A mass hantavirus infection has broken out on a large cruise ship anchored off an island nation in West Africa. Spread by rodents, the virus causes severe illness in humans and can have a fatality rate of up to 50%. Three passengers have already died, but the exact identity of the virus and the route of transmission have not yet been clearly determined.
The World Health Organization (WHO) said on the 4th that "a cluster of severe respiratory illness cases was reported on the 2nd (local time) from the Netherlands-flagged cruise ship MV Hondius." According to WHO, as of the 4th, seven cases have been confirmed, with three deaths and one person in critical condition.
The MV Hondius departed Ushuaia, Argentina, on Apr. 1 and crossed the South Atlantic. Along the way, it called at Antarctica, South Georgia, Nightingale Island, Tristan da Cunha, Saint Helena, and Ascension Island. The ship, currently anchored in the waters of Cabo Verde, has 147 passengers and crew from 23 countries on board.
◇ Seven infected and three dead in a month
Hantavirus is a zoonotic infection in which viruses in the excreta, saliva, or urine of rodents such as striped field mice and house mice become aerosolized (fine particles) and are inhaled through the respiratory tract. It mainly causes fever and flu-like symptoms, but in severe cases it can be fatal. According to WHO, the case fatality rate of hantavirus infection is less than 1–15% in Asia and Europe, but reaches up to 50% in the Americas.
The first case on the cruise ship appeared on Apr. 6. A 70-year-old Dutch man began to have a fever and died on board five days later. The cause of death at the time was not clearly identified. His wife, who was traveling with him, disembarked with his body on the 24th of last month on Saint Helena, an island east of Africa. She was flown toward Johannesburg, South Africa, but her condition worsened en route and she was taken to the emergency room, where she died on the 26th.
Another case emerged on the cruise ship on Apr. 24. A British man fell ill and was transferred to South Africa. The National Institute for Communicable Diseases of South Africa examined the patient's sample and confirmed hantavirus infection. An 80-year-old woman who had shown flu-like symptoms since the 28th of last month died on the 2nd. WHO said three suspected patients with high fever or gastrointestinal symptoms remain on board. South African medical staff have collected specimens from the patients and are testing them.
Hantavirus returned to public attention after a 1993 outbreak in the U.S. Southwest that killed 13 people. The virus falls into two major groups. Old World hantaviruses are found in Africa, Asia, and Europe and cause hemorrhagic fever with renal syndrome (HFRS). New World hantaviruses are found in the Americas and cause hantavirus pulmonary syndrome (HPS). The current cluster is suspected to have been caused by a variant of a New World hantavirus.
◇ Exposure to the virus suspected in Argentina
Hantavirus is transmitted from rodents to humans, but there are rare variants that spread between people. One is the Andes virus, a variant of a New World hantavirus. Experts suspect the cruise ship passengers were infected with the Andes virus, first identified in Chile and Argentina in 1995.
The MV Hondius began its voyage in April, and its point of departure was Argentina, where the Andes virus had been circulating since last year. In Argentina, between July 2025 and January 2026, at least 20 people died from this virus.
The number of hantavirus cases in Argentina was similar to previous years, but the fatality rate increased. According to the Argentine Ministry of Health, between January 2025 and January 2026, 34% of infected people died. This is higher than the national average annual fatality rate of 10–32% recorded each year from 2019 to 2024.
Rhys Parry, a virologist at the University of Queensland, told Science, "Because symptoms often appear one week to one month after exposure to hantavirus, more cases may emerge in the coming days or weeks."
It is still unclear whether passengers were infected with hantavirus before boarding or were exposed to the virus on board. The ship is currently reported to be free of rats, raising the possibility that someone infected on land transmitted it to close contacts. However, Korea University medical school professor Chung Jae-hoon said, "Human-to-human transmission is a possibility, not a certainty."
Chung said, "If multiple passengers fall ill at staggered times, it can look as if transmission occurred from one patient to the next," adding, "The Andes virus may spread not via rodents but through consumption of contaminated food or inhalation of aerosols through ventilation systems, so it is also necessary to look for viral genomes in environmental samples." He also advised that assessing the first decedent's movements before departure and the spatiotemporal contact among cases should proceed in parallel to identify true person-to-person transmission.
◇ Will it become a "floating petri dish"?
When virus infections occur on a ship during a voyage, they can trigger a cluster. The Diamond Princess incident in Apr. 2020 is a prime example. On the large cruise ship anchored at Yokohama, Japan, 712 of 3,711 aboard tested positive for COVID-19, and 14 died.
The incident drew attention because early response failed and close contact among passengers caused explosive growth in cases. People called the ship a "moving coronavirus island" and a "floating petri dish of viruses." Norovirus, which causes food poisoning in winter, can also spread rapidly on board and cause clusters of gastroenteritis.
There is still no established response to a hantavirus cluster. Pablo Vial, a doctor who treated hantavirus patients in Chile, told the international journal Nature, "There is virtually no established protocol for those exposed to the virus." WHO has not yet decided how to handle the 147 asymptomatic passengers isolated on the ship.
Maria Van Kerkhove, acting head of WHO's infectious disease management, said, "It is a plausible hypothesis that the Andes virus is the cause," but added, "This virus rarely spreads directly between people, and the risk of large-scale spread is low." She said, "WHO does not consider this a pandemic, but we are indeed exercising our authority to advise on public health events."
◇ Korean scientist developed the first vaccine
There is no specific treatment for hantavirus. Supportive care to alleviate symptoms can save lives. Hantavirus infection causes vascular leakage, leading to fluid accumulation in the lungs. This can deprive the heart of the ability to pump enough blood throughout the body. Fortunately, these changes last only a few days. During this period, extracorporeal membrane oxygenation (ECMO) can temporarily replace the function of the heart and lungs.
ECMO draws blood from a patient's veins, oxygenates it in an external device, and removes carbon dioxide. Chile has a policy of immediately transferring all patients who test positive for hantavirus to medical centers equipped with ECMO.
Hantavirus has deep ties to Korea. Lee Ho-wang (1928–2022) studied an unknown hemorrhagic fever that was spreading among U.S. troops during the Korean War and in 1976 first identified the virus causing the disease in the lung tissue of rats. He named it Hantaan virus after the Hantan River, where it was found. He later identified Seoul virus and established the genus Hantavirus.
Lee led vaccine development and in 1990 produced Hantavax, the world's first vaccine to prevent hemorrhagic fever with renal syndrome. However, the vaccine can be used against Old World hantaviruses in Korea or China, but it is ineffective against the New World hantaviruses suspected to have infected the cruise ship passengers in this outbreak. No New World hantavirus vaccine has been developed, because the low prevalence of infection has made it difficult to recruit patients for clinical trials.
References
WHO (2026), https://www.who.int/emergencies/disease-outbreak-news/item/2026-DON599