Rare human-to-human transmission is suspected behind an outbreak of hantavirus that has killed three people on a luxury cruise ship.

The World Health Organisation said in most cases hantavirus is spread from rats to humans, but in this case it appeared to have spread between passengers while on board the MV Hondius.

It was suspected the initial case was a couple who joined the ship in Argentina. The couple was probably infected before embarking — perhaps while doing activities such as birdwatching, said the WHO.

It said the disease may have then spread from human to human during close contact on the ship.

In total there have been seven cases and three deaths — a Dutch couple and a German national — in the deadly outbreak.

A British national was evacuated from the ship and is in intensive care in South Africa, officials said.

Three more suspected cases affect people who are still on board, one of whom has a mild fever.

Four Australians are on board the cruise ship, which is marooned off Cape Verde — an island nation in the Atlantic off West Africa — and not allowed to put passengers ashore.

WHO Centre on Global Health Law director Larry Gostin said the MV Hondius outbreak was very worrying.

“It’s possible that more cases will arise,” he told Britain’s Sky News.

“There’s no antiviral or so-called cure, but you need really intense management of the disease and so you have to get someone into really intensive care quite quickly.”

The WHO said the focus was on evacuating the two sick passengers onboard to the Netherlands and then for the ship to continue to the Canary Islands.

Human-to-human transmission of hantavirus is uncommon. The ⁠WHO reiterated the risk to the wider public was low from a disease that typically spread from infected rodents and only rarely passes ​between humans.

People are usually infected by hantavirus through contact with infected rodents or their urine, their droppings or their saliva.

However, a limited spread among close contacts has been observed in some previous outbreaks with the Andes strain, which the WHO believes could be involved in this instance.

“We do believe that there may be some human to human transmission that’s happening among the really close contacts, the husband and wife, people who have shared cabins,” Maria Van Kerkhove, WHO director of epidemic and pandemic preparedness and prevention, said in Geneva on Tuesday.

“Some people on the ship were couples, they were sharing rooms ⁠so that’s quite intimate contact.”

Van Kerkhove said the agency’s working assumption was the ‌hantavirus on the ship ​was the Andes virus, which spread in South America, including Argentina, and that testing was under way.

The Hondius left Ushuaia in southern Argentina in March.

Anyone symptomatic on the ship and those caring for ​patients were wearing full ‌personal protective equipment, with extra supplies having been brought on to the boat, Van Kerkhove said.

The WHO said it had been told there were no ​rats on board.

While the organisation said the ship would head to the Canary Islands, Spain’s health ministry said it not yet decided to receive it.

The Hondius set off on its luxury cruise from the southern tip of Argentina in late ‌March. It visited the Antarctic peninsula and South Georgia and Tristan da Cunha — some of the remotest islands on the planet.

The first stricken passenger, the Dutch man, died on April 11.

His body remained on board until April 24, when it “was disembarked on St Helena, with his wife accompanying the repatriation”, cruise operator Oceanwide Expeditions said.

His wife, who had gastrointestinal symptoms when she was disembarked, later deteriorated during a flight to Johannesburg.

She died on arrival at the emergency department on April 26, the WHO said. Contact tracing is under way for passengers on that flight.

South African authorities have confirmed that the British patient, who is being treated in a Johannesburg hospital, tested positive for the hantavirus.

The ​Netherlands has confirmed the virus in the Dutch woman ⁠who died.

-with AAP