What is hantavirus and how does it spread? The Andes strain and the Hondius outbreak explained

Hantaviruses are a group of RNA viruses in the Bunyaviridae family. About 30 subtypes have been identified, found globally in rodents — mice, voles, and some hamster species. The name comes from a 1976 identification near the Hantan River in North Korea among US military personnel.

The MV Hondius outbreak has put hantavirus back in public attention, because the Andes strain — endemic to Chile's Patagonia region — is the only hantavirus with documented human-to-human transmission. The Sin Nombre strain that causes 30-40 cases a year on average in the United States, and other North American types, only spread from rodents to humans. Andes's human-to-human capacity was first documented in a 1996 outbreak in Argentina's Bariloche region.

Rodent-to-human transmission occurs primarily through inhalation of contaminated particles in urine, droppings, or saliva. Hantavirus establishes a lifelong persistent infection in rodents — the rodent itself does not become ill but continues to shed the virus. Humans inhale aerosolised material from these substances or touch contaminated surfaces and then transfer it to mouth or nose. The risk is higher in enclosed, poorly ventilated environments — cabins, sheds, barns.

For Andes hantavirus, human-to-human transmission has been observed through: prolonged close contact involving the saliva of an infected person, body-fluid sharing, or living for days with an infected person in the same enclosed space. Household contact — same bed, same bathroom — was decisive in the Bariloche outbreak. The Hondius contact map suggests a similar pattern.

Clinical course: incubation is 14-21 days. The early symptom phase begins with flu-like symptoms — fever, muscle aches, weakness, headache, nausea. This phase lasts 3-7 days and is typically mild. About 30-50 per cent of cases then enter a second phase: hantavirus pulmonary syndrome (HPS), a severe respiratory failure. Capillary permeability in the lungs breaks down, fluid accumulates, and the patient deteriorates quickly.

Professor David Anderson of the London School of Hygiene & Tropical Medicine told the BBC: "The pathophysiology of this disease is different from any other respiratory virus — the virus directly targets pulmonary capillaries. Treatment is supportive only: high-flow oxygen, mechanical ventilation if needed, sometimes extracorporeal membrane oxygenation. There is no specific antiviral; trials with ribavirin have not produced conclusive results."

Mortality reaches 35-50 per cent of confirmed HPS cases. This is far higher than COVID's peak (about 5 per cent in the worst waves). But infectiousness is much lower, which is why hantavirus does not have global pandemic potential. Andes outbreaks remain rare: 20 cases in the 1996 Bariloche outbreak, 36 cases in a 2018-2019 Patagonia outbreak, and 11 confirmed cases on the Hondius so far.

A further notable feature: hantavirus antibody production is robust. Recovered patients carry long-lived — likely lifelong — IgG antibodies that confer protection. This is a critical fact for vaccine development. Two Phase 1 vaccine trials are currently underway worldwide for the Andes and Sin Nombre strains; both are on mRNA platforms. Vaccine development is accelerating because of post-outbreak funding pressures.

In the Hondius outbreak, virus sequencing was performed at the Chilean Ministry of Health laboratory. The genome showed 99.7 per cent overlap with the strain documented in Patagonian Oligoryzomys longicaudatus rodents. That supports the hypothesis that the outbreak began through a rodent cave tour during the ship's stop at Punta Arenas. Initial patient symptoms began 17 days after that visit.

General public guidance is straightforward: when working in cabins, sheds or agricultural settings with high rodent populations, use gloves and masks; clean surfaces contaminated with rodent urine or droppings with a 1 per cent sodium hypochlorite solution rather than dry sweeping (which generates aerosols); and during travel, take rodent-contact tours only in environments known to be safely managed. For everyday life, the risk of Andes hantavirus transmission to the general public is negligible.