Three passengers from the ship - a Dutch husband and wife and a German woman - have died, while others have fallen sick with the rare disease, which usually spreads among rodents.

The only hantavirus type that can transmit from person to person - the Andes virus - has been confirmed among those who have tested positive, fuelling international concern.

It has also sparked fears among people of the Canary Islands, with regional authorities having refused to allow the vessel to dock, deciding it will remain offshore while passengers are screened and evacuated.

'Strain of hantavirus is serious'

In his open letter, Tedros hailed the people of Tenerife for their solidarity and said he had thanked Spanish Prime Minister Pedro Sanchez personally for Spain agreeing to take on its "moral duty" and receive the ship.

"I know you are worried," Tedros wrote in his open letter.

"I know that when you hear the word 'outbreak' and watch a ship sail toward your shores, memories surface that none of us have fully put to rest. The pain of 2020 is still real, and I do not dismiss it for a single moment," he said.

Tedros acknowledged that the Andes strain of hantavirus "is serious".

"Three people have lost their lives, and our hearts go out to their families," he said, stressing though that "the risk to you, living your daily life in Tenerife, is low".

"This is the WHO's assessment, and we do not make it lightly."

An expert with the United Nations health agency was on board and had determined that currently "there are no symptomatic passengers", Tedros said.

He also highlighted that "medical supplies are in place" and stressed that Spanish authorities had prepared a "careful, step-by-step plan" for the evacuation.

According to that plan, he said, "passengers will be ferried ashore at the industrial port of Granadilla, far from residential areas, in sealed, guarded vehicles, through a completely cordoned-off corridor, and repatriated directly to their home countries".

"You will not encounter them. Your families will not encounter them."

Deemed 'nearest port'

The WHO chief insisted the request for Spain to receive the ship "was not made arbitrarily", pointing out that under International Health Regulations, "the nearest port with sufficient medical capacity must be identified to ensure the safety and dignity of those on board".

"Nearly 150 people from 23 countries have been at sea for weeks, some of them grieving, all of them frightened, all of them longing for home," he said.

Tedros said he was travelling to Tenerife to observe the evacuation operation personally, to "stand alongside" health workers and port staff, and to "pay my respects" to the island and its response.

"The WHO stands with you, and with every person on that ship, every step of the way," he said.

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