Andes Orthohantavirus Outbreak Linked to Cruise Ship Travel

As of 18 June 2026, a total of 13 cases of Andes orthohantavirus (12 confirmed and one probable) have been reported. This outbreak has been linked to the Dutch-flagged expedition cruise ship MV Hondius. The case-fatality rate observed in this event was 23%.^1,2,3

The outbreak involved individuals from 23 nationalities, underscoring the international scope of the event. The public health response required medical evacuation, repatriation, coordinated international contact tracing, isolation, quarantine, and subsequent clinical and laboratory testing follow-up for affected individuals.^1,2,3

Epidemiology of the Outbreak

All reported cases to date have been either passengers or crew members of the MV Hondius. Specifically, 10 out of 121 passengers (8%) and 3 out of 61 crew members (5%) were affected.^1,2,3

Ongoing monitoring and investigations are being conducted to clarify the source of the outbreak, identify specific risk factors associated with transmission, and implement measures to prevent further spread of the virus.^1,2,3

The event highlights the complex challenges in global outbreak preparedness, particularly concerning zoonotic pathogens with potential for human-to-human transmission, such as Andes orthohantavirus. The interconnectedness of global travel, exemplified by expedition cruise ships, necessitates a comprehensive One Health approach to address emerging infectious threats effectively.²

In vitro studies have demonstrated potent antiviral activity of 4'-Fluorouridine against diverse orthohantaviruses, including Andes virus. This research may inform future therapeutic strategies for ANDV.³

Clinical Context of Andes Orthohantavirus

Andes orthohantavirus (ANDV) is a rodent-borne zoonotic pathogen primarily transmitted to humans through inhalation of aerosols contaminated with rodent excreta. Unlike other hantaviruses, ANDV is unique for its documented human-to-human transmission capability, which significantly increases its pandemic potential. The virus causes Hantavirus Cardiopulmonary Syndrome (HCPS), a severe and often fatal disease characterized by rapid onset of respiratory distress, pulmonary edema, and cardiogenic shock. The incubation period for ANDV typically ranges from 9 to 33 days, but can extend up to 45 days, complicating early detection and contact tracing efforts. Initial symptoms are non-specific and include fever, myalgia, headache, and gastrointestinal complaints, making clinical diagnosis challenging without a high index of suspicion, especially in non-endemic areas. Progression to severe respiratory failure can be rapid, often within hours of symptom onset.^1,2

Methodology of Outbreak Investigation

The investigation into the MV Hondius outbreak involved a multi-country collaborative effort. Public health agencies from various nations, including the United Kingdom Health Security Agency (UKHSA), coordinated the response. Initial case identification relied on clinical suspicion followed by laboratory confirmation using reverse transcription-polymerase chain reaction (RT-PCR) for ANDV RNA and serological assays for anti-ANDV IgM and IgG antibodies. Epidemiological investigations included detailed interviews with confirmed and probable cases to ascertain travel history, potential exposures, and contact networks. This data facilitated the identification of the MV Hondius as the common exposure point. Contact tracing extended to all passengers and crew members, irrespective of nationality, who were on board the vessel during the identified exposure period. Individuals identified as contacts underwent risk assessment, and those deemed high-risk were advised to undergo isolation or quarantine with active symptom monitoring and follow-up testing. Medical evacuations and repatriations were executed in close coordination with international health regulations and national public health protocols to ensure safe transport and continued care.¹

Patient Populations and Risk Factors

The affected population primarily comprised adults, consistent with typical cruise ship demographics. While specific age ranges and underlying comorbidities for the 13 cases have not been detailed, general risk factors for severe HCPS include advanced age and certain chronic conditions. The observed case-fatality rate of 23% aligns with the known severity of HCPS caused by ANDV. The distribution of cases between passengers (8%) and crew members (5%) suggests a relatively widespread exposure event on board the vessel, rather than a highly localized point source. Further investigation aims to elucidate specific activities or locations on the ship that may have contributed to transmission. The international diversity of the affected individuals (23 nationalities) underscores the global reach of modern travel and the potential for rapid international dissemination of infectious diseases.^1,2

Limitations of the Current Understanding

The ongoing nature of the investigation presents several limitations to a complete understanding of this outbreak. The precise source of the ANDV infection on the MV Hondius remains unclear. It is unknown whether the virus was introduced by an infected individual or through a contaminated environment on the ship, potentially via rodent vectors that may have boarded the vessel. The exact mechanism and extent of human-to-human transmission within the cruise ship environment also require further clarification. Retrospective contact tracing can be challenging due to the transient nature of cruise ship populations and potential recall bias among individuals. Furthermore, the full spectrum of mild or asymptomatic infections may be underestimated, as surveillance efforts often focus on symptomatic cases requiring medical attention. The long incubation period of ANDV also means that additional cases could emerge, necessitating continued vigilance and follow-up.^1,2