Hondius hantavirus outbreak: two Science studies find person-to-person spread after rodent introduction

Two studies in Science

Two international studies published on 12 November 2026 in the journal Science reconstruct the Andes hantavirus outbreak aboard the cruise ship MV Hondius. The work combines the tracing of contacts and movements of those affected with analysis of the virus genome. The Icahn School of Medicine at Mount Sinai in New York coordinated the effort, with support from the World Health Organization and laboratories in France, Switzerland, the Netherlands, Spain, Canada, Senegal and South Africa. The University of Geneva said Swiss experts, including researchers from the Geneva University Hospitals, took part in the study.

Timeline on board

The Hondius left Ushuaia, Argentina, on 1 April 2026 with 149 people of 23 nationalities aboard, bound for the Canary Islands. The first case showed symptoms on 3 April, two days after departure. The outbreak was declared on 11 April, after which the ship docked in Tenerife and passengers and crew were repatriated to their countries for precautionary quarantine. The thirteenth case showed symptoms on 31 May, 60 days after the ship left Argentina. By 24 June, 13 cases and three deaths had been confirmed.

Tracing the transmission

The epidemiological work reconstructed the order of infections, and the timing carried weight. The University of Geneva said the gap of 60 days clearly exceeds the six-week maximum incubation period known for infection from rodents. The genetic analysis covered 10 of the 13 cases, and for those patients the viral genome showed a very similar imprint from one person to the next. That pattern confirmed transmission between humans on board. The study concludes that the virus entered the ship from a rodent and then spread between people, with crew members infected while caring for sick passengers.

“The sequence of symptom onset, the genomic data and the close contact patterns point to an introduction of the virus from a rodent to a passenger”

The virus is genetically close to natural Andes virus strains circulating in Patagonia, according to the University of Geneva. That finding rules out an artificial or modified pathogen, a claim that had circulated as rumour. Andes hantavirus stands apart from other hantavirus strains because it can pass between people, whereas the others usually spread when people breathe in dust contaminated by the droppings and secretions of wild rodents.

Open questions

The studies do not establish where or how the first infection occurred. El Confidencial reports that the source of the initial infection remains unknown, while the Patagonian lineage identified in the northern part of Argentina is the closest known relative. Le Temps reports that the work does not reveal the geographic origin of the outbreak. The Geneva team says the transmission chain and its starting point still contain unresolved gaps, which the study does not fill.