Explainer
Andes Virus: The Only Hantavirus That Spreads Between People
Among the thirty-odd hantaviruses known to science, exactly one has ever been confirmed to jump from human to human. We look at how virologists proved it, and why it shouldn't be lumped in with the rest.
Almost everything you read about hantavirus is some variant of the same line: ‘the virus does not spread between people’. For decades that was unambiguously true. Hantaviruses are zoonoses; the reservoir is rodents; humans are dead-end hosts who inhale aerosolised waste. End of story.
Except for Andes virus. The exception is small enough that public-health agencies routinely omit it from prevention leaflets, but large enough that it now sits at the centre of an international outbreak investigation. Here is what makes Andes different.
El Bolsón, 1996: the moment the rule broke
In late 1996, the Patagonian town of El Bolsón experienced a cluster of severe respiratory illness with a striking signature: the cases were not just people who lived together, but doctors and nurses who had treated them. Several investigators flew in from Buenos Aires; some of them became patients.
Argentine virologists Ricardo Wainberg and Paula Padula reconstructed the outbreak and reached an inevitable conclusion: Andes virus had moved from person to person. It was the first documented case of human-to-human hantavirus transmission anywhere in the world.
How transmission actually happens
The mechanism is not particularly exotic. Person-to-person Andes virus transmission appears to require close, prolonged exposure to a symptomatic patient - household contact, intimate contact, or sustained healthcare without protective equipment. Transmission is thought to occur via:
- Respiratory droplets, particularly during the febrile prodromal phase
- Saliva and other secretions, including breastmilk
- Direct mucosal contact (kissing, sexual contact)
- Transplacental transmission in pregnancy, documented in case reports
What it does not appear to be is highly transmissible. Argentine researchers have estimated that only 2% to 5% of all Andes cases stem from person-to-person spread; the rest are still classic rodent exposures.
The ‘super-spreader’ question
A 2020 paper in the New England Journal of Medicine, analysing a 2018–19 outbreak in Epuyén, Argentina, introduced a phrase that has stuck: hantavirus super-spreaders. The investigators found that a minority of infected people - often those with high viral loads during a defined window - were responsible for most onward transmission events.
This is the same pattern observed in SARS, MERS and COVID-19. It is a useful concept for public health because it means quarantine and contact tracing are unusually effective: isolating the right person stops the chain.
Incubation: a four-to-forty-two day window
From exposure to first symptom, Andes virus can incubate anywhere from four days to six weeks. Person-to-person transmission tends to occur during the early prodromal phase. The wide window is what makes the MV Hondius outbreak hard to trace: a passenger who boarded in Ushuaia might not feel ill until they are several countries away.
Why this isn't COVID-19
A 38% case-fatality rate is terrifying, but a 38% case-fatality rate with limited person-to-person transmission is not a pandemic-shaped problem. Andes virus has been spreading in South America for at least thirty years without sparking a global event. The current outbreak is consequential precisely because it is unusual, not because it is repeatable at scale.
Editorial note
This article is intended as public information, not individual medical advice. If you are concerned about your symptoms, contact a qualified healthcare professional. We update outbreak reporting as new primary-source information becomes available.