(CNN)Years after an outbreak was stamped out, rabies has returned to the raccoons of New York City's most densely populated borough.
Rabid raccoons are back in Manhattan. Vaccinate your pets, health officials say
Four raccoons with rabies have been found since the start of the year in the upper portion of Manhattan, the first seen on the island since 2011, the city health department said Friday.
Officials are using the discoveries to remind city residents to vaccinate their pets against the deadly disease.
"The city has done a great job keeping our wildlife free from rabies, but sometimes Mother Nature has other ideas," state Sen. Robert Jackson said in a news release.
"I urge my constituents with pets to make sure their animals are up to date on their vaccines. Stay alert when enjoying our beautiful parks, and if you see a wild animal acting strangely, leave the area and call" 311, the city's hotline for non-emergency services, he said.
Any animal that seems sick, disoriented or unusually quiet or aggressive should be reported, city officials said.
Infected animals can spread rabies to people and unvaccinated animals through a bite. No pets or people are believed to have been bitten by these raccoons, the health department said.
Rabies has been rare on Manhattan Island since an outbreak from 2009 to 2011, when 138 rabid raccoons were reported in and around Central Park. That outbreak was quelled after health department officials caught nearly 500 raccoons around the park, vaccinated them and released them.
This year's four rabies cases were found in and around upper Manhattan's Inwood Hill Park. The health department is "reminding New Yorkers to stay away from raccoons and other wild animals that can carry rabies," the department's news release reads.
From 2012 to 2018, only five rabies cases -- all involving bats -- were reported on the island.
Rabies has recently been more common in nearby areas including the Bronx, where nine animal rabies cases were reported last year.
Nationally, 5,508 cases of rabies in animals and three human rabies cases were reported to the Centers for Disease Control and Prevention in 2015, the most recent year for which national data was available.