BUENOS AIRES, Argentina (AP) — Officials and experts in Argentina are scrambling to determine if their country is the source of a deadly hantavirus outbreak that has gripped an Atlantic cruise.

The health emergency aboard the ship that’s moored across the ocean comes as Argentina sees a surge of hantavirus cases that many local public health researchers attribute to the recently accelerating effects of climate change. Argentina, where the cruise to Antarctica departed, is consistently ranked by the World Health Organization as having the highest incidence of the rare, rodent-borne disease in Latin America.

Higher temperatures expand the virus’ range because, in part, as it gets warmer and ecosystems change, rodents that carry the hantavirus can thrive in more places, experts say. People typically contract the virus from exposure to rodent droppings, urine or saliva.

“Argentina has become more tropical because of climate change, and that has brought disruptions, like dengue and yellow fever, but also new tropical plants that produce seeds for mice to proliferate,” said Hugo Pizzi, a prominent Argentine infectious disease specialist. “There is no doubt that as time goes by, the hantavirus is spreading more and more.”

The Argentine Health Ministry on Tuesday reported 101 hantavirus infections since June 2025, roughly double the caseload recorded over the same period the previous year.

A hantavirus found in South America, called the Andes virus, can cause a severe and often fatal lung disease called hantavirus pulmonary syndrome. The disease led to death in nearly a third of cases in the last year, Argentina’s Health Ministry said, up from an average mortality rate of 15 in the five years before that.

Hantavirus usually spreads by inhaling contaminated rodent droppings and can spread person-to-person, though that is rare, according to the WHO, whose top epidemic expert said the risk to the public is low. The Andes strain only hantavirus known to spread from human to human.

Authorities said passengers on the MV Hondius ship tested positive for the Andes virus. Argentina on Wednesday said it was sending genetic material from the Andes virus and testing equipment to help Spain, Senegal, South Africa, the Netherlands and the United Kingdom detect it.

The cause of infection remains under investigation

Argentine officials say they’re trying to pin down where infected passengers traveled in the country before boarding the Dutch-flagged cruise liner in Ushuaia, a city in southern Argentina known as the end of the world. Once they know the itineraries, they plan to trace contacts, isolate close contacts and actively monitor to prevent further spread.

The U.N. health agency, or WHO, says that the first death on board, a 70-year-old Dutch man, happened on April 11. His 69-year-old wife, also Dutch, died on April 26. The third passenger, a German woman, died on May 2.

The virus can incubate for between one and eight weeks. That makes it hard to know whether the passengers contracted the virus before leaving Argentina for Antarctica on April 1; during a scheduled stop to a remote South Atlantic island; or aboard the ship.

The province of Tierra del Fuego, where the vessel docked for weeks before departing, has never seen a case of hantavirus. Before boarding, the Dutch couple went sightseeing in Ushuaia, and traveled elsewhere in Argentina and Chile, WHO said.

The Argentine government’s leading hypothesis is that the couple contracted the virus during a bird-watching outing in Ushuaia, according to two investigators who spoke on condition of anonymity because they were not authorized to brief the media, with the investigation ongoing. Authorities are also tracing the Dutch tourists’ footsteps through the forested hillsides of Patagonia in southern Argentina where some infections are clustered.

Because early symptoms resemble the fever and chills of a flu, “tourists might think they just have a cold and not take it seriously. That makes it particularly dangerous,” Raul González Ittig, genetics professor at the National University of Córdoba and a researcher at state science body CONICET, said.

Climate change sends rodents to new frontiers

Argentina in recent years endured a historic drought. But it also had bouts of unexpectedly intense rainfall, part of a broader pattern of wild weather that scientists attribute to climate change.

Some of this variability has created conditions that have allowed hantavirus to flourish, experts say. Dry spells drive animals out of their usual habitats in search of food and water. Huge amounts of rain lead to vegetation growth, scattering seeds that attract leaf-munching rodents.

“When precipitation increases, food availability increases, rodent populations grow, and if there are infected rodents, the chance of transmission between rodents — and eventually to humans — also increases,” Ittig said.

Although hantavirus cases once were limited to the southern reaches of Patagonia, now 83% of cases are found in Argentina’s far north, according to the Health Ministry.

Argentina issued alerts early this year

The ministry issued an alert in January about several fatal outbreaks, including in the most populous province of Buenos Aires.

With rural hospitals underequipped, residents had no clue what hit them.

Daisy Morinigo and David Delgado said they initially thought their 14-year-old son had the flu when he came down with a fever and body aches. Doctors who first saw Rodrigo in the town of San Andrés de Giles sent him home with ibuprofen and orders to rest.

But the feisty fourth grader’s breathing worsened. On Jan. 1, they rushed Rodrigo to intensive care. He died just two hours after a hantavirus test came back positive.

“I wouldn’t wish this pain on anyone in the world,” Delgado said.