MV Hondius · Andes Orthohantavirus: Debrief
MV Hondius · Andes Orthohantavirus
Version 5. Status as of 25 June 2026. The 45-day monitoring window has closed. Thirteen cases, three deaths, one outstanding origin question. The ship is back in service. The answer is not yet in.
MV Hondius, a Dutch-flagged expedition vessel, departed Ushuaia, Argentina on 1 April 2026 carrying passengers and crew from 23 countries. Several weeks into the voyage, passengers began presenting with severe respiratory illness. Three died before the ship reached port. WHO was notified on 2 May. The ship docked in Praia, Cape Verde, on 3 May, was refused permission to disembark there, and subsequently received Spanish authorisation to proceed to Tenerife, arriving 10 May with 147 people aboard.
South African health authorities confirmed Andes orthohantavirus on 6 May.
As of 15 May, former passengers were hospitalised or in quarantine across 13 countries: Australia, Canada, France, Germany, the Netherlands, Saint Helena, Singapore, South Africa, Spain, Switzerland, Turkey, the United States, and the United Kingdom dependency of Tristan da Cunha. British military personnel parachuted to Tristan da Cunha on 10 May to reach a suspected case on the island.
Between the third WHO Disease Outbreak News report on 8 May and the fourth on 27 May, three additional confirmed cases were identified. A passenger from France became symptomatic during repatriation. A passenger from Spain tested positive on arrival after being asymptomatic. A Canadian case developed symptoms during contact follow-up. Two further cases from the Netherlands and Spain were identified through routine weekly testing of high-risk contacts.
An inconclusive case from the United States, where one of two laboratory results had returned positive, was subsequently determined negative on repeat testing and removed from the total count on 15 May. The CDC, working with state and federal partners, monitored 18 Americans with potential exposure. All completed their 42-day monitoring period on 21 June without developing disease. No hantavirus cases occurred in the United States as a result of this outbreak.
The inconclusive US case was not a miss. The system worked. Repeat testing ruled it out. The number held at thirteen.
MV Hondius arrived in Rotterdam on 18 May. The body of a deceased passenger was removed for cremation. The 23 remaining crew from four countries entered quarantine in the Netherlands. The vessel began disinfection in preparation for returning to service. By 18 June, RIVM confirmed that almost all passengers and crew had completed the 42-day quarantine period, having tested negative on exit. One person remained in quarantine briefly longer, having been in close contact with a hospitalised case. That person was subsequently cleared. The monitoring window is closed.
The working hypothesis, confirmed across WHO Disease Outbreak News updates through 27 May, is that the index case acquired the infection on land before boarding. Subsequent transmission occurred between people on the ship. The Andes virus is the only known hantavirus with documented human-to-human transmission, typically requiring close and sustained contact.
Chile has been ruled out. The time between the index case's visit to Chile and the onset of symptoms exceeds the maximum incubation period for ANDV, which runs to 42 days. The investigation is ongoing in collaboration with Argentine authorities, who assisted in reconstructing the travel itinerary of the first two cases in the Southern Cone. The Argentine National Hantavirus Epidemiological Circular was shared with the WHO response network. A precise geographic source has not yet been identified.
The European Commission, reviewing the latest sequence data, noted that results "strongly suggest the cases stem from the same very recent zoonotic spillover event." There is currently no indication of increased transmissibility or infection severity compared to other Andes virus strains. Novel variant characteristics have not been identified. The genomic record at this stage points to a single introduction, not a pattern.
The primary sequence record remains ANDV/Switzerland/Hu-3337/2026, the Swiss full-genome deposition at virological.org thread 1023, with all three genome segments complete (S, M, L). The Pathoplexus five-sequence set at thread 1029 constitutes the secondary record, with single-origin confirmation across all analysed samples. The community Nextstrain build at nextstrain.org/community/KU-MV/Hantavirus, maintained by the University of Bonn, remains live and monitored. No new sequences have been deposited as of this update.
A primer on Andes hantavirus published in npj Viruses in June 2026 cited the Hondius cluster as the most recent high-profile example of suspected human-to-human transmission, noting epidemiological parallels with previous Southern Cone outbreak investigations where super-spreader individuals with high viral loads drove onward transmission. The paper does not conclude the Hondius cluster fits that profile specifically, but the framing is notable as the academic community begins formal assessment.
The quarantine window is closed. The final case count is 13. The risk to the general population is, by the consistent assessment of WHO, ECDC and RIVM, very low. The response, for all the difficulty of managing an outbreak across a vessel in international waters with passengers from 23 countries, held. Exit testing was universal. All contacts came back negative. Nobody contracted Andes orthohantavirus from someone who had been on the ship, beyond the ship itself.
What this cluster does not close is the origin. Argentina remains under active investigation. The Andes virus is endemic across the Southern Cone, primarily in rodent populations in Patagonia, but human spillover events are rare, particularly on this scale. The precise exposure, the specific animal, the specific location, has not been confirmed. That question matters beyond the Hondius because the next expedition ship will also leave from Ushuaia, and the one after that.
The public sequence record should be watched. If an origin-linked sequence surfaces through Argentine national surveillance, the Nextstrain phylogeny will show it. The Hondius build at nextstrain.org/community/KU-MV/Hantavirus stays monitored for any new deposition. So far there is nothing. That may mean the answer is not yet in the data. It may mean the data has not yet been generated. The distinction matters and cannot currently be resolved.