The World Health Organization said Sunday that three people have died aboard a cruise ship in the Atlantic Ocean, one a confirmed case of hantavirus, an illness usually transmitted from rodents to humans.

The outbreak occurred on the MV Hondius, travelling from Ushuaia in Argentina to Cape Verde.

"To date, one case of hantavirus infection has been laboratory confirmed, and there are five additional suspected cases," the WHO told AFP.

"Of the six affected individuals, three have died and one is currently in intensive care in South Africa."

Earlier Sunday, South Africa's health ministry told AFP there had been an outbreak of a "severe acute respiratory illness", which had killed at least two people, with a third in intensive care in Johannesburg.

The patient treated in Johannesburg tested positive for a hantavirus, a family of viruses that can cause hemorrhagic fever, South African spokesperson Foster Mohale said.

In its statement, the WHO said: "Hantavirus infections are typically linked to environmental exposure (exposure to infected rodents' urine or faeces).

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

Husband and wife

The first person to develop symptoms was a 70-year-old passenger. He died on board the ship and his body was currently on the island of Saint Helena, a British territory in the South Atlantic, Mohale the South African spokesman said.

His 69-year-old wife also fell ill on board and was evacuated to South Africa, where she died in a Johannesburg hospital, he said, adding that they were not yet able to confirm the victims' nationalities.

The third case, a 69-year-old Briton, was also evacuated to Johannesburg, where he was being treated in intensive care.

A source close to the case speaking on condition of anonymity had said a Dutch couple were among the dead. The third fatality was still on board the ship.

Discussions were under way to decide whether two other sick passengers should be placed in isolation in hospital in Cape Verde, after which the ship would continue to Spain's Canary Islands, the anonymous source said.

The WHO said it was "facilitating coordination" between national authorities and the ship's operators to organize the medical evacuation of two passengers with symptoms.

The MV Hondius is listed as a polar cruise ship on the websites of several travel agencies. It is operated by a Dutch-based tour company, Oceanwide Expeditions.

One of the cruises offers an itinerary departing from Ushuaia for Cape Verde, with stops in the islands of South Georgia and Saint Helena.

According to several online ship-tracking sites, the MV Hondius was just off the port of Praia, the capital of Cape Verde, on Sunday.

The vessel can accommodate around 170 passengers and has some 70 crew members.

Humans can catch hantaviruses from contact with infected mice or rats or their droppings, or being bitten or inhaling contaminated dust. There are multiple types of hantaviruses in different parts of the world, with different symptoms.

AFP contacted the cruise operator Oceanwide Expeditions but has not yet had a reply.