Some California residents were among the 147 passengers and staff aboard a luxury cruise ship stricken by a suspected outbreak of hantavirus that has left three people dead and several others severely ill, officials confirmed Thursday.

California public health officials say they are monitoring the situation after being notified by the U.S. Centers for Disease Control and Prevention that some state residents were passengers on the MV Hondius. The precise status of those individuals, however, remains murky.

Hantavirus is a rare but deadly disease that attacks the lungs and is typically contracted by humans through inhalation of particles contaminated with the urine, feces or saliva of a wild rodent.

However, Dr. Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, confirmed Thursday that the Andes virus — a form of hantavirus that can spread from person to person — was involved in the outbreak.

Here’s what we know:

As its name suggests, the Andes virus is typically found in South America. The Dutch-flagged MV Hondius was on a 46-day journey that traveled from Antarctica with stops in Argentina.

In the case of human-to-human transmission, a person would first be infected by a wild rodent’s contaminated particles and then pass the infection to someone else, said Dr. Gaby Frank, director of the Johns Hopkins Special Pathogens Center.

“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,” Ghebreyesus said. “That appears to be the case in the current situation.”

None of the remaining passengers or crew members on the ship are symptomatic, he said.

The ship was not permitted to allow passengers to disembark at its original destination, Cape Verde, and is sailing for Spain’s Canary Islands.

“I want to be unequivocal here: This is not SARS-CoV-2. This is not the start of a COVID pandemic. This is an outbreak that we see on a ship. There’s a confined area,” Dr. Maria Van Kerkhove, who leads the WHO’s epidemic and pandemic management, said at a briefing. “This is not the same situation we were in six years ago. It doesn’t spread the same way like coronaviruses do.”

California passengers on the cruise

On April 1, 114 guests boarded the cruise ship in Ushuaia, Argentina. Twenty-three days later, 30 passengers — including six people from the United States — disembarked on a stop in St. Helena, a remote island about 1,100 miles off the coast of Africa, according to the cruise operator Oceanwide Expeditions.

Public health agencies in California, Georgia and Arizona were notified by the CDC that some of their residents were among the passengers on the cruise. It’s unclear whether these individuals disembarked on April 24, however.

The CDC is assisting local health authorities with monitoring California residents who were aboard the cruise, according to a statement by the California Department of Public Health on Friday.

As of Friday, one passenger has returned to their California residence and is in contact with local public health officials, and at least one other remains aboard the ship, according to the state agency.

“We understand that news of an unusual outbreak can be concerning,” said Dr. Erica Pan, director of the California Department of Public Health. “Unlike influenza and COVID-19, years of experience in South America have shown that this Andes hantavirus rarely spreads between people.”

Officials said the current public health protocol is to do daily symptom monitoring and reporting.

“As there are no known cases of Andes hantavirus infection from people without symptoms, and any spread has usually been limited to people with prolonged close contact with an ill person with this virus, the risk to the general public in California is extremely low,” the agency said in a statement.

In a statement earlier this week, the CDC also said that the risk to the American public “is extremely low” at this time.

“We urge all Americans aboard the ship to follow the guidance of health officials as we work to bring you home safely,” the agency said.

The others who exited the ship on April 24 were individuals from Canada, Denmark, Germany, the Netherlands, New Zealand, Switzerland, Sweden, Singapore, St. Kitts and Nevis, Turkey and the United Kingdom.

Of the remaining passengers still aboard the ship headed for Spain’s Canary Islands, California Department of Public Health said none were ill as of Friday.

How many people have been infected?

The number of lab-confirmed hantavirus cases has risen to five, according to the WHO. There are three additional suspected cases.

A timeline of reported cases of hantavirus aboard the cruise ship can be found here.

The WHO is monitoring reports of other people with symptoms “who may have had contact with one of the passengers. In each case, we are in close contact with the relevant authorities,” Tedros said.

The first passenger to have been infected, a Dutchman, became sick aboard the cruise ship on April 6 and died on April 11.

No samples were taken, because his symptoms were similar to other respiratory diseases. His widow left the ship with his body on April 24 during the scheduled stop at St. Helena.

“She deteriorated during a flight to Johannesburg on the 25th of April and died the next day,” Tedros said.

Before boarding the cruise ship, the Dutch couple 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.

After leaving the ship, the woman was briefly aboard a KLM aircraft in Johannesburg bound for Amsterdam but was barred from the flight due to her medical condition, the airline said in a statement.

Dutch news outlets reported that a flight attendant on a KLM airplane — who briefly had contact with the widow — started feeling sick and had mild symptoms and was in isolation at a hospital in Amsterdam.

The flight attendant has since tested negative for the Andes virus, Dr. Jeremy Faust, an emergency medicine physician, wrote on his Substack blog, Inside Medicine, citing a text message sent to him by Tedros.

“It is still possible that the flight attendant contracted the Andes virus. However, given our understanding of the virus, this information means that the flight attendant’s symptoms are not caused by the Andes hantavirus, but by some other medical illness,” Faust wrote.

More cases may be reported, because the incubation period — the time it takes between exposure to the virus and the onset of illness — for the Andes strain of the hantavirus is up to six weeks.

What we know about hantavirus

There are roughly 50 identified species of hantavirus. The virus that’s found in the Americas tends to cause a cardiopulmonary syndrome, a condition that affects the heart and the lungs, according to Frank.

There have been 890 laboratory-confirmed cases of hantavirus disease reported in the U.S. since surveillance began in 1993, according to the most recent data from the CDC.

From 1980 to 2025, 99 California residents have been diagnosed with a hantavirus infection, according to the California Department of Public Health.

CDC officials said 38% of people who develop respiratory symptoms may die from the disease.

Still, the data suggest that contracting hantavirus is rare, said Dr. Afif El-Hasan, member of the American Lung Assn.’s national board of directors.

There is no vaccine or specific antiviral medicine for hantavirius.

Intensive-care treatment may include intubation and oxygen therapy, fluid replacement and use of medications to lower blood pressure, according to the American Lung Assn.

The signs of hantavirus

Early symptoms of hantavirus are similar to the flu and include fatigue, fever and muscle aches, according to the CDC. Symptoms start to develop within one to eight weeks after contact with an infected rodent.

Half of those who contract the virus also experience headaches, dizziness, chills, nausea, vomiting, diarrhea and abdominal pain.

Four to 10 days after the initial phase of the illness, another round of symptoms can develop, which include coughing, shortness of breath and possible tightness in the chest as the lungs fill with fluid.

Even though contracting hantavirus in the U.S. continues to be a rare event, El-Hasan said, people should take these initial symptoms seriously and promptly seek medical care.

How to protect yourself

Hantavirus cases can occur year-round, but the peak seasons in the United States are the spring and summer, which coincide with the reproductive seasons for deer mice.

To lessen your risk of infection, keep wild rodents out of your home and other enclosed spaces by sealing any holes and placing snap traps.

If you find evidence of mice, wear personal protective equipment and disinfect the area. When you’re done, put everything, including cleaning materials, in a bag and toss it in your trash bin.