Of the approximately 50 known hantavirus species, only one — Andes virus (ANDV) — has repeatedly demonstrated the ability to spread directly from one human to another. This single property transforms it from a rodent-borne pathogen of regional concern into a potential global health threat, and it is the central reason why the MV Hondius cluster has drawn such intense WHO scrutiny.
The Standard Rule: Rodents to Humans Only
All hantaviruses share a common transmission model. The virus lives in the kidneys, lungs, and saliva of specific rodent reservoirs — different species in different parts of the world — without causing disease in those animals. The virus is shed continuously in urine, faeces and saliva.
Humans are infected when they inhale aerosolised particles of contaminated rodent excreta, typically in enclosed or poorly ventilated spaces: attics, barns, cabins, or — in rare cases — field sites. Bites can transmit the virus but are uncommon. Once a human is infected, the standard scientific consensus, confirmed for all hantaviruses except ANDV, is that the chain stops there. No onward human transmission occurs.
This makes hantavirus fundamentally different from influenza, SARS-CoV-2, or Ebola, where human-to-human chains sustain outbreaks independently of the animal reservoir.
Where Andes Virus Breaks the Rule
Andes virus circulates primarily in Argentina and Chile, with the long-tailed pygmy rice rat (Oligoryzomys longicaudatus) as its principal reservoir. The virus causes Hantavirus Pulmonary Syndrome (HPS) with a case fatality rate of 35–40%, the highest of any hantavirus strain.
The first strong epidemiological evidence for person-to-person transmission came from a 1996 cluster in southern Argentina, where 16 cases were linked in chains that could not be explained by shared rodent exposure. Several cases were healthcare workers or family members of index patients who had no other plausible source of infection.
Since then, multiple outbreaks — notably in El Bolsón, Argentina (2011) and in southern Chile — have produced contact clusters where person-to-person spread could not be ruled out, and in some cases was the only plausible explanation.
The Mechanism: Still Not Fully Understood
Despite nearly three decades of research since the 1996 cluster, the precise mechanism by which Andes virus achieves person-to-person spread remains poorly characterised. Several hypotheses have been investigated:
Respiratory aerosol: High viral loads in respiratory secretions of severely ill patients could theoretically generate infectious aerosol, particularly during the acute pulmonary phase. This is the most widely accepted hypothesis.
Direct contact: Exposure to blood or other bodily fluids of an acute patient during caregiving. This route is consistent with the family-member and healthcare-worker cases seen in Argentine clusters.
Fomite transmission: The virus can survive on surfaces for several hours under the right conditions, though there is no direct epidemiological evidence this route is significant.
What is consistently true across documented person-to-person clusters is that transmission appears to require prolonged, close contact — typically within the same household or clinical care setting — and does not produce the exponential community spread seen with respiratory viruses.
Why the MV Hondius Cluster Is Scientifically Important
The Hondius cluster presents a unique natural experiment. Approximately 280 people shared a confined vessel for up to 21 days. The exposure history of every passenger and crew member is documented through the ship’s manifest. And crucially, the Antarctic landscape offers extremely limited opportunities for rodent exposure under normal circumstances.
If genomic analysis of the eight confirmed cases demonstrates that all viruses are phylogenetically linked in a chain rather than sharing a common source strain, that would constitute strong evidence that at least some transmission occurred person-to-person aboard the vessel, rather than during shore excursions.
Conversely, if all cases carry genetically identical virus pointing to a single exposure event — perhaps a contaminated food store that harboured an infected rodent — the rodent-source hypothesis would be better supported.
WHO’s preliminary findings released May 11 note “limited but not conclusive” evidence of person-to-person spread. The phrase is carefully worded: the epidemiology is suggestive but the genomics are not yet definitive.
Implications If Person-to-Person Spread Is Confirmed
Clinical management: If Andes virus can reliably spread via the respiratory route, healthcare workers treating HPS patients would need N95 or higher respiratory protection, airborne infection isolation rooms, and the same infrastructure used for tuberculosis or novel influenza. Currently, standard droplet precautions are recommended, but this guidance is under review.
Outbreak response: A confirmed person-to-person Andes virus cluster would, for the first time, require contact tracing methodologies analogous to those used for respiratory pathogens — far more complex and resource-intensive than current rodent-exposure investigations.
Travel medicine: Visitors to endemic regions in Patagonia and southern Chile currently receive guidance focused on avoiding rodent habitats. If person-to-person spread in household settings is accepted, the guidance for caregivers and household contacts of suspected cases would need substantial revision.
Research priority: Despite its uniqueness, Andes virus has received comparatively limited research funding relative to SARS-CoV-2 or Ebola. The Hondius cluster will likely shift that calculation significantly.
What You Should Know Right Now
For the general public not travelling to endemic regions, Andes virus person-to-person spread poses no practical risk. The documented transmission events all involve intimate or caregiving contact with severely ill patients.
For travellers to Argentina, Chile and adjacent Andean countries, the key risk remains rodent exposure in rural and semi-rural settings. Avoiding rodent-infested cabins, wearing N95 masks when cleaning enclosed spaces, and seeking immediate medical attention for fever and respiratory symptoms after potential exposure remains the evidence-based protective strategy.
For those who were aboard MV Hondius or in close contact with a confirmed case, follow the monitoring guidance of your national health authority precisely. If you develop fever, headache, muscle aches or respiratory symptoms within 45 days of exposure, seek emergency care immediately and inform clinicians of your exposure history.
Track the latest case data on the global outbreak map and check the symptoms guide for full clinical detail.
Sources
- Peters CJ et al. (2002). Hantavirus pulmonary syndrome: the new American hemorrhagic fever. Clinical Infectious Diseases.
- Padula PJ et al. (1998). Hantavirus pulmonary syndrome outbreak in Argentina. Lancet.
- WHO Hantavirus Fact Sheet
- CDC Andes Virus Information
- ECDC MV Hondius Rapid Risk Assessment
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