan attributes growing rat populations in the United States and around the world to milder winters and growing human populations. Rats tend to reproduce less during the winter as cold weather makes it harder for the rodents to survive. But, as winters have become milder due in part to climate change over the past decade, rats have been able to produce extra litters.

More rats mean more disease The warmer weather also cascades down onto the various other parasites and bugs that depend on rats for survival. Disease-carrying ticks, mites, lice, and fleas are all more likely to survive and reproduce during mild winters. A similar problem manifested earlier this year when reports of increased tick-borne illnesses were largely attributed to booming populations of mice — the critters that spread ticks throughout forested areas. Simply put, says Corrigan, “Winter doesn’t kill as much anymore because we don’t have hard winters.” The risks of booming rat populations are manifold. The various ectoparasites that feed on rats are capable of spreading many different diseases, including rat bite fever and bubonic plague. While the plague is uncommon in the United States today, it still appears periodically, including this year in New Mexico. However, rats don’t even need to carry ectoparasites to spread disease. In fact, they are more than capable of spreading zoonotic diseases through contact with their urine and feces. A study from Columbia University in 2014 found that rats in New York carried everything from E. coli and salmonella to Seoul hantavirus and C. difficile. “They don’t carry rabies. That’s the good news,” says Corrigan.

Solutions are difficult The federal government isn’t actually involved in controlling rat populations as it is with many other public health problems. Between 1969 and 1982, the Centers for Disease Control and Prevention (CDC) doled out grants to different cities under its Urban Rat Control program, but that ended under former President Ronald Reagan. A CDC spokesperson confirmed to Healthline that it no longer has any involvement with rat control. Since then, cities, businesses, and citizens have had to fend for themselves. “You’re only as good as your worst neighbor down the street or outside the door who doesn’t do their trash right,” said Corrigan.