Published on
An international consortium including UNIGE and HUG has clarified the origin and mode of transmission of the Andes virus, which spread aboard a cruise ship in spring 2026.
An international collaboration involving the University of Geneva (UNIGE) and the Geneva University Hospitals (HUG) has confirmed that the hantavirus outbreak aboard the M/V Hondius in April 2026 stemmed from an initial infection acquired on land, followed by person-to-person transmission on board. Genetic analyses show that the virus belongs to a natural lineage of the Andes virus circulating in Argentine Patagonia. Published in Science, these findings highlights the vital role of scientific cooperation in responding to global health emergencies.
In April 2026, an outbreak of severe respiratory infections, presenting as hantavirus pulmonary syndrome (HPS), was detected aboard the cruise ship M/V Hondius, which had left Ushuaia, Argentina, on 1 April. Analyses conducted by the UNIGE/HUG Geneva Centre for Emerging Viral Diseases, a WHO Collaborating Centre, identified the virus as belonging to the Andes strain. In total, thirteen passengers were affected, three of whom died.
Two questions remained unanswered: how did the virus spread on board, and where did the infection originate? "Hantaviruses are usually transmitted by inhaling dust contaminated with the secretions of wild rodents. The Andes virus, however, has the rare ability to also pass directly from person to person through close, prolonged contact," explains Isabella Eckerle, Director of the UNIGE/HUG Centre, which also hosts the Swiss Federal Office of Public Health (FOPH) reference lab for emerging viral diseases.
This extraordinary international effort underlines how essential it is to invest in national capacities and international scientific networks before a crisis occurs.
Tracing the virus's path
To gain further insights, an international collaboration in which Isabella Eckerle is actively involved carried out an epidemiological and genetic investigation. The scientists initially observed that the first case was reported on 3 April, shortly after departure from Ushuaia. By contrast, case "13" developed symptoms on 31 May 2026, 60 days after leaving Argentina. This far exceeds the maximum known incubation period for initial infection from rodents, estimated at six weeks. This part of the research further documented close and prolonged contact between this patient and another confirmed case, case "10".
The team then sequenced the virus genome, determining the order of the elements that make up its genetic material, in ten of the thirteen affected individuals. They found that the genetic material was highly similar across all individuals. "The sequence of symptom onset, the genomic data, and the patterns of close contact all point to an initial introduction of the virus from a rodent to a passenger, followed by secondary person-to-person transmission on board the ship," says Isabella Eckerle, citing the study's conclusions.
A known virus
The analysis also shows that virus from the cruise ship is genetically very close to natural strains of the Andes virus circulating in Argentine Patagonia. This rules out rumours of an artificial or reassorted virus, or one that had undergone abnormal mutations. The international consortium also published a second article in Science, tracing the historical lineage of the virus strain in Patagonia.
This work is the result of extensive international collaboration, particularly through the independent comparison of results between laboratories in several countries (France, Switzerland, the Netherlands, Spain, Canada, Senegal, and South Africa). This strengthened the robustness and reliability of the genomic analyses used to trace the transmission pathway on board. "This extraordinary international effort shows what we can achieve by working together, across institutions and borders. It underlines how essential it is to invest in national capacities and international scientific networks before a crisis occurs," concludes Isabella Eckerle.
