Dr Benjamin Brennan, Group Leader and Senior Lecturer, MRC-University of Glasgow Centre for Virus Research, University of Glasgow, said:
Do we know for sure yet (re transmission) or do we need to know more and wait for the results of investigations to be sure where the cases became infected?
“The WHO’s working hypothesis of mixed transmission pathways (rodent exposure in endemic areas, plus limited person-to-person spread among close contacts) aligns with what we’d expect from Andes virus in this setting, but confirmation awaits full epidemiological and laboratory investigation. The ship’s itinerary visiting multiple islands with wildlife exposure creates several plausible exposure windows, so determining whether each case picked up the infection from rodents or from close contacts requires careful case-by-case analysis of timelines and exposures. This remains work in progress. Therefore, we should hold fire on firm conclusions/statements until the data clarifies what actually happened.”
Dr César López-Camacho, Jenner Investigator and Head of the mRNA Technology Programme at the Jenner Institute, University of Oxford, said:
“This cluster is important because the meaning of the outbreak depends heavily on viral identity. For most hantaviruses, a small group of cases would usually point first to a shared environmental exposure. But if the virus involved is Andes virus, which WHO now considers likely, the interpretation becomes more complex because Andes virus is the principal hantavirus associated with documented person-to-person transmission. The scientific priority is therefore not only case confirmation, but rapid lineage resolution and careful reconstruction of exposure histories. Events like this remind us that the challenge is not just detecting unusual infections, but linking diagnostics, sequencing and epidemiology quickly enough to understand what kind of outbreak we are dealing with.”
Dr Giulia Gallo, Postdoctoral Scientist in the Viral Glycoproteins Group, The Pirbright Institute, said:
What does the latest info from the WHO suggest – are there still uncertainties and more things we need to know?
“At the moment, seven cases have been reported, two have been confirmed with hantavirus infection and five remain suspected. Further analysis is being performed to confirm the hantaviral species causing the outbreak. The open question remains on how these patients came into contact with the virus in the first place. Two patients visited South America before boarding the ship, which could represent a way of infection. The journeys of the other patients, and therefore potential exposure to the virus, still needs to be elucidate for the other cases. Epidemiological investigations are being carried out on the ship, to assess how people could have encountered the virus. This still remains to be clarified.
Is it significant that the WHO info says “Cases 1 and 2, had travelled in South America, including Argentina, before they boarded the cruise ship on 1 April 2026”?
“This information could guide to the identification of the potential pathogen. Andes virus is found in this part of South America, and the symptomatology presented by the patients aligns with what is known about the Andes virus infection in humans. This could inform on countermeasures that could be undertaken and inform rapid response for exposed people.
How worrying is this – what is the risk to those on the ship and to members of the public in the relevant locations?
“The WHO currently assesses the risk of infection to the global population as low. Measures on the ship have been taken (maximal physical distancing, isolation, evacuation of infected patients) to reduce the additional exposure to the virus. Monitoring is fundamental for the passengers and crew on the ship, to rapidly react to any development. In parallel, further investigations such as serology and sequencing of patients, is going to help determine the severity of the outbreak and guide solutions to protect people on board.”
Dr Charlotte Hammer, Assistant Professor and infectious disease epidemiologist, University of Cambridge, said:
“Outbreak investigations will be ongoing at the moment to establish the exposure of the cases. Hantavirus is present in Argentina and other parts of South America and has an incubation period of up to eight weeks. Therefore, it is quite possible and even likely that the cases have been exposed during their time in South America. There is a (albeit small) risk of Hantavirus infection across South America, just like there is a small risk of Old World Hantavirus infections in Europe whenever one is in a context where exposure to rodent droppings is likely for example when cleaning garages or garden sheds. Further details on the exposure location and method are necessary to fully assess the risk to others but the risk to the general public is very small. The risk to those on the ship is somewhat higher as there is a higher potential for shared exposure or transmission either though human-to-human transmission which is rare but possible, or through a shared exposure either onboard the ship or during land activities.”
Prof Mark Fielder, Professor in Medical Microbiology, Kingston University London, said:
“The cases of Hantavirus detailed by the WHO indicate that a total of seven cases have been identified as of the 4th May 2026, that comprises two laboratory confirmed cases and a further five suspected cases. Of the cases reported one patient is critically ill, three patients report mild symptoms, and three patients have lost their lives. The latest statement from the WHO is a case definition defining the patients involved in the outbreak and detailing the pattern of the disease development and progression. It is noted that the vessel and its passengers have undertaken multiple stops in ecologically diverse and remote locations, although the level of patient contact with any wildlife during the trip is as yet undetermined. This is important as Hantavirus can be transmitted to humans via contact with the urine, faeces and/or saliva of infected rodents. It is also known that Hantavirus causes relatively small numbers of cases annually in places such as Argentina, Paraguay, Brazil and Chile with only hundreds of cases reported. However, despite this low number of cases the case fatality rate can be between 20%- 40% meaning it is a public health concern. The infection can become evident in a patient between one to eight weeks after exposure.
