The effort to monitor the spread of hantavirus from a cruise ship currently off the west coast of Africa is expanding, including in the United States, after health officials confirmed the virus on the ship is the rare strain that is transmissible from human to human.

Twelve countries are currently monitoring people who had disembarked the cruise ship before cases of hantavirus were confirmed, the World Health Organization said at a press conference Thursday. Those countries are Canada, Denmark, Germany, the Netherlands, New Zealand, Saint Kitts And Nevis, Singapore, Sweden, Switzerland, Turkey, the United Kingdom and the United States.

Two residents in Georgia and one in Virginia are among those being monitored for signs of the rare and often deadly disease after they returned home from the MV Hondius, the cruise ship at the center of the outbreak. All three are in good health and showing no signs of the virus, according to the departments of health in Georgia and Virginia. An unspecified number of California residents are also being monitored, the state's health department said, with none showing signs of the illness or infection.

But three people who were on the cruise have died, including a couple from the Netherlands and another woman from Germany, according to the World Health Organization. 

The husband in the Dutch couple died on board the cruise ship on April 11, the company said. However, Oceanwide Expeditions, the company that owns the ship, confirmed on Thursday that 30 guests — including six Americans — disembarked the Hondius on Saint Helena, an incredibly remote island in the middle of the South Atlantic, on April 24, and then returned on their own to their countries of origin.

"No samples were taken [from the man who died on board] and because his symptoms were similar to those of other respiratory diseases, hantavirus was not suspected," Dr. Tedros Adhanom Ghebreyesus, director-general of the WHO, said at a press conference Thursday.

Among those 30 who disembarked was the wife of the Dutch man who died on the cruise, according to Oceanwide Expeditions. Her health worsened on a flight from Saint Helena to Johannesburg on April 25, the WHO said. She then briefly boarded a KLM passenger flight in Johannesburg, but she was not allowed to fly due to her medical condition, the airline said. She died in South Africa the next day after not being allowed to fly home, according to the WHO.

A British man who exhibited symptoms on the ship was evacuated on April 27 to receive medical care in South Africa. His case was the first confirmed to be hantavirus on May 4, Oceanwide Expeditions said. The man remains hospitalized, but his condition was improving, the WHO said.

Officials then confirmed the Dutch woman's blood tested positive for hantavirus. KLM said it was notified of the test results on May 5 and was notifying everyone on the flight that the woman had boarded.

South African authorities said Wednesday the strain of hantavirus identified in the Dutch woman and the man in the hospital is the Andes strain. The Andes strain, which is found primarily in Argentina and Chile, can be transmitted from human to human, unlike other strains of the virus, which are caused by direct contact with rodents.

"In previous outbreaks of Andes virus, transmission between people has been associated with close and prolonged contact, particularly among household members, intimate partners and people providing medical care," Tedros said at the press conference. "That appears to be the case in the current situation."

Concerns over the virus

Health experts say the risk for a widespread outbreak of the disease is still unlikely. 

"The pandemic risk from this outbreak is low," said CBS News medical correspondent Dr. Céline Gounder. "Hantavirus does not spread the way flu or COVID does. But this is exactly the kind of event that tests whether global health systems work."

Two Brits who were aboard the Hondius have since independently returned to the U.K. and are also being monitored, according to the U.K. Health Security Agency. Neither is currently reporting symptoms, and they've been advised to self-isolate, the agency said in its statement, adding, "The risk to the general public remains very low." 

Another person who disembarked in Saint Helena was tested in Switzerland for the disease and tested positive for the Andes strain, the WHO said.

Three people with suspected hantavirus cases were airlifted from the ship Wednesday, including German and Dutch passengers and a British crew member, Oceanwide Expeditions said. The Dutch passenger and British crew member are being treated in the Netherlands and are both stable, the WHO said. The German passenger was asymptomatic and returned to Germany, the WHO said.

Dr. Jay Bhattacharya, acting director for the U.S. Centers for Disease Control and Prevention, said in a statement Wednesday night that the CDC has been "coordinating with domestic and international partners" since it learned of the outbreak.

The ship departed Cape Verde late Wednesday and is traveling north to the Canary Islands. The trip is expected to take three or four days, though some officials in the Canary Islands have already said they don't want the ship docking at the Spanish archipelago's largest island, Tenerife, as planned.

"I want to express my deep rejection of the arrival of the ship Hondius at the port of Granadilla," José Domingo Regalado, mayor of the Tenerife seaside community of Granadilla de Abona, said in Spanish in a video statement Wednesday. "What we ask is that action be taken, since they can be transferred to the nearest airport to their countries of origin so that they can quarantine and be treated by their health system if they require it."

Regalado added the decision to bring the passengers to the Canary Islands showed "no common sense."

Canarias President Fernando Clavijo announced on Thursday the ship would be allowed to anchor off the islands, but not dock there. 

Argentina offers help with treating virus

in Argentina, where the Andes strain originated, the country's health ministry said it was offering its "technical capacity, experience and resources available to assist health systems that require it."

"Yesterday it was confirmed that the variant corresponds to the Andes strain, which only has a history of circulation in Chubut, Río Negro and Neuquén and in southern Chile," the health ministry said. "Taking into account that the ship set sail from Argentina on April 1, our country actively collaborates with the international agencies involved and with all the countries involved to contain the outbreak and ensure proper management of cases."

The country said no associated cases have been reported in Argentina.

Argentina's health ministry also said no hantavirus cases have ever been reported in Tierro del Fuego since mandatory notification began in 1996. The cruise ship departed from that region's capital, Ushuaia.

The Dutch couple who died arrived in Argentina on Nov. 27 and spent months traveling around the country and neighboring Chile and Uruguay before returning to Argentina on March 27 and boarding the MV Hondius on April 1.

"Prior to boarding the ship, the first two cases had traveled through Argentina, Chile and Uruguay on a bird-watching trip, which included visits to sites where the species of rat that is known to carry Andes virus was present," Tedros said on Thursday. "WHO is working with health authorities in Argentina to understand the movements of the couple, and I thank the government of Argentina for its cooperation, given its experience and expertise with Andes virus."