Andes virus: the only hantavirus that spreads between people

Most hantaviruses obey a simple rule: the virus circulates in a single species of rodent, the rodent excretes virus in its urine and droppings, and humans are infected when they inhale the dried particles. Once a human is sick, the chain stops there. The Andes virus is the exception.

A South American discovery

Andes virus was identified in 1995 in southern Argentina and Chile. The natural reservoir is the long-tailed pygmy rice rat, Oligoryzomys longicaudatus, which is widespread in the temperate forests and steppes of Patagonia. Like other New World hantaviruses, Andes virus causes hantavirus pulmonary syndrome (HPS), a severe disease in which capillary leak in the lungs can lead to acute respiratory distress and circulatory collapse.

The case fatality rate of HPS caused by Andes virus is in the range of 25–40 % — comparable to Sin Nombre virus in North America, and on the same order of magnitude as the early estimates for the MV Hondius cluster.

Why the human-to-human story is different

Standard hantavirus transmission is shown below: rodent excretes virus, particles dry out, humans inhale them.

The first credible evidence of person-to-person transmission came from an outbreak in El Bolsón, Argentina, in 1996. Investigators traced cases among people who had had close contact with a sick patient — but no rodent exposure of their own. Subsequent epidemiological work in Chile in the early 2000s and again in 2018 reinforced the pattern. Sexual partners, household members, and healthcare workers caring for sick patients without adequate protection were over-represented among secondary cases.

Critically, person-to-person transmission has only ever been documented for the Andes virus, and only under conditions of close, prolonged contact. There is no evidence of casual airborne transmission such as that seen with influenza or SARS. WHO summarises the public risk from Andes-virus events as low.

Where Andes ranks among hantaviruses

Compared to its cousins, Andes virus is severe but rare:

What this means for the MV Hondius

Several elements of the MV Hondius cluster are consistent with Andes-virus epidemiology:

• The voyage originated in Ushuaia, the southernmost city of Argentina, deep within the natural range of the rodent reservoir. Pre-boarding rodent exposure during provisioning, embarkation logistics, or shore excursions in nearby protected areas is biologically plausible.
• A Swiss passenger tested positive for the Andes strain after disembarking and returning home, providing the first laboratory confirmation in the cluster.
• The geographic dispersion of subsequent cases — including a Dutch passenger who died in Johannesburg, a British passenger evacuated to South Africa, and a French contact case identified during an air-evacuation flight — is consistent with the long, variable incubation period of HPS (1–8 weeks after exposure).

Whether onboard human-to-human transmission has occurred is the central question for sequencing and contact-tracing teams. If multiple cases share an identical viral genome but none could plausibly have been exposed to rodents independently, that would be a significant finding.

Treatment and prevention

There is no licensed antiviral therapy for Andes-virus disease in Europe or North America. Care is supportive: oxygen, fluid management, and intensive care including mechanical ventilation in severe cases. Early hospitalisation significantly improves outcomes — patients who reach a critical care unit before the cardiopulmonary phase fare better than those who present late.

Prevention focuses on rodent contact: securing food storage, sealing entry points in cabins and outbuildings, and using N95/FFP2 respirators plus nitrile gloves when cleaning rodent-infested spaces. For travellers to Patagonia, Chile and the sub-Antarctic, standard advice is to avoid disturbing dust in unventilated cabins and shelters where rodents may have been active.