A Rodent Virus With a Deadly Exception
Most hantaviruses quietly circulate in rodents, rarely crossing into humans and almost never jumping between people. Andes virus is the striking exception. It is the only known hantavirus that reliably spreads from human to human, and when it does, the results can be devastating.
From Silent Mice to Severe Lung Failure
In rodents, hantavirus infections are usually symptomless and lifelong. The animals shed virus in their urine, feces, saliva and even from their skin and fur, contaminating their surroundings. Other rodents can become infected by breathing in tiny droplets, eating tainted food, or coming into contact with these secretions.
When Andes virus reaches humans, the story changes dramatically. Instead of a silent infection, it typically causes hantavirus pulmonary syndrome, a brutal disease that strikes the lungs and heart. Patients can deteriorate quickly, and outbreaks of Andes virus are associated with case fatality rates between 20% and 40%—meaning up to two in five infected people may die.
A Virus That Breaks the Rules
Unlike its hantavirus cousins, Andes virus doesn’t stop at animal-to-human transmission. Past outbreaks have shown that it can jump from one person to another—but only under very specific conditions. Transmission has been documented in situations of close, sustained contact: household exposure, caregiving without protective equipment, or spending prolonged periods in crowded, poorly ventilated spaces.
How exactly the virus moves between people is still not fully understood. Scientists suspect airborne transmission plays a role—virus-laden particles carried in the air from one person’s secretions to another’s lungs—but the precise mechanisms remain unclear. What is clear is that brief, casual encounters seem far less risky than prolonged, intimate contact.
A Rare Threat With Global Resonance
The MV Hondius outbreak underscored both the danger and the limits of Andes virus. On board a confined ship, with shared spaces and close quarters, human-to-human spread appears to have helped drive the cluster of cases. Yet the World Health Organization judged the broader epidemic risk to be low, pointing out that previous Andes virus outbreaks have stayed largely confined to those close-contact settings.
The virus itself also carries a geographic fingerprint. It is normally found in the Andes mountains of Argentina and Chile, associated with a specific subspecies of long‑tailed mouse. No human cases had ever been recorded in Ushuaia or Tierra del Fuego, 1,500 kilometers south of the rodent’s known range—one of several clues suggesting a single, earlier infection event before passengers ever boarded the ship.
The Takeaway
Andes virus is a reminder that not all zoonotic diseases play by the same rules. A pathogen that is usually pinned to one rodent species in one mountainous region can, under the right conditions, leap into humans, spread between them, and ride modern travel networks across the globe—without ever becoming truly pandemic. Its rarity is reassuring, but its behavior is a warning of what’s possible when animal viruses find new ways to move through us.