Three people have died on a cruise ship in the Atlantic, the WHO said, with one case laboratory confirmed as hantavirus—an illness usually transmitted to humans from rodents.
The outbreak occurred on the MV Hondius, which was 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," WHO said.
The patient treated in Johannesburg tested positive for a hantavirus, a family of viruses that can cause haemorrhagic fever and severe respiratory illness.
Cases under investigation
While infections are typically linked to environmental exposure to infected rodents' urine or faeces, the WHO noted: "While rare, hantavirus may spread between people and can lead to severe respiratory illness."
The first victim, a 70-year-old passenger, died on board.
His 69-year-old wife was evacuated to South Africa, where she also died.
A third fatality remains on the ship.
Discussions are underway to decide whether two other sick passengers should be placed in isolation in Cape Verde before the ship continues to Spain's Canary Islands.
The MV Hondius, operated by Dutch-based Oceanwide Expeditions, can accommodate around 170 passengers and 70 crew members.
