South African health authorities have identified the Andes strain of hantavirus, which can be transmitted from person to person, in two passengers aboard a luxury cruise ship at the centre of an outbreak of the rare infection, officials said Wednesday.

The Spanish Health Ministry on Tuesday said it had been asked by the World Health Organisation and the European Union to take the MV Hondius and had given its agreement "in accordance with international law and humanitarian principles."

Cape Verde has not allowed the vessel to allow passengers ashore because of the outbreak.

The MV Hondius, a Dutch ship on a week-long polar cruise from Argentina, left Ushuaia on April 1 and visited Antarctica and several isolated islands in the South Atlantic Ocean, the World Health Organization said Tuesday.

Three passengers have died in the outbreak of the rodent-borne virus on the cruise ship, which is now sitting off the coast of Cape Verde in West Africa, and at least four others have fallen sick. A Dutch couple and a German national who had been on the ship are among the dead, while a British national is in intensive care in South Africa. Three patients remain on board and are expected to be evacuated.

The virus is spread by rodents and, more rarely, people. It is typically contained because it spreads only through close contact, such as sharing a bed or food, experts say.

Confirmation that the cruise ship Hantavirus outbreak can spread from human-to-human does not change the World Health Organization's (WHO) risk assessment, which remains at low risk, the U.N. body's South Africa representative said.

"No, it doesn't change the risk assessment because ... it's primarily (spread) when one gets into contact with an infected rodent and even ... human to human is (only spread) within very, very close contacts," Shenaaz El-Halabi told Reuters in a video call.

The South African Department of Health said the information came from tests performed on the passengers after they were removed from the ship and flown to South Africa.

One of the passengers, a British man, is in intensive care in a South African hospital. Tests were performed on the other passenger posthumously after she died in South Africa.

A German national who was onboard a luxury cruise ship hit by a deadly hantavirus will be brought to a hospital in the German city of Duesseldorf for testing, Bild reported, adding that the woman presented no symptoms.

According to the WHO, the Andes virus, a specific species of hantavirus, is found in South America, primarily in Argentina and Chile.

The Swiss government said a man who returned to Switzerland after being a passenger on the MV Hondius was infected with the hantavirus and was being treated in Zurich, adding there was no danger to the broader population.

Authorities are coordinating the evacuation of three patients who remain on board, with the Netherlands leading efforts to transfer them for treatment. The ship is expected to dock at the Canary island of Tenerife, Spanish state broadcaster TVE reported on Wednesday, citing sources from the country's health ministry.

Human-to-human transmissions

People are usually infected by hantavirus through contact with infected rodents or their urine, droppings or saliva. Human-to-human transmission is rare.

But limited spread among close contacts has been observed in some previous outbreaks with the Andes strain, which has spread in South America, including Argentina.

Hantaviruses, common in different parts of the world, cause different symptoms or diseases — and some cause none at all.

Symptoms typically begin one to eight weeks after exposure and may include fever, muscle aches and gastrointestinal issues, according to the WHO.

In Europe and Asia, hantaviruses have been known to cause haemorrhagic fever with renal syndrome, which mainly affects the kidneys and blood vessels.

In the Americas, infection can cause hantavirus cardiopulmonary syndrome, which progresses quickly and leads to fluid buildup in the lungs along with heart complications.

Fatality rates from hantavirus cardiopulmonary syndrome are up to 50%, the WHO says, compared to 1-15% from the infections common in Asia and Europe.

There is no specific treatment for infection from hantavirus, so current therapy focuses on supportive care, including rest and fluids. Patients may need breathing support such as a ventilator.

Prevention focuses on limiting contact with rodents through measures like keeping areas and surfaces clean.

During outbreaks, contact tracing can give others potentially exposed to the virus earlier access to hospital care, improving outcomes and preventing further spread.

WHO's Americas branch had warned in December that hantavirus infections were rising in the region, particularly in Bolivia and Paraguay. Brazil and Argentina — which has the most cases — have also seen rising lethality.

Argentina reported 21 deaths last year, a 32% fatality rate among 66 who contracted hantavirus pulmonary syndrome, compared with a 15% average over the past four years.

A presentation seen by Reuters said tests done by South Africa's National Institute for Communicable Diseases revealed that the Andes strain was the cause of infection in the Dutch woman who died in Johannesburg, as well as in the British man who is still in hospital there.

"This is the only strain that is known to cause human-to-human transmission, but such transmission is very rare and, as said earlier, it only happens due to very close contact," the presentation said.

South Africa's health ministry also said that contact tracing was underway, with 62 contacts identified, including flight crew and healthcare workers. The contacts will be monitored until an incubation period has passed, and none have been diagnosed with the hantavirus so far.

The Spanish archipelago's leader, Fernando Clavijo, said he was opposed to the move and requested an urgent meeting with Prime Minister Pedro Sanchez. The decision ultimately belongs to the central government, which supersedes regional authorities.

Meanwhile, the Dutch foreign ministry said all efforts were aimed at evacuating the remaining patients as soon as possible, adding that exact details of timing and logistics would be shared once finalised.