Hantavirus is suspected of spreading aboard a luxury cruise ship, killing three passengers and sparking new concerns as a once obscure disease, with an extraordinarily high death rate, rises amid changing climate conditions.

Officials are still trying to determine what happened aboard the ship, which commands fares of up to $28,845 for a 46-day journey that includes a tour of the Antarctica Peninsula and stops in Tierra del Fuego on the southern edge of Argentina.

In addition to the three deaths, a fourth passenger was evacuated to a South African hospital and was in intensive care, and two crew members fell ill. The Dutch-flagged ship remained off the coast of Cape Verde, an island nation about 400 miles west of Senegal, where it was scheduled to have docked on Monday.

Hantavirus is fairly rare in the Americas, but its high case fatality rate makes it a disease of major public health concern, the World Health Organization says. Hantavirus is more common in Asia and Europe, where the strains that circulate are less deadly, with a case fatality rate that ranges from less than 1% to 15%.

Hantavirus is most commonly spread by inhaling particles contaminated with the virus — such as dried mouse urine, saliva or droppings.

But there is one strain of hantavirus — known as the Andes virus — that can be transmitted from human to human, and has been transmitted in Thailand and Argentina.

It’s unclear what strain of hantavirus hit the ship.

The first death on the ship occurred on April 11 somewhere in the Atlantic Ocean, and the man’s cause of death couldn’t be determined on board, the ship operator said. The body was transported off the ship April 24 as the vessel docked on Saint Helena Island, about 1,100 miles off Africa, and the man’s wife accompanied his remains.

The wife became unwell on the trip home and later died. The cruise ship operator was notified of the woman’s death April 27. The couple were Dutch nationals. On the same day, another passenger, a British national, became seriously ill on the ship and was medically evacuated to South Africa. That patient was confirmed to have hantavirus.

A German passenger died aboard the ship on Saturday. And on Monday, the ship operator said two crew members — one British, one Dutch — had acute respiratory symptoms, one mild and one severe but both requiring urgent medical care.

Among the possibilities that could explain the suspected outbreak, according to Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert, are rodents getting on board the ship and exposing people to the virus, or person-to-person transmission.

“Could a cruise member have been cleaning up an area and incidentally aerosolized some rodent droppings?” said Dr. Elizabeth Hudson, regional physician chief of infectious diseases at Kaiser Permanente Southern California. “Was there a shore excursion that the passengers and crew attended where they were exposed to aerosolized rodent droppings?”

Because hantavirus is so rare, it’s hard to say what effect these deaths might have on the cruise industry. COVID-19 hit the industry hard, but that was a global pandemic with a virus spreading rapidly with human-to-human contact. A key question for investigators is how the virus spread.

The MV Hondius is operated by Oceanwide Expeditions, which has a fleet of four ships and bills itself as a cruise ship eco-tour operator with trips to the Arctic and Antarctica. The Hondius can hold 170 passengers in 80 cabins.

As of Monday, there were 148 people on board, including 17 U.S. passengers. One deceased passenger remained on board.

The MV Hondius sailed on March 20 from Ushuaia, the capital of Tierra del Fuego on the southern edge of Argentina, on a round trip to the Antarctica Peninsula, returning to port 11 days later. On April 1, the ship left Argentina and headed back to Cape Verde, with stops on the Atlantic Ocean islands of South Georgia, Tristan de Cunha and St. Helena.

The strains of hantavirus in the Americas are attracted to the small blood vessels of the lungs and make the blood vessels leaky — which is bad, because the lungs need air, said Chin-Hong.

“So people can’t breathe,” he said. “It’s like you’re drowning. The lungs are leaky, so the fluid fills up in the lungs.”

There are 50 species of hantavirus. The virus that’s found in the Americas tends to cause a cardiopulmonary syndrome, a condition that affects both the heart and the lungs, said Dr. Gaby Frank, director of Johns Hopkins Special Pathogens Center.

Hantavirus is associated with a case fatality rate of up to 50% in the Americas. It was the cause of death of Gene Hackman’s 65-year-old wife, Betsy Arakawa, in their Santa Fe, N.M., home. Arakawa died days before Hackman, 95, died as a result of heart disease. There were signs of rodent entry in some structures on the couple’s property. Last year, three people in Mammoth Lakes died after contracting hantavirus. There was evidence of mice where all three of the deceased had worked, and one person had numerous mice in their home, according to the public health office for Mono County, home to Mammoth Lakes.

There is no vaccine or specific antiviral medicine for hantavirus. In the Americas, doctors can help infected people by putting them on a life-support machine known as ECMO, for extracorporeal membrane oxygenation, which breathes for the patient by oxygenating the blood. “It’s very, very intensive, and that’s why the fatality rate is so high,” Chin-Hong said.

Some experts expect hantavirus to be more of a concern in the future in some parts of the world due to climate change as rising temperatures are favorable to animals and insects that carry diseases, such as the increase in Lyme disease as the climate becomes more hospitable to the ticks that transmit it.

With rainfall patterns changing as global temperatures warm, “then you would expect that the rodent population will increase with time,” Chin-Hong said. with climate change over time, then you would expect that the rodent population will increase with time,” Chin-Hong said. Examples include people being sickened with, and dying from, rat-borne diseases such as leptospirosis after Hurricane Maria hit Puerto Rico in 2017.

In the U.S., there’s an average of 30 hantavirus cases reported a year, a figure that has remained relatively steady. But “there has been more media attention to it,” said Hudson.

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(Times staff writer Karen Garcia contributed to this report.)

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