MADRID (AP) — Health authorities across four continents Thursday were tracking down and monitoring passengers who disembarked a hantavirus-stricken cruise ship before its deadly outbreak was detected, and trying to trace others who may have come into contact with them since then.

In Argentina, a team of investigators tasked with determining the origins of the outbreak has yet to leave for the southern town they suspect is where a Dutch couple contracted the virus while on a bird-watching trip, officials from the country's Health Ministry told The Associated Press on Thursday.

On April 24, nearly two weeks after the first passenger had died on board, more than two dozen people from at least 12 different countries left the ship without contact tracing, the ship's operator and Dutch officials said Thursday.

Three passengers have died in the outbreak — a Dutch couple and a German national — and several others are sick. Symptoms usually show between one and eight weeks after exposure.

None of the remaining passengers or crew on the ship are currently symptomatic, the Netherlands-based Oceanwide Expeditions cruise ship company said Thursday.

The World Health Organization says the risk to the wider public is low. Hantavirus is usually spread by the inhalation of contaminated rodent droppings and isn't easily transmitted between people.

"We believe this will be a limited outbreak if the public health measures are implemented and solidarity is shown across all countries," said Dr. Abdirahman Mahamud, the WHO's alert and response director on Thursday.

1st hantavirus case on board was confirmed May 2

Three people, including the ship's doctor, were evacuated Wednesday while the ship was near the West African island country of Cape Verde and taken to specialized hospitals in Europe for treatment.

The body of the Dutch man who was the first to die on board on April 11 was taken off the ship on the remote South Atlantic island of St. Helena on April 24, when his wife also disembarked. She then flew to South Africa a day later and died there.

The ship's operator said Thursday that a total of 30 passengers — including the deceased Dutch man and his wife — left the vessel at St. Helena. The Dutch Foreign Ministry has put the figure at about 40. The company had not previously said publicly that dozens more people left the ship on April 24.

It wasn't until May 2 that health authorities first confirmed hantavirus in a passenger on the ship, the WHO says. That was in a British man evacuated from the ship to South Africa three days after the St. Helena stop. He was tested in South Africa and is in intensive care there.

Passengers who disembarked April 24 are being monitored

It emerged Wednesday that a man tested positive for hantavirus in Switzerland after he disembarked at St. Helena, though his precise movements in between aren't clear.

On Thursday, Singaporean health authorities said they were monitoring two men who got off the ship at St. Helena, flew to South Africa and then home. The two men, who arrived in Singapore at different times, were being isolated and tested, officials said.

Authorities in St. Helena, the volcanic British territory in the South Atlantic where passengers disembarked, said they were monitoring a small number of people who were considered "higher risk contacts." Those higher risk contacts were being told to isolate for 45 days, the St. Helena government said.

South Africa is tracing contacts from an April 25 flight

The Dutch health ministry said Thursday that a flight attendant on a plane briefly boarded by an infected cruise passenger in South Africa was showing symptoms of hantavirus and would be tested in an isolation ward at a hospital in Amsterdam. The cruise passenger, also a Dutch woman, was too ill to fly and was taken off the plane in Johannesburg, where she died.

If the woman tests positive, she could be the first known person not on the MV Hondius to become infected in the outbreak.

The vessel is now sailing to Spain's Canary Islands, where it is expected to arrive on Saturday or Sunday, with more than 140 passengers and crew members still on board.

WHO Director-General Tedros Adhanom Ghebreyesus said Thursday that he had been in regular touch with the ship's captain, and that morale improved once it began moving again.

Authorities in South Africa are also trying to trace contacts of any passengers who previously got off the ship. They have focused mainly on an April 25 flight from St. Helena to Johannesburg, the day after passengers disembarked there.

A French citizen with "benign symptoms" is in isolation and undergoing medical tests, after being identified as a contact case linked to the ship passenger who flew April 25 from St. Helena to Johannesburg and was confirmed to have hantavirus, the French Health Ministry said in a statement Thursday.

The Dutch woman from the cruise ship who later died in South Africa briefly boarded that flight, officials have said. It's not known how many other cruise passengers also were among the 88 people on it, but flights from St. Helena go to South Africa and are rare, normally once a week.

The body of the third fatality, a German woman, is also still on board the ship after she died on May 2.

Unlike other hantaviruses, Andes virus may spread between people

Tests have confirmed that at least five people who were on the ship were infected with a hantavirus found in South America, called the Andes virus. The only hantavirus thought to spread human-to-human, it can cause a severe and often fatal lung disease called hantavirus pulmonary syndrome.

The ship departed from Argentina and investigations into the outbreak's source are focusing there.

The Dutch couple that presented the first two cases had traveled through Argentina, Chile and Uruguay on a bird-watching trip before boarding the ship, the WHO said. They visited sites where the species of rat known to carry Andes virus was present.

Argentina's Health Ministry has zeroed in on the town of Ushuaia in their investigation, but they've yet to dispatch the team, according to a written statement given to AP. Scientists from the state-funded Malbrán Institute planned to travel to Ushuaia "in the coming days," the statement said.

Once in Ushuaia, a 3.5-hour flight from Argentina's capital, Buenos Aires, the experts will analyze rodents at the trash heap there to see if they carry the Andes virus, officials said.

The WHO is working with health authorities in Argentina to understand the couple's movements and has arranged to ship 2,500 diagnostic kits from Argentina to laboratories in five countries.

Argentina's health ministry said there were 28 deaths from hantavirus last year, up from an average mortality rate of 15 in the five years before that. Nearly a third of cases last year were fatal, it said.

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Quell reported from The Hague, Netherlands. Imray reported from Cape Town, South Africa. AP writers Jill Lawless in London and Geir Moulson in Berlin contributed.