Human-to-human transmission of killer hantavirus suspected in cruise ship outbreak. Here’s what that means

Human-to-human hantavirus transmission system may feature occurred betwixt come together contacts on ship, WHO official says

After a spate of deaths and illnesses stemming from a hantavirus outbreak on a cruise ship, health officials now suspect human-to-human transmission may have played a role in the spread of this potentially deadly infection.

Investigators are also racing to identify whether the virus strain involved in the MV Hondius crisis is one known for higher death rates and prior instances of transmission between people.

"Some of the cases had very close contact with each other, and certainly human-to-human transmission can't be ruled out, so as a precaution, this is what we are assuming," Dr. Maria Van Kerkhove, director of epidemic and pandemic preparedness and prevention at the World Health Organization (WHO), told reporters on Tuesday in Geneva.

While those possibilities might call to mind the early days of the COVID-19 pandemic — and the potential for broader spread of this rare, rodent-borne disease — scientists have been quick to stress that hantavirus is not a major global threat.

"People really do need to understand that there are different degrees of person-to-person transmission," said Angela Rasmussen, a virologist with the University of Saskatchewan's Vaccine and Infectious Disease Organization. 

There are also many different variants of this virus, one of which is found in Argentina, where the cruise began. That strain has been linked to transmission among individuals in hospital settings, but those instances remain infrequent and isolated, Rasmussen stressed.

"So this virus — right now anyways — doesn't seem to be as big of a risk as something like flu."

At least seven people out of roughly 150 passengers and crew on the Dutch-flagged MV Hondius have fallen ill at different times along the ship's month-long journey to remote islands throughout the Atlantic Ocean.

All seven are now suspected hantavirus cases, with two infections officially confirmed so far, WHO said. Four Canadians are also on board the stranded ship as it waits in the waters off the West African nation of Cape Verde, but there are no reports of infection among those individuals.

Symptoms among infected passengers and crew have included fever, gastrointestinal impacts and a rapid progression to pneumonia, acute respiratory distress syndrome and shock — with individuals having an onset of illness at different points between April 6 and April 28, noted WHO’s latest situation report.

Three people are now dead, namely a German passenger and a Dutch couple. The couple fell ill at different times, with the man dying on board the ship on April 11 and his wife passing away in hospital in South Africa after falling ill on a flight to Johannesburg. WHO is contact tracing passengers from that flight, the organization said.

Several individuals on the Hondius are still awaiting evacuation, including two people who need "urgent medical care," and an individual linked to one of the passengers who died, the company behind the luxury cruise expedition said on Tuesday. Two specialized aircraft are now en route to Cape Verde to help with those evacuations, reads the latest update from Oceanwide Expeditions.

The risk to the general public remains low, WHO's Van Kerkhove said. Any possible human-to-human transmission would have occurred between very close contacts like married couples, she said.

More typically, humans catch hantavirus directly from infected mice or rats — or by inhaling their droppings — and it doesn't transmit further.

"This is not a virus that spreads like flu or like COVID," Van Kerkhove said. "It's quite different."

Among the sick, a British individual who was the first passenger to test positive for hantavirus remains in intensive care at a hospital in South Africa.

Based on the group's travel history to Argentina, tests are underway to confirm if the passenger had the South American virus variant, said Nazir Ismail, executive director of South Africa’s National Institute of Communicable Diseases.

That strain, known as the Andes variant, is among the "New World" variants found across the Americas, which can cause severe disease known as hantavirus pulmonary syndrome (HPS).

While symptoms might not appear for weeks, the condition can eventually escalate quickly, leading to severe respiratory failure with a death rate of roughly 40 per cent.

The Andes variant is also unique for causing instances of transmission between people.

"Although uncommon, limited human‑to‑human transmission of HPS due to Andes virus has been reported in community settings involving close and prolonged contact. Secondary infections among healthcare workers have been previously documented in healthcare facilities, though remain rare,” WHO said in its situation report.

Cruise ship passengers sick with hantavirus possibly infected off the vessel: WHO

A medical journal article from 1997, for instance, documented a cluster of 20 Andes virus cases in southern Argentina, including multiple physicians who were directly involved in caring for patients with severe hantavirus infections.

"Epidemiologic links between all but four of the cases and evidence of low rodent population density in the area strongly suggest person-to-person transmission ... During this outbreak," the research team noted.

A later paper, published in June 2025, discussed another Andes virus outbreak in the village of Epuyén, in southern Argentina, seven years prior.

"The strain demonstrated a high capacity for sustained transmission among the human population requiring the implementation of quarantine measures, rigorous contact tracing, isolation of close contacts, and active clinical monitoring to prevent further spread," those researchers wrote.

Last December, WHO's Americas branch also warned that human hantavirus infections were rising in the region, particularly in Bolivia, Brazil and Argentina, along with a spike in deaths.

Argentina reported more than 60 cases of hantavirus pulmonary syndrome last year, with a 32 per cent death rate — a rise from an average mortality rate of 15 per cent in the four years prior.

"Old World" hantaviruses, in contrast, are found in Europe and Asia and typically have a much lower death rate linked to hemorrhagic fever with renal syndrome, involving kidney failure and internal bleeding.

While scientists will be closely watching the spread of the Andes strain of this virus, infections of all kinds of hantavirus are extraordinarily rare, and human-to-human transmission remains even less frequent.

So why did so many people get sick back-to-back from such a rare virus on the MV Hondius?

Rasmussen, from the University of Saskatchewan, said it's not entirely unexpected that a cluster of hantavirus infections could emerge within the close confines of a cruise ship — either from someone first getting infected in Argentina and bringing the virus on board or multiple infections linked to rodents on the ship itself.

WATCH | Cruise ship stranded at sea due to deadly suspected hantavirus outbreak:

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The distinct environments of these ships can, unfortunately, help facilitate the spread of viral infections, Rasmussen said. "Cruise ships are environments where people are isolated in one spot. They share common infrastructure, like plumbing ... They share common air and indoor spaces."

Norovirus, known for causing short-lived gastrointestinal illness, is a frequent source of cruise ship outbreaks. And in 2020, a crisis involving hundreds of cases of COVID-19 on a cruise also made headlines in the early days of the pandemic.

Rasmussen said this unprecedented hantavirus outbreak offers a reminder that it's circulating in rodent populations everywhere, including many parts of Canada — which poses a far bigger risk to Canadians than a cluster of infections on a cruise.

"Wear a respirator while you're sweeping out any old mouse droppings, because you don't want to breathe in those inhaled aerosols," she warned.

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