Hantavirus: Of mice, men and cruise ships

Cruise ships are small self-contained floating cities, capable of transporting thousands of passengers across oceans, but they also present a closed community setting with an underappreciated infectious disease threat. 

While norovirus, together with influenza, COVID-19, respiratory syncytial virus and other respiratory viruses are commonly associated with outbreaks on cruise ships, the recent reports of zoonotic hantavirus infection linked to a cruise voyage in the Atlantic have focused attention to the possibility that rodents can introduce dangerous zoonotic pathogens into crowded shipboard environments, transforming a localised zoonosis into an international event. Moreover, many passengers are older adults and/or may have underlying health conditions, which put them at risk of complications from viral infections. As cruise ships may carry infected individuals for weeks across oceans, they can become infected before docking at several ports. When symptoms emerge, surveillance, laboratory testing and containment efforts can be delayed.

Hantaviruses on the MV Hondius Cruise ship

A cluster eight of cases of severe respiratory illness was reported to the World Health Organization (WHO) on May 2, 2026 and confirmed to be caused by a particular hantavirus known as Andes Virus. By May 13, there were nine laboratory confirmed cases and two probable cases, and 3 persons died. By May 27, there were 13 cases including the 3 deaths.

The Andes Virus is one of the few hantaviruses capable of limited person-to-person transmission but WHO assessed the risk of further epidemics or a pandemic from this event to be low with the risk for passengers and crew on the ship being moderate. The ship left South America, on April 1, but after 10 days, a 70-year-old Dutch passenger died on board. Two weeks after that, his widow died in South Africa. On May 2 the Andes hantavirus was confirmed by reverse transcription polymerase chain reaction (RT-PCR). Around the world, dozens of contacts have been forced to quarantine for up to 42 days. 

How did the virus enter the ship? 

The exact origin remains uncertain. It is possible that an already zoonotically infected passenger transmitted the virus to others or that the virus was spread to passengers via rodents on the ship. Hantaviruses are typically zoonotic viruses transmitted through inhalation of aerosolized rodent urine, saliva, or faeces, particularly from infected mice and rats. The Andes virus strain, confirmed in this outbreak, is unusual because limited person-to-person transmission has previously been documented in South America. 

Throughout history, rodents have accompanied ships. Rats and mice were central to the spread of plague through infected fleas in the 1300s and while modern cruise ships maintain strict sanitation systems, rodents still occasionally infest food storage areas, cargo compartments, wharfs and waste-handling facilities. Thus, maritime environments provide an ecological niche for the potential emergence of rodent-associated microorganisms.

Clinical Features

Hantavirus infections in humans present as two distinct, severe, and potentially fatal syndromes; Hantavirus Pulmonary Syndrome (HPS) dominating in the Americas and Haemorrhagic Fever with Renal Syndrome (HFRS) dominating in Europe and Asia.

The incubation period for hantavirus infections ranges from 1-8 weeks with early symptoms resembling an influenza-like illness, and can include abdominal pain, nausea and vomiting. 

Blood tests commonly show abnormal liver enzyme concentrations, elevated lactate dehydrogenase, thrombocytopenia, leucocytosis and haemoconcentration. Chest x-rays often demonstrate bilateral interstitial infiltrates progressing to diffuse pulmonary oedema.

Diagnosis requires a high index of suspicion, especially if there is a history of rodent exposure, travel to endemic areas, or exposure to rodent-contaminated environments. Available diagnostic tests for Hantavirus include serologic testing for hantavirus-specific IgM and IgG antibodies, RT-PCR and immunohistochemistry. It should be noted that early testing may be negative, and if clinical suspicion remains high, further testing is warranted every few days. 

Hantaviruses infect endothelial cells lining blood vessels and pathology results from immune-mediated vascular dysfunction more than direct cytopathic cellular destruction. Increased capillary permeability leads to plasma leakage, hypotension, petechiae pulmonary oedema, and organ dysfunction. 

In HPS, infection primarily affects the pulmonary microvasculature. Cytokine activation and immune dysregulation cause rapid fluid accumulation in the lungs. As HPS progresses, patients develop cough, dyspnoea, tachypnoea, and chest tightness. Patients can deteriorate dramatically to respiratory failure within hours once pulmonary symptoms begin. 

