CAPE TOWN, South Africa (AP) — A suspected outbreak of the rare hantavirus infection on a cruise ship in the Atlantic Ocean killed three people, including an elderly married couple, and sickened at least three others, the World Health Organization and South Africa’s Department of Health said Sunday.

In a statement to The Associated Press, WHO said an investigation was underway but that at least one case of hantavirus had been confirmed. One of the patients was in intensive care in a South African hospital, the U.N. health agency said, and it was working with authorities to evacuate two others with symptoms from the ship.

The Dutch company that operates the cruise said the ship was now sitting off the coast of Cape Verde, an island nation off Africa’s west coast, and local authorities were assisting but had not allowed anyone to disembark. It said the two sick people onboard requiring urgent medical care were crew members.

Hantavirus infections are spread mainly by rodents

Hantaviruses, which are found throughout the world, are a family of viruses spread mainly by contact with the urine or feces of infected rodents like rats and mice. They gained attention after the late actor Gene Hackman’s wife, Betsy Arakawa, died from hantavirus infection in New Mexico last year.

Hackman died around a week later at their home from heart disease.

Hantaviruses cause two serious syndromes, according to the U.S. Centers for Disease Control and Prevention: hantavirus pulmonary syndrome, a severe disease that effects the lungs, and hemorrhagic fever with renal syndrome, a severe disease that affects the kidneys.

While rare, WHO said hantavirus infections can be spread between people. There is no specific treatment or cure, but early medical attention can increase the chance of survival.

“WHO is aware of and supporting a public health event involving a cruise vessel sailing in the Atlantic Ocean,” the organization said. “Detailed investigations are ongoing, including further laboratory testing, and epidemiological investigations. Medical care and support are being provided to passengers and crew. Sequencing of the virus is also ongoing.”

The weekslong cruise started in Argentina

South Africa’s Department of Health said the ship, the Dutch-flagged MV Hondius, had left Argentina around three weeks ago for a cruise that included visits to Antarctica, the Falkland Islands and other stops. It was due to ultimately head to Spain’s Canary Islands on the other side of the Atlantic.

The first victim was a 70-year-old man who died on the ship and whose body was removed in the British territory of Saint Helena in the South Atlantic, the South African health department said in a statement. The man’s wife collapsed at an airport in South Africa trying to take a flight to her home country of the Netherlands, the department said. She died at a nearby hospital.

The department identified the patient in intensive care in a hospital in Johannesburg as a British national. It said that person fell ill near Ascension Island, another remote island in the Atlantic, after the ship left Saint Helena and was transferred from there to South Africa.

Around 150 passengers were onboard

Around 150 tourists were onboard at the time of the outbreak, South Africa’s health department said. Several online tour operators said the Hondius, which is described as a specialist polar cruise ship, usually travels with around 70 crew members.

Oceanwide Expeditions, the company that runs the cruise, said the third victim’s body was still onboard the ship in Cape Verde and its priority was to ensure the two crew members who were ill received medical care.

“Local health authorities have visited the vessel to assess the condition of the two symptomatic individuals,” the company said. “They are yet to make a decision regarding the transfer of these individuals into medical care in Cape Verde.”

WHO said it was working with national authorities and the ship’s operators to conduct a “full public health risk assessment” and provide support for those still onboard.

South Africa’s National Institute for Communicable Diseases, meanwhile, was conducting contact tracing in the Johannesburg region to identify if other people were exposed to the infected passengers in South Africa.