There are more than 50 known hantaviruses in the world. Every single one of them — except one — can only be transmitted from rodents to humans. That exception is the Andes virus, and it is the strain at the centre of the 2026 MV Hondius cruise ship outbreak. Understanding what makes Andes virus different from all other hantaviruses is key to understanding both why this outbreak is alarming and why scientists say the risk to the general public remains low.
The defining characteristic of Andes virus is its documented ability to spread from one infected human directly to another — a property called person-to-person transmission, or horizontal transmission. This was first confirmed during a cluster of cases in southern Argentina in 1996, when healthcare workers and close contacts of patients became ill without any known rodent exposure.
Subsequent outbreaks in Argentina and Chile — where Andes virus is endemic — have reinforced this finding. Studies of household clusters consistently show that spouses and caregivers of HPS patients have an elevated infection risk compared to the general population, even when controlling for shared environmental exposures.
No other hantavirus has produced credible evidence of person-to-person transmission in outbreak investigations or controlled studies.
The exact mechanism of Andes virus person-to-person transmission is still an area of active research, but the current scientific consensus points to respiratory droplets and potentially aerosols produced during close contact — particularly in shared sleeping spaces or during caregiving where face-to-face contact is prolonged.
Critically, casual contact does not appear to be sufficient. Studies of large social contacts of confirmed patients — workplaces, classrooms, social gatherings — have not produced secondary cases. The risk appears concentrated in:
Andes virus is endemic to the Patagonian region of Argentina and Chile, where its primary animal reservoir is the long-tailed pygmy rice rat (Oligoryzomys longicaudatus). This small rodent inhabits grasslands, agricultural areas, and forest edges at various altitudes throughout southern South America.
The virus has never been detected in rodent populations outside South America. Cases in other countries — including those seen in the MV Hondius outbreak — are exclusively travel-associated: people who were exposed in the endemic region and subsequently became ill after returning home or while in transit.
Andes virus causes Hantavirus Pulmonary Syndrome (HPS), the severe respiratory form of hantavirus disease. Its case fatality rate is approximately 25–35% in clinical settings with access to modern intensive care — slightly lower than the North American Sin Nombre virus (35–40%), but still among the highest fatality rates of any respiratory pathogen that circulates in the 21st century.
There is no approved antiviral, and no licensed vaccine. Treatment is supportive care in an ICU, with ECMO (extracorporeal membrane oxygenation) being the most effective intervention for patients in cardiopulmonary failure.
Despite its person-to-person transmission capability, Andes virus does not behave like an epidemic respiratory pathogen. Each known outbreak has remained self-limiting, with transmission chains typically ending after one or two generations of spread. The virus does not appear capable of sustained community transmission in the way influenza or SARS-CoV-2 can.
WHO's assessment of the 2026 MV Hondius outbreak reflects this: global risk is rated LOW for the general public. The outbreak is serious and requires careful contact tracing and monitoring of exposed passengers — but it does not represent a pandemic threat.
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