The World Health Organization said Thursday that more hantavirus cases could emerge after the disease killed three passengers from a cruise ship, but it expected the outbreak to be limited if precautions were taken.

Another sick passenger from the MV Hondius landed in Europe earlier in the day, as the vessel headed to the Spanish Canary Islands and health officials scrambled to trace the outbreak of the potentially deadly human?to?human strain.

The fate of the Hondius sparked international alarm after three people travelling on it died, though health officials have played down fears of a wider global outbreak from the rat?borne virus, which is less contagious than Covid 19.

U.S. President Donald Trump said Thursday he had been briefed on the situation. "It's very much, we hope, under control," Trump told reporters.

"It was the ship -- and I think we're going to make a full report about it tomorrow. We have a lot of great people studying it... It should be fine, we hope."

A Dutch couple who had travelled around South America before boarding the ship in Ushuaia, Argentina on April 1 were the first fatalities.

Argentine health authorities said Thursday they had not yet been able to establish where the outbreak began.

"With the information provided so far by the countries involved and participating national agencies, it is not possible to confirm the origin of the infection," the health ministry said after a meeting with authorities from all 24 Argentine provinces.

Rare disease

WHO chief Tedros Adhanom Ghebreyesus told journalists in Geneva that five confirmed and three suspected cases had been reported overall, including the three deaths.

"Given the incubation period of the Andes virus, which can be up to six weeks, it's possible that more cases may be reported," he said, referring to the rare strain detected aboard the Hondius, which can be transmitted between humans.

The Leiden University Medical Centre in the Netherlands later announced another patient had tested positive.

But the WHO's emergency alert and response director Abdi Rahman Mahamud said he believed it would be "a limited outbreak" if "public health measures are implemented and solidarity shown across all countries."

People thought or known to have contracted the virus are being treated or isolating in Britain, Germany, the Netherlands, Switzerland and South Africa.

Hantavirus is a rare respiratory disease that is usually spread from infected rodents and can cause respiratory and cardiac distress as well as haemorrhagic fevers. There are no vaccines and no known cure.

A passenger is thought to have contracted the virus before boarding the ship in Argentina and infected others on board as it sailed across the Atlantic.

Officials in Argentina said they planned to test rodents in the coastal city of Ushuaia, from where the ship had set sail on April 1.

Three evacuees were whisked away from the ship on Wednesday when it anchored off Cape Verde and a fourth landed in Amsterdam on Thursday, according to the vessel's operator, Netherlands-based Oceanwide Expeditions.

The company said there were no symptomatic individuals on board as the ship sails toward the Spanish island of Tenerife, where it is scheduled to arrive on Sunday.

YouTuber Kasem Ibn Hattuta, a passenger aboard the Hondius, posted a video recounting how he learned of the first death around 12 days after the start of the trip.

"Most people on board are reacting very calmly to the situation, unlike what is being reported in the media," Hattuta said.

"Today was supposed to be the last day of our 35-day voyage across the Atlantic Ocean. But it is clear that our journey will not end here," he added, referring to Cape Verde's refusal to allow the Hondius to dock.

First case

A Dutch man who had boarded in Ushuaia along with his wife died aboard the ship on April 11.

The man's body was taken off the ship on April 24 in Saint Helena, an island in the south Atlantic where 29 other passengers disembarked, the ship's operator said.

It said it was working to trace all passengers and crew who got on or off the ship since March 20.

Tedros said the WHO had informed 12 countries that their nationals disembarked from the cruise ship on Saint Helena.

The Saint Helena government said "more than 95 percent" of the population had no close contact with the ship's passengers or crew, or boarded the vessel, and are currently "at an extremely low risk of infection".

The deceased man's wife, who left the ship to accompany his body to South Africa, died in that country 15 days later after also falling ill, with hantavirus confirmed as the cause on May 4.

The couple had visited Chile and Uruguay as well as Argentina, officials in Buenos Aires said.

Chile's health ministry said the couple were not infected in that country as they travelled there at "a period that does not correspond to the incubation time".

According to the WHO, the incubation period for hantavirus can be up to six weeks.

The Dutch woman flew on a commercial plane from Saint Helena to Johannesburg while she was showing symptoms.

Officials were trying to trace people on that flight, which South African-based carrier Airlink said was carrying 82 passengers and six crew.

A German passenger died on May 2. Her body remains on the ship.