Hantavirus on a Cruise Ship: Understanding the Atlantic Outbreak

This week has brought some unexpected news to the infectious disease community. The WHO issued a Disease Outbreak News notification on 4 May 2026 about a hantavirus cluster aboard the MV Hondius. Not many people have heard of this disease, but the setting is unusual. The implications, depending on what investigations reveal, may be significant.

Here is an explainer on hantavirus disease, the current outbreak, and current options for treatment and prevention.

Hantavirus disease is caused by multiple hantaviruses; a family of RNA viruses carried by rodents (primarily rats, mice, and voles, depending on the species and the part of the world). Humans typically become infected by inhaling aerosolised particles from rodent urine, droppings, or saliva. The classic scenario involves disturbing dust in an enclosed space where rodents have been living, such as cleaning out a long-disused shed, or sleeping in a cabin with an unnoticed infestation.

Direct rodent bites can also transmit infection, but airborne exposure to contaminated dust is much more common. Crucially, person-to-person transmission is extremely rare. There is one important exception, which is the Andes virus. This particular virus is found in Chile and Argentina, and has been documented to occasionally pass between humans, particularly close household contacts.

Hantaviruses cause two distinct clinical syndromes, broadly mapping to geography:

Haemorrhagic fever with renal syndrome (HFRS) is caused mainly by Hantaan virus in Asia and Puumala virus in Europe and Scandinavia. The kidneys are the principal target, and the disease ranges from a mild flu-like illness to severe organ failure with bleeding.

Hantavirus pulmonary syndrome (HPS) is caused mainly by Sin Nombre virus in North America and Andes virus in South America. Here the lungs are most affected. The clinical course is characteristic: a few days of non-specific fever, muscle aches, and gastrointestinal symptoms, followed by rapid deterioration as the lungs fill with fluid. Acute respiratory distress syndrome and shock can develop within hours.

Hantavirus disease is extremely severe. Case fatality for HPS sits at 35–40%, even with modern intensive care. HFRS is generally less lethal but still kills 1–15% of those infected, depending on the species involved.

The good news is that Hantavirus infection is very rare. Fewer than 900 cases of HPS were recorded in the United States between the start of surveillance in 1993 and the end of 2023. It is the kind of disease most clinicians will never encounter in their careers.

The MV Hondius, a Dutch-flagged expedition cruise ship operated by Oceanwide Expeditions, departed Ushuaia in southern Argentina on 1 April 2026 across the South Atlantic. There were ~150 people on board in total.

Between 6 and 28 April, passengers began falling ill. According to the WHO, the clinical picture was striking: fever and gastrointestinal symptoms, followed by rapid progression to pneumonia, ARDS, and shock. These are the classic features of severe hantavirus pulmonary syndrome.

As of the WHO update on 4 May, there were two laboratory-confirmed cases and five suspected cases. Three patients had died, one was critically ill, and three had milder symptoms. Two of the early cases (a couple) had travelled in Argentina, including hantavirus-endemic regions, before boarding the ship. This might fit with the disease being caused by the Andes virus, but the specific Hantavirus is yet unknown.

Two plausible mechanisms are being considered. The first is that the ship became contaminated, perhaps by infected rodents at port, with passengers exposed via dust or surfaces. The second would be more concerning: human-to-human transmission of Andes virus, which would represent one of the largest such clusters ever documented.

What are the clinic implications?

• The global risk is low. The WHO has been clear on this point, and there is no case for travel restrictions or public alarm.

• The local risk to those on the ship is significant, particularly given the limitations on intensive care available at sea.

• Whether human-to-human transmission is occurring will be the key question to resolve.

The ship is currently anchored off Praia, the capital of Cape Verde, after being refused entry to port. Medical assessments have been organised for the sickest patients, contact tracing is underway (including for passengers on a Johannesburg-bound flight that one of the cases boarded before her death), and laboratory investigations are ongoing.

There is no specific antiviral therapy proven effective against hantavirus. Care is largely supportive: oxygen, mechanical ventilation, careful fluid management, and in the most severe cases, ECMO (heart-lung bypass) to take over for failing lungs. The key factor is access to a centre that can deliver this level of care quickly, which is why a cluster on a cruise ship in the middle of the ocean is such a concern.

As is true for all the viruses which cause deadly haemorrhagic fevers, what we really need is a vaccine. The picture here is more interesting.

Inactivated hantavirus vaccines have been used in South Korea and China for decades against HFRS, with mixed views on their effectiveness. In the West, no hantavirus vaccine is licensed. Several candidates are in early-phase development, including DNA vaccines targeting the Hantaan, Puumala, and Andes virus glycoproteins, with encouraging immunogenicity data from Phase 1 trials.

I have particular interest in this topic, as I am the Principal Investigator of an ongoing Phase 1 hantavirus vaccine clinical trial (ISRCTN17868912), which has now completed enrolment. The vaccine (MVA-Hanta) has been developed by the UKHSA using a backbone of Modified Vaccinia Ankara (MVA) - the virus which was used as the smallpox vaccine. The MVA virus has no relationship to hantaviruses itself, but it can be modified to encode for antigens which are found in other viruses (or bacteria).

Unfortunately this trial, and the other phase I trials, are still too early in the life cycle of development to provide clinical benefit towards outbreaks. Hopefully we are not too far off moving to phase II trials and being able to offer protection during rare outbreak scenarios.

Hantavirus disease is severe, and presents differently depending on which part of the world it occurs (due to different hantavirus disease causing viruses being implicated). In Europe/Asia is presents mostly as Haemorrhagic Fever with Renal Syndrome, and in South America as the more severe Hantavirus pulmonary syndrome. Treatment options remain limited and are mainly supportive. Vaccines are coming, but slowly.

A hantavirus outbreak on a cruise ship is highly unusual and concerning event. For the wider public, the risk remains very, very low. Hantavirus is not going to start spreading through the general population like COVID-19 or influenza. This is not the start of a new pandemic, and there is no reason for people outside of the ship to worry.

It remains to be seen whether the outbreak is deemed to be caused by the presence of hantavirus carrying rodents on-board the ship, or the more concerning possibility of human-to-human transmission (with involvement of the Andes virus). Hopefully further laboratory analysis and outbreak investigation will yield some more definitive answers.