The Caribbean island’s health authorities barred any passengers or crew from leaving the boat while in port after learning of the measles case from “two reputable sources”.
Almost 300 passengers and crew are believed to be on board the vessel, with one person diagnosed with the highly infections viral illness.
The Scientology website describes Freewinds as “a 440-foot ship based in the Caribbean”. It characterises the vessel as a “religious retreat ministering the most advanced level of spiritual counselling in the Scientology religion” with its home port in the Dutch Caribbean island of Curacao.
The international vessel-monitoring website MarineTraffic.com also showed that a Panamanian-flagged passenger ship identified as SMV Freewinds docked in port near the Saint Lucia capital of Castries.
Scientology founder L Ron Hubbard spent much of his time at sea on a fleet of ships during the late 1960s and early 1970s after creating his “Sea Org”.
Dr Merlene Frederick-James said in a video statement posted to YouTube on Tuesday that the Saint Lucian ministry of health ordered the restriction after conferring with the Pan American Health Organisation and others about the risk of exposure to islanders. Officials told NBC News the ship has been under the quarantine since Monday.
In light of current measles outbreaks in the US and the highly infectious nature of the disease “we thought it prudent that we quarantine the ship”, Ms Frederick-James said.
The quarantine comes as the number of measles cases in the US has reached a 25-year peak with more than 700 people diagnosed as of this week, part of an international resurgence in the disease.
Public health officials blame declining vaccination rates in some communities driven by misinformation about inoculation that has left those populations vulnerable to rapid spread of infection among those with no immunity to the virus.
Health authorities in Los Angeles last month ordered quarantines on two university campuses after each one had reported at least one confirmed case.
The vast majority of US cases have occurred in children who have not received the three-way vaccines against measles, mumps and rubella (MMR), which confers immunity to the disease, officials said.
Measles is spread through casual contact with the virus, which can remain infectious in the air of an enclosed space for up to two hours after it is breathed out by someone carrying the disease.
The rate of transmission from an infected person to another person nearby who lacks immunity is about 90 per cent, and an infected person can be contagious for four days before showing signs of the disease.
Additional reporting by Reuters