A bird-watching tour in a region that had never recorded a hantavirus case is now at the center of an urgent investigation, as Argentine officials examine whether a Dutch couple unknowingly brought the deadly virus aboard a cruise ship after a stop at a landfill.

Argentina’s leading hypothesis is that a Dutch couple may have been exposed to rodents while visiting the landfill during the tour in the city of Ushuaia, contracting the virus before boarding the cruise ship, two Argentine officials investigating the origins of the outbreak told The Associated Press on Wednesday.

Hantavirus usually spreads by inhaling contaminated rodent droppings. The World Health Organization (WHO) said human-to-human transfer is uncommon, but possible.

Authorities previously said Ushuaia and surrounding Tierra del Fuego province had never recorded a hantavirus case.

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The Dutch-flagged MV Hondius ship is at the center of an outbreak that has already killed three passengers and sickened several others. Contact tracing is underway across Europe and Africa to track possible spread among passengers who have since disembarked.

Testing in Switzerland, South Africa and Senegal has confirmed that this is the Andes strain, according to authorities. The WHO says the variant is found primarily in Argentina and Chile and can spread through close contact, though rare.

Swiss officials said a man who returned from the cruise sought treatment after developing symptoms and was immediately isolated. They said he tested positive for the Andes strain.

WHO Director-General Tedros Adhanom Ghebreyesus said Wednesday that three suspected cases were evacuated from the vessel and are being transported to the Netherlands for treatment.

"At this stage, the overall public health risk remains low," Tedros said.

The Associated Press contributed to this report.

A suspected hantavirus outbreak aboard a cruise ship in the Atlantic Ocean has left three people dead and several others ill, the World Health Organization (WHO) said in a statement posted to X.

The U.N. health agency said one case of hantavirus infection has been laboratory confirmed, while five additional suspected cases are pending. Of the six people affected, three have died and one is currently in intensive care in South Africa.

The WHO said it is coordinating with governments and the ship’s operator to arrange the medical evacuation of two symptomatic passengers, while continuing to assess the public health risk to those still on board.

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"Detailed investigations are ongoing, including further laboratory testing, and epidemiological investigations," the WHO said. "Medical care and support are being provided to passengers and crew. Sequencing of the virus is also ongoing."

The outbreak is linked to the m/v Hondius, a Dutch-flagged cruise ship sailing in the Atlantic Ocean off the coast of West Africa.

Oceanwide Expeditions, which operates the vessel, confirmed that three passengers died during the voyage and that one passenger is being treated in intensive care in Johannesburg.

Two crew members on board also require urgent medical care, the company said.

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As of late Sunday, authorities in Cape Verde had not authorized the disembarkation of passengers requiring medical treatment or broader medical screening, according to the company.

Local health officials have boarded the vessel to assess the situation but have not yet approved the transfer of symptomatic individuals to facilities on land.

"The priority of Oceanwide Expeditions is to ensure that the two symptomatic individuals on board receive adequate and expedited medical care," the company said.

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Dutch authorities are working to coordinate the repatriation of those affected from Cape Verde to the Netherlands, though the effort depends on approval from local officials, Oceanwide Expeditions said. 

Hantavirus infections are typically linked to exposure to infected rodents’ urine or feces and can lead to severe respiratory illness.

"While rare, hantavirus may spread between people, and can lead to severe respiratory illness and requires careful patient monitoring, support and response," WHO said.

There is no specific cure for the virus, though early treatment can improve survival.

WHO said it has notified global health authorities under international regulations and is continuing to support the response.

"We are currently establishing the full facts and working on appropriate medical care, screening, and next steps," Oceanwide Expeditions said.