City health officials are warning visitors to Central Park to avoid contact with wild animals and to keep their dogs on a leash following the discovery of three rabid raccoons, two in the last week.

The discovery was a surprise because, in the previous six years, only one rabid animal had been found in Manhattan, with the majority of rabies cases in the city isolated to Staten Island and the Bronx. Another rabid raccoon that was found earlier this year, near the northernmost tip of Manhattan, was believed to have crossed over from the Bronx on a railroad bridge.

“There is concern that it could spread to more raccoons,” said Dr. Sally Slavinski, a public health veterinarian for the New York City Department of Health and Mental Hygiene. City employees will be enhancing their surveillance of the park to look for signs of other sick animals and are urging parkgoers who spot disoriented or aggressive animals to report them by calling the city’s 311 information line.

There hasn’t been a human infection of rabies in New York City since 1953, around the time that the city began mandating rabies vaccinations for dogs to combat the disease, according to the health department. At the time, the disease, which is transmitted through a bite from an infected mammal and is usually fatal without treatment, was a significant problem in the city. One report described a dog frothing at the mouth racing through the crowd at a public pool and biting the officer who finally captured it.

In the early 1950s, before vaccination programs curbed the cases, about 40,000 people were bitten by rabid dogs nationwide each year, with about 40 people dying annually from the disease, according to news reports from the time. In 2007, the most recent year for which figures were available, just one person contracted the disease, according to the federal Centers for Disease Control and Prevention. (Worldwide, however, rabies remains a major killer.)

In New York State, 512 animals were identified as carrying rabies, the third most in the nation after Texas and Virginia, according to the Centers for Disease Control. Most rabies cases now involve wild animals, with raccoons being the most common carrier, followed by bats, skunks and foxes. (Nationwide, domestic animals like dogs, cats and cattle account for less than seven percent of all infected animals).

The variant of raccoon-borne rabies did not arrive in New York City until 1992 but now accounts for the majority of cases in the city and the state, said Ms. Slavinski. So far this year, 20 rabies cases have been identified in the city: 14 raccoons in the Bronx, 4 raccoons in Manhattan, a raccoon in Queens and a bat in Staten Island. In the previous six years, the Bronx has had 78 cases, followed by Staten Island with 69, Queens with 7, Brooklyn with 2 and Manhattan with 1, according to the health department.