Epidemiological investigations are detective stories. There is a body (or bodies), the deaths are connected in some way, and there is a race to find out who did it, as well as to protect those who might be next, before the killer strikes again. The tale of the MV Hondius, a Dutch-flagged, ice-strengthened expedition ship travelling the Atlantic cruise route between Europe and the southern polar regions, is one such story. The Hondius left the southern Argentinian port of Ushuaia, the starting point for most Antarctic cruises, on April 1, for what was to be a 24-day return voyage to Europe. It carried around 160 passengers and crew from 23 countries. The return trip would cross the Atlantic, stopping at select ports along the way. Among the passengers was a Dutch couple in their sixties, avid bird-watchers who had traveled extensively in Chile and Argentina before boarding.The 69-year-old Dutch man was the first to die. He had initially complained of a fever, headache and diarrhoea. Breathing difficulties and acute respiratory distress followed abruptly before his death on April 11. His body was taken off the ship at St. Helena almost two weeks later to be repatriated, accompanied by his wife. Altogether, 24 passengers disembarked there, including a number of Americans. His wife fell ill shortly after leaving the ship, collapsing at an airport in Johannesburg and dying shortly thereafter in a local health facility.Meanwhile, on the ship, a British national began to experience breathing difficulties similar to those of the Dutch man and was evacuated to an intensive care unit (ICU) in South Africa. On May 2, a German woman died on board. She had been unwell for only 5 days. The same day, tests conducted in South Africa confirmed a specific viral infection in the British man and on May 4, the same infection was confirm in the case of the German woman.Whatever was sickening the patients did not respond to standard antibiotics carried by the high-end cruise ship’s doctor. The disease progressed similarly across patients, presenting initially like a flu. It was clearly infectious – the doctor who had treated the Dutch man and his wife was among those who fell ill early. Tests ultimately established that all those who died were infected by the same pathogen: a virus called the hantavirus, specifically the Andes strain. The virusThe hantavirus family is large, with around 28 members known to cause diseases in humans. Carried primarily by rodents, the virus causes fever, fatigue, nausea and breathing difficulties in infected humans. Transmission usually occurs through contact with, or inhalation of, rodent droppings and urine. There are two major disease-causing variants. The Asian hantaviruses result in a renal syndrome, primarily affecting the kidneys and blood vessels. The American hantaviruses, such as the Sin Nombre virus in the American Southwest or the Andes virus found on the cruise ship, cause hantavirus pulmonary syndrome, a condition affecting both the lungs and heart.Cleaning enclosed or poorly ventilated spaces where rodent droppings may be present, and thus can be inhaled, increases the risk of exposure, as does sleeping in dwellings frequented by rodents. Betsy Arakawa, the wife of the well-known actor Gene Hackman, is believed to have died of hantavirus pulmonary syndrome in their New Mexico home, where she may have been exposed to deer mouse droppings. Investigations following her death in early 2025 found rodent nests in several buildings on their property. Tragically, her husband, who died of natural causes just a week later, may not have known of her death, as he himself was in the late-stages of Alzheimer’s disease.Although infections are relatively rare, the fatality rate ranges between 30% and 50%. The global burden of hantavirus infection is dominated by China and Korea, where the less virulent Asian strain accounts for about 100,000 cases annually. The few cases reported in India are also of this strain. Notably, the Andes strain involved in the cruise ship outbreak is the only known version of hantavirus capable of direct human-to-human transmission. There is no known cure or vaccine. A prior Andes strain outbreak occurred in Epuyen, Argentina, between 2019 and 2019. It produced 29-34 cases and led to 11 deaths. The incident was extensively studied and until the Hondius outbreak, it was the best-characterised Andes strain outbreak on record. The sourceWhere could the virus have come from? The first suspect was the ship itself. A rodent infestation on a rigorously inspected, high-end cruise-ship was unlikely and was quickly ruled out. A more promising clue came from the first death or that of the ‘patient zero.’ The Dutch passenger and his wife had spent two months, before boarding the ship, travelling across parts of South America, including Chile and northern Argentina. In days leading up to the embarkation in Ushuaia, they spent time birdwatching at a prominent local landfill, known among birdwatchers worldwide as one of the few places where the white-throated caracara, or Darwin’s caracara, can be spotted. It is possible that the couple may have inhaled particles from the faeces of long-tailed pygmy rice rats present at the site. These rodents are known to carry the Andes strain of the hantavirus. The responseOn May 3, the MV Hondius reached the vicinity of Cape Verde, whose health authorities refused to allow docking at the port of Praia, citing public safety concerns. Three passengers were exhibiting high fever and/or gastrointestinal symptoms by then, including the doctor who had treated the first patient. They were evacuated by air. On May 5, the Spanish Ministry of Health announced that Spian had agreed to allow the ship to proceed to the Canary Islands, given Cape Verde lacked the facilities to isolate passengers from the local population and provide treatment if required. “The World Health Organisation explained that Cape Verde is unable to carry out this operation,” a spokesperson for the Spanish health ministry said, adding that “Spain had a moral and legal obligation to assist these people, among whom are also several Spanish citizens.”The cruise ship anchored for a few days in Tenerife, Canary Islands. Belgium, France, Germany, Ireland, the United States, the United Kingdom and the Netherlands sent planes to evacuate their nationals. In an unusual move, the Director-General of WHO, Dr Tedros Adhanom Ghebreyesus, travelled to the islands personally and wrote a letter to the people of Tenerife, assuring them that the risk was low. He wrote, “It is not common for me to write directly to the people of a single community but today I feel it is not only appropriate, it is necessary. I want to speak to you directly, not through press releases or technical briefings, but as one human being to another because you deserve that.” He thanked the Spanish government for what he called “an act of solidarity and moral duty.” The evacuation itself was carefully choreographed. Passengers were met and escorted by workers in full protective gear and driven to the airport along specially designated routes. The last six passengers, together with a few crew members, disembarked before the MV Hondius departed Tenerife for the Netherlands.As of 12 May, there are 11 cases linked to the outbreak, including three deaths. Nine of the 11 have been confirmed through laboratory testing, while two are classified as probable. All are passengers or crew from the ship. Epidemiological LessonsThis has been, at least so far, a localised outbreak initiated by the original Dutch passenger. Genetic sequencing of the virus across those who tested positive was identical, indicating a single source of infection. The timing of subsequent infections and the incubation periods observed are consistent with what was known from previous Andes strain outbreaks.The conventional understanding of hantavirus transmission has been that it requires close, even prolonged, contact. Much of the current discussion focuses on what exactly “close contact” means in practice. Some diseases, like HIV and Ebola, transmit through an intimate exchange of bodily fluids. SARS-CoV-2 or the virus causing COVID-19, on the other hand, is a respiratory virus that travels within droplets produced when an infected person coughs, speaks, sings or sneezes. The word “droplet” itself spans a variety of scales, ranging from aerosols, tiny drops that can stay suspended in the air for long periods to heavier droplets that fall quickly. The use of different words (aerosol versus droplet) can obscure the fact that these are really points on a continuum. Evidence suggests that the hantavirus behaves as an airborne pathogen, with transmission likely occurring through droplets in ways similar to SARS-CoV-2. Why it seems, for now, to transmit less efficiently remains an open question. As Heather McSharry noted in her blog,“this is one place where public-health language often collides badly with how the rest of us interpret words emotionally. Because listeners hear:’close contact’ and mentally translate it into:’only family members hugging each other for hours.’ While public-health investigators may simply mean: repeated indoor interactions, shared cabins, caregiving exposure, extended conversations, or cumulative time spent near an infectious person.”Geopolitical backdropThe United States officially withdrew from the WHO in January 2026 after being its largest funder for several years. The Trump administration cited the organisation’s handling of the COVID-19 pandemic and argued that the US was bearing a disproportionately large share of the WHO budget relative to what it received in return. The US terminated all funding and related in-kind support upon withdrawal, leaving without paying a substantial portion of its outstanding dues. However, some forms of technical cooperation and information sharing between US health agencies, including the CDC, and the WHO continue for now. Formal, high-level collaborative