“Whilst this information is of concern for the patients that have contracted the infection it should be noted that human to human infection is rare and is largely associated with prolonged and close contact between people in the same household or those with intimate contact. This sort of transmission has been documented for the Andes virus in the Americas.
“With the current understanding of the ongoing infection and the likelihood that stringent infection control measures are being implemented on board the vessel, it is likely that further ongoing transmission will be limited. The isolation of infected patients, regular handwashing, monitoring of close contacts, and the application of infection control measures will all be critical to limiting and halting onward spread of the disease.
“Once the ship docks it is likely that arrangements will be made for the remaining passengers and crew to be medically assessed and then be taken into a period of quarantine and monitoring to ensure the control of any infection and provide early medical intervention where needed.”
Dr Benjamin Brennan, Group Leader and Senior Lecturer, MRC-University of Glasgow Centre for Virus Research, University of Glasgow, said:
What does the latest WHO info suggest – are there still uncertainties?
“The WHO has identified seven cases including two laboratory-confirmed hantavirus infections and five suspected cases, with illness onset between 6 and 28 April.
“Key uncertainties remain: the precise source of infection aboard ship hasn’t been pinpointed (hantavirus typically spreads through rodent contact, so its appearance in a cruise ship environment raises questions about contamination pathways), and the full extent of person-to-person transmission remains unclear. Only limited human-to-human spread has been documented previously with Andes virus. The incubation period and disease progression rates on this outbreak warrant careful monitoring.
Why is the South America travel history significant?
“Cases 1 and 2 travelled in South America, including Argentina, before boarding the cruise ship. This is a crucial piece of epidemiological information in that it suggests the infection was acquired in a hantavirus-endemic region and brought aboard, rather than originating from shipboard conditions. Argentina is where Andes virus circulates, so identifying which virus strain is responsible is essential for assessing the ongoing risks associated with the outbreak.
“The travel histories of other passengers and crew members are still being investigated, so it remains uncertain whether additional individuals may have had exposure to hantavirus sources in endemic areas before boarding or during port stops. However, most passengers and crew will have been in close quarters throughout the virus incubation period, leading to the potential for secondary cases to occur.
How worrying is this?
“WHO currently assesses the risk to the global population from this event as low, and there’s no evidence of spread beyond the ship and those who had direct contact with cases. However, the situation remains serious for those aboard and their contacts, seven cases have been identified with three deaths, one critically ill patient and three mild cases. The real concern is whether additional cases emerge among the remaining 140+ passengers and crew during this critical window. Currently, rapid isolation, medical evacuation and contact tracing should be appropriately prioritized, to get the affected patients the full and comprehensive medical treatment they require.”
Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:
“We now know that two of these cases known to have travelled in South America prior to boarding the vessel. This does indicate that those cases were likely infected by an environmental exposure at that point. The incubation period from initial infection to symptoms can be several weeks, so it does fit within the timelines presented.
“We do not yet know about the movements of cases 3 and 4 prior to boarding the ship. We also do not yet know if this is the Andes strain of hantavirus, with laboratory tests ongoing. There have been documented cases of human-to-human transmission from the Andes strain, specifically within Argentina. In one outbreak, there was a single environmental exposure to rodents and three symptomatic patients then infected others at crowded social events, resulting in 34 cases and 11 deaths.
“Here, on the MV Hondius, we do not yet know if there is human-to-human transmission. Knowledge of the strain is therefore important to understanding the risks to the passengers who are still on board.”
Ref, Andes strain of hantavirus and transmission - https://www.nejm.org/doi/full/10.1056/NEJMoa2009040
Declared interests
Dr César López-Camacho: “I declare no conflict of interest.”
Prof Mark Fielder: “No conflicts of interest to declare.”
Prof Roger Hewson: “I am Professor of Virology at the London School of Hygiene & Tropical Medicine and am also employed part-time by the UK Health Security Agency. These comments are made in my academic capacity at LSHTM and do not represent an official UKHSA statement. UKHSA media enquiries should be directed to ukhsa-pressoffice@ukhsa.gov.uk.”
Dr Giulia Gallo: “I have no conflict of interest.”
Dr Toshana Foster: “I declare that I do not have any conflicting interests.”
Prof Sir Andrew Pollard: “Nothing I can think of for hanta.”
Prof Jon Cohen: “I have no conflicts to declare.”
Dr Benjamin Brennan: “No COIs to declare.”
Dr Liam Brierley: “I disclose previous funding for work unrelated to hantaviruses from CSL Seqirus Ltd.”
Dr Charlotte Hammer: “I have no interests to declare.”
Prof Paul Hunter: “No COIs.”
Dr Michael Head: “No COI to declare.” | 
