CAPE TOWN, South Africa >> A cruise ship with nearly 150 people aboard was waiting for help off the coast of Cape Verde in the Atlantic Ocean on Monday after three passengers died and at least three other people were left seriously ill in a suspected outbreak of the rare hantavirus, according to the World Health Organization and the ship’s operator.

The MV Hondius, a Dutch ship on a weekslong polar cruise from Argentina to Antarctica and several isolated islands in the South Atlantic, had requested help from local health authorities after making its way to the island of Cape Verde, off the West Africa coast. But no one has been allowed to disembark, Netherlands-based operator Oceanwide Expeditions said.

Cape Verde’s Health Ministry said Monday that for now, it will not allow the ship to dock because of public health concerns and that it would stay in open waters close to shore.

Hantavirus is a rodent-borne illness spread by contact with rodents or their urine, saliva or droppings. WHO says that while it is rare, hantavirus may spread between people.

It was unclear how an outbreak could have started, and WHO said it was investigating while working to coordinate the evacuation of two sick crew members. Another sick person — a British man evacuated to South Africa on April 27 — tested positive for the virus, authorities said.

The body of one of the passengers who died — a German — remains on the ship, according to an Oceanwide Expeditions statement. A 70-year-old Dutch man died onboard April 11, and his 69-year-old wife died later in South Africa after leaving the ship, officials said. Her blood later tested positive for the virus, making two confirmed cases, South Africa’s health minister said.

Among the 87 remaining passengers, 17 are Americans, 19 are from the U.K. and 13 from Spain, according to Oceanwide Expeditions. Sixty-one crew members also are onboard.

Two sick crew members — one British, one Dutch — have respiratory symptoms and need urgent medical care, Oceanwide said in its statement.

Cape Verde has sent a medical team of two doctors, a nurse and a laboratory specialist to the ship over three trips, said Dr. Ann Lindstrand, a WHO official in Cape Verde.

She told The Associated Press in an interview that they were planning for medical evacuations, in which passengers would be taken from the ship via ambulance to an airport.

Oceanwide said it would consider moving to one of the Spanish islands if it can’t evacuate passengers in Cape Verde.

WHO said it was working with local authorities and Oceanwide on a “full public health risk assessment.”

“Detailed investigations are ongoing, including further laboratory testing, and epidemiological investigations,” WHO said. “Medical care and support are being provided to passengers and crew.”

Lindstrand told AP there was a possible new case on the ship, in a person showing mild fever symptoms, but health workers were still assessing.

For the rest of the Hondius’ trip, Oceanwide Expeditions didn’t specify an itinerary. The company advertises 33-night or 43-night “Atlantic Odyssey” cruises on the vessel.

It has 80 cabins and a capacity of 170 passengers, and it typically travels with about 70 crew members, including a doctor, the company said.

The Dutch man was the first victim, and he presented with fever, headache, abdominal pain and diarrhea, officials said. His body was taken off the vessel nearly two weeks later on the British territory of Saint Helena, some 1,200 miles off the African coast and was awaiting repatriation.

His wife was transferred to South Africa; she collapsed at a Johannesburg airport and died at a hospital, the South African Department of Health said.