This story originally appeared in The Uptake, a weekly newsletter offering expert insights from the Bloomberg School of Public Health.
The voyage for the approximately 150 passengers on the MV Hondius, a Dutch ship on a weeks-long polar cruise, took a grim turn this week after an apparent outbreak of hantavirus—a rare rodent-borne infection—left three people dead and potentially sickened several more.
The World Health Organization has stressed that the risk to the public is low. "This is not the next COVID, but it is a serious infectious disease," Maria Van Kerkhove, the WHO's chief of Epidemic and Pandemic Preparedness and Prevention told the Associated Press. "Most people will never be exposed to this."
Still, the virus, and how it spread on a cruise ship, is raising questions.
What we know about the outbreak
Of the eight suspected cases so far, five have been confirmed as hantavirus, the WHO said on Wednesday, adding that the strain was the Andes virus—the only hantavirus in the Americas known to be transmitted between people, and not just from rodents to humans, Sabra Klein, a professor in the Department of Molecular Microbiology and Immunology at the Bloomberg School of Public Health, told The New York Times.
The Andes virus is endemic to Argentina, where the cruise embarked approximately five weeks ago. "The incubation period for hantavirus is one to eight weeks," says Kari Debbink, a teaching professor in Molecular Microbiology and Immunology. "The first two people (a Dutch couple) to pass away from the virus had traveled in Argentina before the cruise, suggesting that one or both may have been exposed prior to boarding the ship." But "it's unclear how much contact there was between those who got sick, so it's hard to say exactly how everyone was exposed."
Transmission of the Andes virus requires very close person-to-person contact, and hantaviruses are typically transmitted from rodents to humans by breathing in dust or air contaminated with particles from rodent feces, urine, or saliva or, less commonly, via bites or scratches.
The maritime setting makes this outbreak unusual: Unlike norovirus or foodborne illnesses, "hantavirus is not normally found on cruise ships," Debbink says.
About hantavirus
Though hantavirus infections are rare (there were only 890 confirmed cases reported in the U.S. between 1993 and 2023), they are often severe. Strains found in the U.S. and other parts of the Western Hemisphere—including the Andes virus—typically cause hantavirus pulmonary syndrome, a respiratory illness with a mortality rate of about 35%, according to the Centers for Disease Control and Prevention. The strains found in Europe, Asia, and Africa are more often associated with hemorrhagic fever and kidney complications, generally with lower mortality rates ranging from 1% to 15%.
Exposure to hantavirus doesn't always lead to illness, and many people who do become sick recover with supportive care, Klein told Science News. "[Fatalities are typically among] people who are older, who have other comorbidities that we know are associated with more severe respiratory illness."
Still, prevention is crucial, because while antivirals can help manage symptoms, there is no cure or vaccine for hantavirus infection, Klein told The New York Times in another article.
Preventing hantavirus infection involves avoiding contact with rodents and their droppings by sealing entry points, storing food securely, and safely controlling infestations without disturbing contaminated materials. If cleaning potentially affected areas, surfaces should be disinfected first and protective gear such as gloves and an N95 mask should be used to avoid inhaling particles, according to the CDC.
What happens next
The WHO is "currently working to answer many of the unanswered questions about where and how those who became ill were exposed to the virus," says Debbink. This includes contact tracing, looking for evidence of mice or mouse droppings aboard the cruise ship, and viral sequencing to identify the specific strain, possible vector species, and potential transmission routes.
Health officials in South Africa are tracing dozens of individuals who may have encountered infected cruise passengers and have identified 62 potential contacts; of those, 42 have been located and tested negative for hantavirus. The health ministry said in a report that the remaining 20 individuals are still being traced, and some may have already traveled abroad.
Throughout its journey the ship made multiple stops, including mainland Antarctica, the Falklands, South Georgia, Nightingale Island, Tristan, St. Helena, Ascension, and Cape Verde.
On May 6, Mónica García Gómez, Spain's health minister, said the Hondius is heading to Tenerife, where passengers will be allowed to disembark. Spanish citizens and anyone showing symptoms will be quarantined at a military base in Madrid, while asymptomatic passengers from other countries will be sent home.
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