Oh Rats! They’re Everywhere and Spread Diseases Like Leptospirosis


Q: We don’t live all that far from Central Park in New York, and it appears there are more rats than ever – even during the day. I know about leptospirosis, and that dogs can walk in a puddle and lick paws, so I wipe their paws with soapy water when we go back into the house if I think my dog has walked through a puddle. And I don’t let my dog drink from puddles outside.

This coyote in Central Park is about to catch a rat

Meanwhile, some people want to kill the coyotes in the park, who are likely helping to keep the rats in check. I know the rat population is worse because so many restaurants have limited hours, if they’re open at all – so they don’t have as much in their garbage which rats depend on. Is there anything else that can be done, short of rat poison which is deadly not only to dogs but I worry that the poison can get into our water table as well. Rat poison in the environment can’t be good. B. C., Manhattan, NY.

A: Lots to address here: It’s not your imagination, there may be more rats than ever. Or perhaps, the rats are merely more visible. That’s hard to say.

In places where humans share rivers with animals leptospirosis is very common.

Leptospirosis is a disease caused by infection with Leptospira bacteria, which can be shed by not only city rats but any type of rodent (such as mice and squirrels), racoons, skunks, coyotes, as well as assorted animals found on farms and many more including unvaccinated dogs. Not only does the vaccine protect dogs against lepto it also prevents dogs from sharing the illness with others. These Leptospira bacteria can be found worldwide in soil and especially thrive in fresh water. That water can range from a river to even retention ponds found in condominium developments or puddles. Any body of water – large or small – that any infected animal urinates in.

According to one study, as many as eight percent of dogs are shedding leptospires causing others to get sick – potentially including humans as the dogs shedding the infection may themselves be asymptomatic. If an infected dog (most often a puppy) has an accident indoors, and a human who cleans up doesn’t wash up – that person may be infected with the disease which may cause kidney failure, and even be fatal in dogs or people. Rats (and other rodents) appear to be impervious to the effects of the infection.

Vaccination is Most Effective Means of Prevention

Dog lapping from a puddle appears harmless – but it always isn’t.

Indeed, simply wiping dog paws with soapy water likely could prevent dogs from getting lepto from licking paws, though I know of no data regarding effectiveness of this method of prevention. No matter, I’m unsure how practical it is.  Also, preventing dogs from drinking water from puddles or ponds or rivers outside is advised. However, vaccination is your best bet, by far, to prevent leptospirosis in dogs.

Now, as for those rats. I predicted way early on in the pandemic what the CDC has now confirmed regarding rat lifestyle changes as a result of their primary food source being impacted by limited restaurant hours and restaurant closings. For as long as there have been restaurants, rats have found a way to take advantage of the trash.

What’s more, this is the time of year when young rats born just a few months ago are seeking food competing with older rats. In climates like New York, they gorge before winter. So, now is indeed a time when more rats are out and about – even during the day. And with their usual food sources more limited, some rats are bolder about getting to whatever they can, from backyard bird feeders to residential trash.

I agree, while coyotes can spread leptospirosis, allowing them to help control the rat population is likely of greater benefit.

Rat Abatement Methods

I also agree with you regarding rat poison. Not only can dogs – and a variety of species – get into the poison, it is not an environmentally friendly solution. What’s more, rat poison isn’t a perfect.

Get this: Rats can to do autopsies

When a rat returns to a colony and dies, believe it or not, other rats smell cause of death, and learn to avoid ingesting that poison.

Some cities have tried to drop dry ice into rat holes, The method of stuffing dry ice — frozen carbon dioxide — into burrows to suffocate rats as it sublimates from a solid to a gas proved more efficient at killing rats and cheaper than using conventional rat poisons in cities such as Boston, Chicago and New York. However, the U.S. Environmental Protection Agency put an end to the practice. And today, all the available dry ice is needed to maintain the upcoming COVID-19 vaccine.

Trash cans like this are an open invite to rats if there’s food inside, and big cities are filled with these. New York City has tried to control what people toss into the cans, but that’s nearly impossible

So what’s the best solution to control rats? Indeed, limiting trash – while making rats more desperate – is a solution that is helpful over time.

And another solution are cats. Tree House Humane Society in Chicago was arguably the first in the country to develop a program called Cats at Work. Two or more community cats (feral cats) that have been spay/neutered are placed into residential or commercial settings in order to provide environmentally friendly rodent control. Property and business owners provide food, water, shelter, and wellness to the cats who work for them. This is arguably the most natural method of rat control, not to mention the most efficient.

Leptospirosis was once thought to be a problem only where there are farm animals and out in the countryside. However, with an abundance of urban wildlife – not to mention those city rats – studies have shown that lepto is even more prevalent in urban areas. And while there’s no downside to soap and water, the only proven way to prevent is vaccination.