Leptospirosis Spread in New York City to Humans and Dogs Motivates Rat Birth Control


Veterinarians have warned about this – and it’s now happening. Post pandemic, as city rats numbers continue to climb around the U.S., leptospirosis is being spread to unvaccinated dogs, and New York City is now identifying the disease in people.

Species ranging from coyotes to cattle also spread lepto, Currently, rats are leading the way. Where there are city rats, there’s leptospirosis. The more rats, the greater the risk.

The New York City Department of Health and Mental Hygiene has released a health advisory after multiple cases of human leptospirosis. There were 24 cases of leptospirosis in the city in 2023, higher than in any prior year. So far, this year, there have been six New Yorkers identified with lepto. And in 2002, a New York City resident died as a result of indirect exposure to rats (touching a trash container where an infected rat had once urinated on).

There is no CDC for pets, but veterinarians in urban areas agree they are treating more leptospirosis in dogs with each passing year. This is particularly unfortunate, as vaccination will prevent lepto.

Some people or dogs can get lepto but are asymptomatic, or with mild illness so it often goes undiagnosed. Others suffering from severe leptospirosis can have acute renal and hepatic failure, and this disease can be fatal. Internationally, leptospirosis kills approximately 60,000 people according to the Centers for Disease Control.

New York City Mayor Eric Adams wants to see fewer plastic trash bags on the streets Rats easily work their way into the bags.

Currently, the rat population in New York exceeds the human population. Mayor Adams’ office is serious about diminishing rat numbers, and even hired Kathleen Corradi who’s title is Rat Czar. The city has also invested $3.5m to launch the Rat Mitigation Zone in Harlem, an initiative to lower the number of rat sightings. Officials have noted that there’s been a 20 per cent decrease in non-emergency rat calls since the launch of these efforts.

Cities, including New York are moving away from using rodenticides. Dogs and other animals can get into the poisons, potentially even young children. On the federal level, a bill currently in committee, would ban the traps nationwide.

A Eurasian Owl named Flaco had escaped from the Central Park Zoo in 2023, The owl had become a kind of local celebrity. Flaco was found dead earlier this year, apparently flying into a building. The necropsy (an animal autopsy) revealed Flaco had rodenticide in his system.  Experts believe the poison created disorientation, and may explain why the owl flew into a building.  In New York City, this news was upsetting.

Over time, poisons dissolve into the water table. What’s more, rodenticides have limited effectiveness. When a rat returns home (to the rathole) and the succumbs to the poison, comrades sniff what led to their buddy’s demise; they instantly learn to not make the same mistake.

New York is about to launch a rat birth control program. The contraceptive, called ContraPest, is contained in salty, fatty pellets that are scattered in rat-infested areas as bait. It works by targeting ovarian function in female rats and disrupting sperm cell production in males.

It’s unclear – but hopefully other species won’t be affected by the contraceptive.

As for dogs, protection from leptospirosis is as simple as vaccination and also doing what you can to prevent dogs in urban areas from drinking at any source of water other than one which you provide.

Consistent with rat control are common sense tips such an ensuring all trash is in metal trash cans with sealed lids, rats like bird seed so ensure bird feeders are rat-proof, and potential nesting places such as old tires are appropriately disposed so they don’t become rat homes.