Milder winters allow rats to have more litters, and their population explosion could help spread diseases such as E. coli and bubonic plague.

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.

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.

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.

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.

This leads to the second major part of the rat boom: humans.

Rats have been called the “mirror species” of humans. When we thrive, they thrive. They share and inhabit the same cities that we do.

“More people, more trash, more trash, more pests,” said Corrigan.

For better or worse then, the solution to the rat problem begins with the human problem of waste management.

“That’s a mammal that needs the same thing you and I need. It needs food every single day. It needs water every day,” explained Corrigan.

“If you have 16 rats, just one family of rats, they need a pound of food every night. That’s seven pounds of food every week going into those rats’ bellies,” he noted.

The implication is clear: Rats are getting all the food they need from humans.

And while calls to pest control services are up across the country, and cities are trying new methods for killing rats — like using dry ice to suffocate them in their nests — in New York, Corrigan’s approach is far more benign.

The only solution, according to Corrigan, is an approach that includes individual and government cooperation between everyone from city task forces, to grocery store and restaurant owners, to homeowners.

If you want to keep rats out of your home and help control populations, it comes down to two things, he said. Ensure that all doors, including garage doors, leading into and out of your home are tightly closed.

“You should not be able to roll a number two pencil under a door,” Corrigan said.

The second is securing garbage appropriately.

“Everybody thinks anybody can take out the garbage, so sometimes they’ll give it to the children to take out the garbage,” says Corrigan. “Taking out the garbage and storing the garbage correctly is something that needs attention.”

“Instead of hiring an exterminator or putting out poison bait, why don’t you just simply get a better garbage can?” he said.