scientific initiatives have been restricted but technical information sharing for urgent threats continues. The loss of US funding has had serious consequences for global health initiatives, particular those focused on HIV/AIDS and tuberculosis. The African continent has been especially hard hit. Many grants focused on infectious diseases and pandemic preparedness have also been cut. Concomitant cuts in US public health research infrastructure, particularly to the funding of global programmes, have further weakened the country’s ability to coordinate, let alone lead, any outbreak response.The intersection of domestic politics and outbreak management raises specific questions. It is unclear whether the US will be able to impose stringent, unilateral quarantine requirements on American passengers returning from the MV Hondius, given the broad domestic opposition to government health mandates, that came to the fore during the COVID-19 pandemic and likely played a role in Trump’s reelection. A number of US-based passengers had left the ship before the outbreak was announced. While they have been instructed to isolate, mandatory quarantines have not been imposed. Some of these individuals may have travelled internationally again after returning to the US. Currently, all those who disembarked at Tenerife have been quarantined together at a single facility and will be released into home isolation once they have ridden out the quarantine period and tested negative. The quarantine is, however, voluntary. In the coming weeks, as the suggested 42-day post-exposure window elapses, the situation should become clearer. The ‘smoking gun’ for an outbreak slipping out of control would be cases of the Andes strain that cannot be connected to anyone on board. If the number of such cases expands steeply, it would imply a ‘community transmission,’ a term all-too familiar from the COVID-19 times. For now, nothing indicates that this will be the case.India’s positionIndia’s Ministry of Health and Family Welfare is the nodal ministry for public health matters. Under it falls the Directorate General of Health Services (DGHS), the National Centre for Disease Control and the Integrated Disease Surveillance Programme, the primary institutions charged with outbreak response. The extensive protocols devised by the WHO in collaboration with national organisations provide a precisely laid-out course of action in the event of a potential outbreak. While the Hondius’ passengers were almost exclusively of American and European origin, the crew was a more internationally diverse group. Two crew members were from India, with the majority from the Philippines. The Indian crew members will likely complete their quarantine in the Netherlands and thereafter, following further tests, should be able to return to India without additional restrictions. There appears to be no direct risk to India at the time. Conspiracy theories and misinformationThe fact that such an outbreak could be addressed, relatively easily, is because of the nature of the ship itself. Ships offer a national quarantine environment: passengers cannot get on and off at will, supplies can be brought in as needed and the vessel can remain at sea for extended periods. The only risk being that some passengers may fall so ill that they cannot be treated on the ship.Misinformation, conversely, poses a widespread threat. The internet is already awash with conspiracy theories, some implicating pharmaceutical or vaccine companies, while others hint at forms of biological warfare. It is here that governments and their agencies must be especially careful. Public communication must be clear, regular, definitive and authoritative. Conspiracy theories are a symptom of distrust, of governments, of companies and of expertise itself. Public health cannot function effectively in such a background. Dealing with misinformation means honestly acknowledging what is known and what is not. This is not evidence of a vast cover-up, but of the way science functions, at the liminal borders between the known and the unknown. Communicating uncertainty frankly while remaining realistic, even as the public seeks definite answers, is difficult. It is, however, an indispensable part of good public health communication. India’s COVID-19 experience was, in many ways, wanting in this regard. International collaborations remains crucial to global health. We need multilateral agencies to capable of dealing with problems that do not recognise borders, pandemic diseases being only one of them. Climate change and environmental pollution are others.The WHO’s actions and communications in response to the hantavirus outbreak have, at least so far, been exemplary. Establishing and reinforcing the WHO’s intellectual and financial independence should be a priority for the nations of the world.Gautam I. Menon is a Professor of Physics and Biology at Ashoka University. The views expressed here are his own and do not represent those of his institution.