What is hantavirus?
An educational overview of hantaviruses — what they are, how they spread, and why the 2026 outbreak attracted international attention.
A family of viruses carried by rodents
Hantaviruses are a genus of RNA viruses belonging to the family Hantaviridae. They are zoonotic pathogens — meaning they circulate naturally in animal populations and occasionally spill over into humans. Each hantavirus species has a specific rodent reservoir host: a particular species of mouse, rat, or vole in which the virus persists without causing visible illness.
More than 50 distinct hantavirus species have been identified worldwide. The vast majority of human infections result from inhaling microscopic particles — aerosols — generated by dried rodent droppings, urine, or nesting material. This can happen during routine activities: sweeping an old shed, working in a barn, camping in rodent-infested areas, or cleaning a space that has been unoccupied for some time.
Person-to-person transmission is rare with almost all hantavirus species — a critical feature that makes these outbreaks manageable compared to directly transmissible pathogens. The significant exception is Andes orthohantavirus, the only hantavirus with documented human-to-human spread, which is the strain involved in the 2026 MV Hondius cluster.
Two main disease patterns
When hantaviruses cause illness in humans, they typically produce one of two distinct clinical syndromes depending on the viral species and geographic region:
How transmission actually happens
Understanding transmission routes helps clarify both the risk and why hantavirus outbreaks are relatively uncommon despite the viruses being widely distributed among rodent populations.
The primary route is inhalation of infectious aerosols. When infected rodents excrete virus in urine, faeces or saliva — and these deposits dry out — disturbing them (sweeping, digging, handling nesting material) can aerosolise viral particles. These particles are small enough to reach deep lung tissue when inhaled.
Transmission can also occur through a bite from an infected rodent, or through direct contact between broken skin or mucous membranes and infected material — though these routes account for a small proportion of reported cases. There is no evidence that hantaviruses spread through food preparation, cooking, or consuming rodent-contaminated food, though hygiene is obviously important.
The Andes virus stands apart because of documented limited human-to-human spread, thought to occur through close contact with an infected person during the prodromal (early) phase of illness — particularly in household and care settings. This is why the cluster pattern aboard a contained environment like the MV Hondius was of particular public health concern.
Geographic distribution
Hantaviruses are found on every inhabited continent. Their geographic range broadly follows the distribution of their reservoir rodent species.
In the Americas, HPS cases are concentrated in Argentina, Chile, Brazil, and the south-western United States. The Andes virus circulates in the long-tailed pygmy rice rat (Oligoryzomys longicaudatus) across Patagonia, the Andes foothills, and sub-Antarctic islands — precisely the regions visited by the MV Hondius during its April 2026 expedition.
In Europe, Puumala virus (bank vole reservoir) causes seasonal outbreaks of nephropathia epidemica across Scandinavia, Finland, and central Europe. Dobrava virus is present in the Balkans. Seoul virus — unusual in being carried by the common brown rat (Rattus norvegicus) — has a near-global distribution but rarely causes severe disease.
In Asia, Hantaan virus (striped field mouse) causes the most severe form of HFRS, predominantly in China, South Korea and Russia. Seoul virus is also common across Asia.
Why the 2026 outbreak was unusual
Hantavirus cases in travellers are rare — most infections occur in people with occupational or residential exposure to rodent habitats. The MV Hondius cluster stood out for several reasons.
First, the vessel visited South Georgia, Nightingale Island, and Tristan da Cunha — remote sub-Antarctic islands with high rodent density and documented Andes virus reservoir hosts, but typically limited human access. Multiple wet landings in these environments created aerosolisation risk during shore activities.
Second, the cluster pattern — multiple cases among passengers from different countries on the same vessel — raised the question of whether Andes virus human-to-human transmission had occurred on board. WHO's genomic sequencing (DON599) confirmed Andes orthohantavirus in all three fatal cases.
Third, the international scope — 147 people from 23 nationalities — meant potential cases could surface in many countries after disembarkation. This triggered coordinated international contact tracing across Europe, North America, and South America.
See the full MV Hondius outbreak investigation →