WILLEMSTAD, Curacao — Authorities in Curacao on Saturday boarded a ship that arrived under quarantine to start vaccinating people to prevent a measles outbreak.

"We're not that afraid about the disease itself," said Curacao epidemiologist Dr. Izzy Gerstenbluth. "It's about doing what we can do to try to contain the spread of disease, that's all."

Health officials said only those who already have been vaccinated or have previously had measles will be free to leave the 440-foot ship Freewinds, which belongs to the Church of Scientology.

Gerstenbluth told The Associated Press that a small team is assessing more than 300 people aboard the ship, and that the process might take more than a day.

"We will go on board and do our job," he said, adding that authorities have an international obligation to avoid spreading the disease. "If we allow that to happen, measles spreads in places where the risk of severe complications is much bigger, especially when we're talking about poor countries where people have a lower level of resistance."

There is only one confirmed case of measles on board, said Gerstenbluth. He also added that vaccination levels in Curacao are "probably pretty high."

Authorities said people aboard the ship might have been exposed after a female crew member was diagnosed with measles after coming back from Europe.

Gerstenbluth said she arrived on the Dutch Caribbean island of Curacao on April 17 and visited a doctor April 22 for cold symptoms. A blood sample was taken and sent to nearby Aruba, where officials confirmed it was measles on April 29, a day after the ship had departed for St. Lucia. Curacao health officials then alerted authorities in St. Lucia.

The Freewinds cruise ship was under quarantine in St. Lucia earlier this week before it returned to its home port of Curacao early Saturday. Gerstenbluth said it would be easy to spread the disease given that it's a small ship.

"This is what happens when we don't vaccinate," he said.

According to Gerstenbluth, the woman happened to have been isolated on board "during the period in which she is contagious."

"What we don't know is how well they adhere to isolation procedures and if people were in contact with the patient before she was isolated," added the epidemiologist.

Measles symptoms include runny nose, fever and a red-spotted rash. Most people recover, but measles can lead to pneumonia, brain swelling and even death in some cases.

The disease has sickened more than 700 people in 22 U.S. states this year, with federal officials saying the resurgence is driven by misinformation about vaccines.

Church officials have not returned calls for comment. According to the church's website, the ship is the home of "a religious retreat ministering the most advanced level of spiritual counseling." It says religious conventions and seminars also are held aboard.