An outbreak of hantavirus on board a cruise ship is not the start of a pandemic, the UN health agency has said.
Maria van Kerkhove, an infectious disease epidemiologist at the World Health Organization (WHO), told a news briefing that it was not the same situation as six years ago with Covid-19, because hantavirus spreads through "close, intimate contact".
Health authorities are racing to trace dozens of people who have recently disembarked from the Dutch vessel MV Hondius.
On Thursday, the WHO said that overall, five of eight suspected cases of hantavirus had been confirmed. Three people have died, including a 69-year-old Dutch woman, who had the virus.
Her Dutch husband and a German woman also died, and their cases are being investigated.
Hantavirus typically spreads from rodents - but rare instances of human transmission have been documented with the Andes strain, which is behind this outbreak. It is the first known transmission of the virus on a boat, the WHO said on Thursday.
The luxury cruise, operated by Oceanwide Expeditions, began its journey on 1 April in Ushuaia, Argentina, and is expected to arrive in Spain's Canary Islands on 10 May.
About 150 passengers and crew from 28 countries are reported to have initially been aboard the vessel, but dozens disembarked on the island of St Helena on 24 April.
At Thursday's news briefing, van Kerkhove said "this is not Covid, this is not influenza, it spreads very, very differently".
She said authorities had asked "everyone to wear a mask" on board the MV Hondius.
Those in contact with or caring for suspected cases, she added, should "wear a higher level of personal protective equipment".
At the same briefing, WHO Director General Tedros Ghebreyesus said his organisation "assesses the public health risk as low".
He said the first two people with the confirmed virus had "travelled through Argentina, Chile and Uruguay on a bird-watching trip which included visits to sites where the species of rat known to carry the virus was present".
Dr Tedros said the WHO was aware of reports of other people with symptoms who may have had contact with passengers, adding that officials were in touch with the relevant authorities.
Given the incubation period of this disease - which can be up to six weeks - it was possible more cases may be reported, he said.
Also on Thursday, Oceanwide Expedition said 29 passengers, of at least 12 different nationalities, had left the MV Hondius in St Helena, the British Overseas Territory. It said that the body of one deceased person - who is now known to be a Dutch man - was also taken off the vessel.
Seven of those who left the cruise liner were British nationals.
"Two of these individuals are now self-isolating in the UK while the others have not yet returned," an update from the UK Health Security Agency (UKHSA) said. Four remained in St Helena - and "tracing efforts are ongoing for the seventh individual, who we know has not yet returned to the UK", the statement said.
On Thursday, Spain said discussions with the UK were "very advanced" for London to send a repatriation flight for British nationals to Tenerife after the vessel's arrival to the Canary Islands.
Virginia Barcones, head of Spain's civil protection and emergencies, said there were 19 British passengers and four crew members currently on board the ship.
She said there were also four Americans on the MV Hondius, adding that "the United States has shown its willingness to send a plane that will collect its citizens directly".
Oceanwide Expeditions said the first confirmed case of hantavirus was not reported until 4 May and that all guests who disembarked the ship had been contacted.
The operator said it remained in "close and continual discussion with relevant authorities regarding our exact point of arrival, quarantine and screening procedures for all guests".
The Dutch government said the ship stopped in St Helena on its way to Cape Verde, an archipelago nation off the West African coast.
It said the Dutch woman who left the cruise on 24 April travelled to South Africa, where she died two days later.
Her husband died on board the ship on 11 April, but is not a confirmed case of hantavirus.
The update said the woman had boarded a KLM flight heading from Johannesburg to the Netherlands, but became ill before its departure.
Authorities in the Netherlands are sending letters to passengers who were on the flight, asking them to remain "available for monitoring".
The third fatality - a German woman - died on board the MV Hondius on 2 May, and is not a confirmed case either. Her body remains on the ship.
Three other people - British, Dutch and German nationals - were evacuated from the vessel on Wednesday.
Singapore's Communicable Diseases Agency said it was isolating and testing two men - a 67-year-old Singaporean and a 65-year-old permanent resident - who disembarked the ship in St Helena.
It added that they had taken the same flight from St Helena to Johannesburg in South Africa as the 69-year-old woman who died. Their hantavirus test results are still pending.
Two US states - Georgia and Arizona - confirmed to the BBC that they were monitoring three passengers who returned to the US after disembarking. None were displaying symptoms. The US Department of State said it was in "direct contact" with affected passengers.
Argentina's health ministry has said officials will test rodents in Ushuaia.
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Correction 8 May: An earlier version of this story reported that transmission between people had been documented for the first time in this outbreak, according to the WHO. In fact, the WHO said on Thursday that this is the first time human transmission has been documented on a boat. Human transmission is rare but has previously been seen with the strain of the virus behind this outbreak. The article has been amended to reflect this.