In HFRS, the kidneys become major targets of vascular leakage and inflammation. Early symptoms can include; low blood pressure, intense headaches, back and abdominal pain, fever, chills, nausea, and blurred vision. This may be followed by vascular leakage, acute kidney injury, thrombocytopenia, and haemorrhagic manifestations may then develop. Severe cases can progress to circulatory collapse and death. Disease severity varies and depends on the specific hantavirus causing the disease.

Treatment

There is no specific treatment for hantavirus infection. Early medical intervention is crucial, often requiring oxygen therapy, haemodynamic support and mechanical ventilation in intensive care. HPS patients may need intubation. For HFRS, patients may need dialysis to remove toxins from the bloodstream. Ribavirin and favipiravir have shown some benefit in selected HFRS cases but evidence for HPS cases remains limited. 

Recombinant, subunit, DNA, inactivated, virus-like particle and virus-vector vaccines have all been previously studied in a variety of animal models and work has also been initiated on mRNA vaccines, but a registered vaccine is not expected for many years. However, in China and the Republic of Korea, a whole virus inactivated vaccine against Hantaan or Seoul virus are licensed for human use, but the protective efficacies of these vaccines are uncertain. 

Hantavirus transmission

Hantaviruses are maintained in nature by chronically infected rodents and some small mammals, which shed the virus in urine, faeces and saliva. Human infections generally occur after inhalation of aerosolized particles contaminated with rodent excreta but also through cleaning or disturbing nesting materials. More rarely, hantaviruses can be contracted by eating food contaminated with mouse fluids, being bitten or scratched by an infected rodent, and touching contaminated environments or surfaces. 

Hantavirus infections from human-to-human spread are rare as is asymptomatic infection. Humans are usually ‘dead-end hosts’ with the exception of the Andes virus (which affected the MV Hondius cruise ship, but fortunately there was very limited person-to-person transmission). However, there are about 200 000 human cases of hantavirus infections reported annually. In 2018/2019, an efficient ‘super-spreader’ birthday party event was reported in Argentina involving Andes virus, resulting in 11 deaths of 34 confirmed infections. The relationship between the Andes virus on the cruise ship and other circulating Andes viruses remains to be determined especially in relation to mutations possibly causing increased transmissibility.

Prevention of hantavirus transmission in household or closed community settings depends on controlling rodent infestations and disinfecting contaminated areas with bleach rather than sweeping or vacuuming, which can aerosolise the virus and be inhaled by humans. 

Australia is the only continent where no confirmed human cases of hantavirus infection have been recorded; however, antibodies to hantavirus have been detected in some Australian rodents. 

Public Health Implications

Cruise ships present unique infection-control challenges as they combine many services within confined spaces over potentially long periods. Outbreak investigations require rapid coordination between maritime authorities, public health agencies, laboratories, the WHO and other international health organisations. 

Rodent control remains the cornerstone of prevention. Effective measures include; rapid remediation and reporting of infestations, rigorous food storage practices, strict controls on waste management, structural exclusion of rodents, regular sanitation inspections, monitoring of cargo-loading areas, and regular environmental cleaning to safely remove dried rodent excreta. Passenger education is also critical especially for onshore expeditions to endemic regions, rural settings, or wildlife exposure. 

Risk Assessment

The likelihood of acquiring hantavirus while on a cruise ship is extremely low as hantaviruses do not spread efficiently through casual social contact. However, there are public health challenges for viruses that combine low incidence with high case fatality rates. Cruise ship medicine therefore requires preparedness even for rare pathogens.

Conclusion

In maritime settings rodent-borne viruses remain an uncommon infectious threat. The detection of Hantaviruses, particularly Andes virus, have highlighted the vulnerability of cruise ships to emerging zoonotic diseases more generally. Although overall risk to passengers is low, the severity of hantavirus infections and other emerging zoonotic diseases demands vigilance.

Professor Gary Grohmann is a Board member and a member of the Scientific Advisory Committee of the Immunisation coalition. He is a former Director of Immunobiology at the Therapeutic Goods Administration and currently works as an independent consultant.

Professor Robert Booy is an infectious diseases paediatrician. He is a Senior Professorial Fellow at the University of Sydney Children’s Hospital Westmead Clinical School and a member of the Scientific Advisory Committee of the Immunisation Coalition.

Acknowledgement: Gratitude to Dr John McEwen for reviewing the manuscript.