Headlines this week have left people around the world wondering whether we’re on the verge of the next global pandemic. A cluster of hantavirus cases – usually spread only by wild rodents – was diagnosed on a trans-Atlantic cruise ship. As of May 8, the World Health Organization has confirmed eight cases and three deaths among the passengers and crew of the MV Hondius, which left Argentina in April.

The outbreak comes roughly a year after hantavirus was in the news for killing Betsy Arakawa, wife of actor Gene Hackman. Arakawa was likely exposed through contact with wild mice or rats on their property in Santa Fe, New Mexico.

Together, the two stories underscore that while hantavirus remains rare, it is not confined to remote jungles. Should you be worried? Should you put your summer travel plans on hold?

“No, I wouldn’t be worried,” said Jorge Salinas, MD, the medical director of infection prevention at Stanford Health Care. “If you’re going on a plane or a cruise this summer, I would say your risk of getting hantavirus is very close to zero.”

Salinas is an assistant professor of infectious disease and, before joining Stanford Medicine, he worked at the Centers for Disease Control and Prevention, where responding to emerging infections was central to his work. We asked him what people need to know about hantavirus.

1. Hantavirus mostly infects wild rodents

Hantavirus is a zoonotic infection, meaning it originates in animals but can cause disease in humans. Hantavirus has been detected in more than 100 species of mammals, including foxes and bats, but is primarily found in wild rodents, which can have persistent hantavirus infections without symptoms. In one recent study, about 3% of deer mice and white-footed mice across the United States tested positive for hantavirus, with geographic hotspots in Virginia, Colorado, and Texas.

People typically become infected with the virus by inhaling microscopic particles from these rodents’ urine, feces, or saliva – for instance, while cleaning a remote cabin infested with wild rodents. In the last 30 years, the CDC has logged 890 cases of hantavirus disease in humans, with 94% of cases west of the Mississippi and most occurring in Colorado, Arizona, or New Mexico.

Salinas was quick to point out that even in these high-risk states, house mice – the species you might see scurrying around a suburban garage or attic – are not the usual carriers of hantavirus.

“This virus is really one that’s found in wild rodents,” he said. “Infected animals might make their way inside a cabin in the mountains or a remote ranch, but we’re not typically seeing them in suburban or urban environments.”

2. This outbreak strain is unusual in its ability to spread between people

Hantavirus strains found in North America, including the strain that most likely killed Betsy Arakawa, don’t spread from person to person. Someone may become infected from rodents, but the virus ends there. The Andes virus, found in South America, is different; it is the only hantavirus documented to occasionally transmit between people. In 2018, the Andes strain of hantavirus spread throughout a small village in Argentina. Ultimately, the virus infected 34 people and caused 11 deaths.

But hantavirus, even the Andes strain, is not efficient at spreading between people.

“There are respiratory viruses like flu and COVID-19 that are incredibly efficient at transmitting person to person. That’s what they have evolved to do,” Salinas said. “Hantavirus just isn’t like that. It can jump to a few people after close contact with an infected, symptomatic individual, but we don’t expect it to spread very far.”

Data suggests that transmission between people requires close contact with someone who is already showing signs of infection. An analysis of the 2018 outbreak found that it began when one person, infected from a rodent, attended a birthday party of about 100 people. Over the following months, just three symptomatic individuals – attending other social gatherings while ill – drove all 34 infections.

In the end, the 2018 outbreak was contained through isolation and quarantine. More than 80 health care workers who had unprotected contact with patients were not infected, underscoring how inefficiently the Andes virus tends to jump between humans.

3. The disease can be deadly, and there is no vaccine

Rare as it is, hantavirus is not something to take lightly; its fatality rate is much higher than more common viruses such as influenza and COVID-19. Thirty-five percent of hantavirus cases in the U.S. in recent decades have led to death.

Early symptoms of hantavirus pulmonary syndrome – including fever, fatigue, and muscle aches – show up anywhere from 4 to 42 days after exposure and might be mistaken for the flu. But symptoms can rapidly progress to severe pneumonia and respiratory distress.

Researchers don’t fully understand how the virus causes such damage. Like the most severe COVID-19 cases, deaths from hantavirus may be due to an overactive immune response.

“It clearly affects the lungs,” Salinas said. “But it’s not clear how much of that is the virus attacking the lung cells versus the response of our body to the infection.”

There are no approved vaccines and no specific antiviral therapies proven effective against hantavirus. Patients who become sick can receive supplemental oxygen; mechanical ventilation; or, in the most severe cases, extracorporeal membrane oxygenation (ECMO), a machine that takes over the work of the heart and lungs while the body fights the infection.

“Because this virus is so rare, there just hasn’t been a whole lot of research into it,” Salinas said.

Data is sparse, for instance, on whether some groups of people – such as young children or elderly adults – are more likely to become severely ill, or whether some people are more likely to spread the virus.

4. Travel risk is negligible, but an N95 is smart in certain situations

Cruise ships and airplanes are not, under normal circumstances, places where anyone would expect to encounter hantavirus.

If you’re going on a plane or a cruise this summer, I would say your risk of getting hantavirus is very close to zero.

Jorge Salinas, MDMedical Director of Infection Prevention, Stanford Health Care

“If you asked me last month, I wouldn’t have predicted that we would see this on a cruise ship,” Salinas said. “I would still say that your risk of acquiring this particular rare infection on a plane or ship is very, very low.”

The outbreak required a specific and unlikely chain of events: A passenger had to be exposed to an infected rodent in Argentina, then board a ship where close quarters allowed the virus to spread. Salinas doesn’t expect that chain to repeat itself.

“Your risk of acquiring something else on a cruise is much higher,” he pointed out.

The picture looks slightly different for those heading into wilderness areas in the Western United States, where hantavirus circulates in wild rodent populations. If you’re planning on spending time in enclosed spaces where rodents may have nested – old cabins or hiking shelters, for instance – be mindful of disturbing rodent feces. If you’re sweeping out an area like this, Salinas recommended opening windows and wearing an N95 respirator – available at most hardware stores.

“It’s always a good thing to do in those situations,” he said, noting that the precaution guards against other diseases, not just hantavirus.

5. Hantavirus is part of a larger pattern

The list of diseases that have jumped from animals to humans – including hantavirus, Ebola, avian influenza, and COVID-19 – grows longer every year. About three-quarters of all emerging infectious diseases are zoonotic, and scientists expect that number to increase. That’s in part because humans are pushing deeper into wildlife habitats than in the past and because climate change is reshaping where animals live and breed.

“Given the way the world keeps changing and our populations are growing and moving, viruses will keep leaping from animals to humans,” Salinas said. “I expect this hantavirus outbreak to end, but it won’t be the last, and it’s a reminder that outbreaks can occur in unpredictable locations.”

Salinas sees the MV Hondius outbreak as a warning – and a reminder that we are never fully prepared for the next outbreak. The challenge, he said, is that the rarity of diseases like hantavirus has made them a low priority for research investment, leaving clinicians with no treatments or vaccines when outbreaks do occur.

“We should be investigating these diseases,” Salinas said. “That means investing in surveillance, in research, in understanding how these viruses move through animal populations before they reach us.”