Science explainer

The content for the "about the virus" section of the site. Plain language, no jargon-as-drama.

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What is hantavirus?

Hantaviruses are a family of viruses carried by rodents. Different strains exist on different continents and cause different illnesses. The two main diseases hantaviruses cause in humans are hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). The strain involved in the MV Hondius outbreak is Andes orthohantavirus, which causes HPS.

Hantaviruses have been studied seriously since 1993, when an outbreak in the Four Corners region of the United States led to the identification of Sin Nombre virus. Before that, hantaviruses were known mainly from a Korean War outbreak in the 1950s that killed thousands of UN soldiers.

How does it usually spread?

In the vast majority of cases, people catch hantavirus by inhaling dust that has been contaminated with the urine, droppings, or saliva of infected rodents. This typically happens in enclosed spaces — cabins, sheds, barns, basements — where a rodent infestation has gone unnoticed and dried droppings get kicked up into the air.

Direct rodent bites and contact with contaminated surfaces can also cause infection, but airborne dust is the main route.

Why is the Andes virus different?

The Andes virus is the only hantavirus strain ever documented to spread directly from person to person. Every other strain dead-ends in humans — you can catch it from a rodent but you can't pass it to another person. Andes virus, found mainly in southern Argentina and Chile, has been linked to small clusters of person-to-person transmission, typically among family members and healthcare workers caring for sick patients.

This is what makes the MV Hondius outbreak unusual. The ship is believed to have picked up Andes virus exposure in southern Argentina or aboard during its time in those waters, and then human-to-human spread occurred among passengers and crew in close quarters.

Symptoms

Andes virus infection has two phases.

The first phase — fever, headache, muscle aches, chills, sometimes diarrhea or nausea — looks like the flu. It typically begins 7 to 39 days after exposure and lasts 4 to 10 days.

The second phase comes on suddenly. Fluid builds up in the lungs (pulmonary edema) and breathing becomes very difficult. Patients often need ventilator support. This phase is when most deaths occur.

The case fatality rate for HPS caused by Andes virus is roughly 35 to 40 percent. There is no specific antiviral treatment. Care is supportive — oxygen, fluids, blood pressure management, and ventilator support when needed.

How worried should the public be?

The World Health Organization continues to assess the risk to the general public as low. The outbreak is contained to the MV Hondius and known close contacts of passengers, all of whom are under medical observation.

Andes virus is rare outside its natural range in southern South America. Casual contact with someone who has recovered does not transmit the virus — it spreads only during the symptomatic phase, mainly through respiratory droplets and possibly through bodily fluids in very close contact.

Prevention

For people not in the affected group, no special action is needed.

For people working with rodents, in agriculture, or in remote cabins or sheds, the standard guidance applies: ventilate before cleaning, dampen surfaces before sweeping to suppress dust, wear gloves and N95-rated masks when cleaning out rodent-affected spaces, and seal entry points to keep rodents out.

For people who have been in close contact with a confirmed case, public health authorities will reach out directly. Self-isolation for the duration of the incubation period is the standard precaution.

Where this stands historically

The MV Hondius outbreak is the largest documented person-to-person Andes virus cluster in over a decade. Earlier clusters, mainly in southern Argentina, involved a few cases each and were contained through contact tracing and isolation. The cruise ship setting — closed environment, international passenger list, weeks at sea — created an unusual transmission pattern that public health agencies are now studying closely.