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The cruise ship departed Ushuaia, Argentina, in April with plans to ferry 147 passengers and crew members to some of the most remote places on earth, including Antarctica. But the ship, named the MV Hondius, had its voyage cut short by a rare virus that has killed three and infected several others. 

Hantaviruses are an ancient family of rodent-borne pathogens that likely caused disease in humans long before they first appeared in medical records in the 1950s. The viruses infect people via rodent waste—often through the inhalation of dust containing trace amounts of the excreta. Andes hantavirus, the strain that gripped the MV Hondius on its polar cruise, is one of a few hantaviruses known to cause hantavirus pulmonary syndrome, a rare but often deadly illness.

The Andes strain is also the only known hantavirus that can be transmitted human-to-human—a characteristic turning a rare rodent-borne infection into a multinational emergency, just a few years after the world was caught flat-footed by the COVID-19 pandemic.

The good news is that the Andes hantavirus, while uniquely deadly, is likely nowhere nearly as transmissible as COVID-19. Nevertheless, the outbreak is illuminating the complexity of responding to infectious disease outbreaks as international cooperation on public health issues has become fractured and contentious—all while global pandemics are only becoming more likely overall. A month before the first patients onboard the MV Hondius became symptomatic, Argentina officially completed the process of withdrawing from the World Health Organization, joining the United States in leaving a global health alliance that exists in large part to coordinate responses to these very kinds of cross-border disease outbreaks. 

The emergency also points to another growing challenge for global public health: Climate change is altering the rainfall, vegetation, and habitat conditions that influence rodent populations—changes that experts say boost the odds that the pathogens these animals carry will spill over into human populations.

While the hantavirus’s one-to-six-week incubation period means the outbreak could have originated in any of the passengers’ home countries, a possible culprit is the ship’s stop for a birding expedition near Ushuaia, which is home to a landfill that attracts rodents looking for food. Argentina’s health authorities have already documented a sharp rise in hantavirus this season: 101 infections have been recorded since June 2025, about twice as many as there were in the same period a year earlier.

The country’s health ministry hasn’t yet determined what’s behind the surge, but research suggests that climate change may play a role. Argentina and neighbouring countries in South America endured years of severe drought between 2021 and 2024, including Argentina’s worst dry spell in more than 60 years in 2023, followed by extreme rainfall last year. Weather extremes exacerbated by global warming change how rodents behave, according to Kirk Douglas, a senior scientist who studies hantaviruses and climate change at the University of the West Indies, Cave Hill, in Barbados.

Prolonged drought sends rats and mice into populated areas in search of food, which can put people at higher risk of contracting the virus. Sudden rainfall following drought causes trees and shrubs to produce a windfall of nuts and seeds, which tend to benefit rodents and boost their numbers—all the while increasing the risk of transmission from animal to human.

That doesn’t mean there’s a one-to-one relationship between global temperature rise and rodent-driven risk, however, and climate change is hardly the only force at play. A complex web of natural and human-made landscape changes can increase or decrease contact between humans and rodents. Increased temperatures and humidity, for example, don’t seem to influence the disease ecology of hantavirus in the same way that drought and precipitation do.

“Hantavirus is sensitive to the changes climate change will bring,” Douglas emphasized. “It’s all dependent on what the prevailing climate impact is.”

That complexity makes hantavirus risk difficult to predict—and easy to overlook. In the U.S., hantavirus has been rare since federal surveillance began in 1993. There were fewer than 1,000 total confirmed cases up to 2023, the latest year that data is available. About 35% of those cases, almost all of which occurred west of the Mississippi River, resulted in death. 

As in South America, the dynamics of hantavirus in the U.S. may be shifting. The places most at risk, federal scientists reported in a study published last year, are dry landscapes where homes are spread out, many kinds of rodents live nearby, and communities may have fewer resources to prevent or respond to disease—conditions that describe broad swaths of the American West.