The origin of the MV Hondius Andes outbreak

In April-July 2026, Andes virus (ANDV) caused an outbreak aboard the MV Hondius cruise ship resulting in 12 confirmed cases and three deaths. Before symptom onset, the index case had travelled through hantavirus-endemic regions of Chile and Argentina, leaving the geographic origin of infection unresolved. We conducted phylogenetic and phylogeographic analyses using newly generated ANDV genomes from human cases and rodent reservoirs to investigate the likely origin of the outbreak. Through phylogenetic analyses, we show that the outbreak genome falls within a geographically structured lineage spanning southern Chile and Argentine Andean Patagonia. Using phylogeographic reconstructions across all three segments, integrated with the index case's travel itinerary, we identified the Toltén-Lanco area of southern Chile as the most likely geographic origin of the outbreak genome, with two candidate locations accounting for >98% of the posterior support. However, the index case visited this area 62-66 days before symptom onset, exceeding the conventionally reported ANDV incubation period of 7-42 days. Thus, while genomic evidence supports a southern Chilean origin of the outbreak genome, the timing and circumstances of transmission to the index case remain unresolved.