Spain has agreed to "welcome" the cruise ship at the center of a rare hantavirus outbreak, with three people now dead after catching the illness onboard, according to the World Health Organization.

The ship, with nearly 150 people aboard, had been awaiting help off the coast of Cape Verde in the Atlantic Ocean after the African island refused to let it dock over public health concerns. 

Besides the three fatalities – two of whom died on board and a third who died shortly after disembarking – there are four other suspected or confirmed cases of the virus, one of whom is a British national who was evacuated from the boat and is now in intensive care in South Africa, according to the WHO.

The WHO says it suspects there has been some human-to-human transmission on the stricken ship, where passengers have been told to remain in their cabins as much as possible. It has also begun tracking down people who shared a flight with a 69-year-old passenger.

The Dutch woman, whose husband died onboard two weeks earlier, got off the boat with "gastrointestinal symptoms" on April 24 and died two days later, after her condition "deteriorated during a flight to Johannesburg," the WHO said. "Contact tracing for passengers on the flight has been initiated," it added.

On Tuesday, the WHO's epidemic and pandemic preparedness and prevention director, Maria Van Kerkhove, told journalists Spanish authorities "have said that they will welcome the ship to do a full investigation, a full epidemiologic investigation, full disinfection of the ship and of course ... assess the risk of the passengers that are actually on board."

The agency said Tuesday that it's current plan is to evacuate two sick passengers to the Netherlands, then for the ship to continue on to Spain's Canary Islands.

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 Cape Verde, off the West Africa coast. But no one was allowed to disembark, Netherlands-based operator Oceanwide Expeditions said.

Cape Verde's Health Ministry said Monday that it would not allow the ship to dock because of public health concerns, adding 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, but when humans catch the virus, it has a mortality rate of up to 50%.

It was unclear how the outbreak could have started, and WHO said it was investigating while working to coordinate the evacuation of two sick crew members. Another sick person - the British man evacuated to South Africa on April 27 - tested positive for the virus, authorities said. He is in critical condition, health officials 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, 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.

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.

"It's been very tricky for Cape Verdean authorities," Lindstrand said. "What they have to deal with is a public health event. And of course, they have been thinking about the protection of the population here."

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

The ship left Ushuaia in southern Argentina on April 1, according to Argentine provincial authorities. Health officials there said they confirmed no passengers had hantavirus symptoms when the Hondius departed.

But because symptoms can appear up to eight weeks after exposure, "the passengers could have been incubating the disease if they acquired it within the country or elsewhere in the world," Juan Facundo Petrina, director of epidemiology for Tierra del Fuego province, told AP in an interview from Ushuaia.

He noted that the province hasn't historically seen hantavirus cases, but infections have broken out in other Argentine provinces, leading to 28 deaths nationwide last year, according to the health ministry.

Oceanwide Expeditions advertises 33-night or 43-night "Atlantic Odyssey" cruises on the vessel.

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