How was hantavirus transmitted? A visual explanation of the ‘MV Hondius’ outbreak

The first patient involved in the hantavirus outbreak boarded a ship in Ushuaia, Argentina, unaware that he was carrying the virus that would trigger a health crisis. The passenger and his wife, both Dutch, had been traveling around Argentina for weeks before boarding the MV Hondius, an expedition ship. The leading hypothesis is that they “were infected off the ship,” according to the WHO.

The first case. The man began experiencing symptoms on April 6 — fever, headache, mild diarrhea — a few days after the ship departed Ushuaia to begin its Atlantic crossing on April 1. The virus’s incubation period lasts between one and six weeks, hence the suspicion that he was already infected when he boarded.

The second case. The first patient died on April 11. His wife, who shared a cabin with him, developed symptoms on April 24 (case 2). That same day, another man went to the ship’s doctor with a fever and symptoms of pneumonia (case 3). The WHO considers two possibilities: that the woman was also infected in Argentina before boarding or that her husband infected her during the voyage.

Disembarkation. On April 21, 23 passengers disembarked on Saint Helena, unaware of an outbreak that had not yet been detected. Four days later, the sick woman (case 2) was evacuated from the same island on a flight to Johannesburg, South Africa: her condition deteriorated during the journey and she died the following day. Case 3 disembarked on Ascension Island and on April 27 also flew to South Africa, where he remains hospitalized in the ICU.

All of this takes place without anyone knowing there are cases of hantavirus on board. Confirmation comes on May 2, when a PCR test detects the infection in patient 3, hospitalized in Johannesburg. Two days later, the illness is also confirmed in case 2.

Then contact tracing begins on their flights and also among disembarked passengers, as a WHO spokesperson confirmed to EL PAÍS: “international contact tracing is underway.”

Meanwhile, new cases of infection continue to appear on the ship. Case 4 is a woman who began experiencing symptoms — fever and malaise — on April 28 and died on May 2. Cases 5, 6, and 7 remained on board for several days with high fever and gastrointestinal symptoms before being evacuated this Wednesday.

The eighth case, and for now the last, is a Swiss citizen who disembarked with his wife before the outbreak was detected and is being treated in Zurich.

How did patient 1 become infected?

Passengers could have been infected by rodents on the ship, but that possibility now seems unlikely: “We are told there are no rodents on board,” explained Maria Van Kerkhove, WHO’s lead expert on epidemic and pandemic prevention and preparedness.

The organization assumes that the initial patients, the first case and his wife, were infected before boarding the ship: “They boarded in Argentina. And with the incubation period for hantavirus, which ranges from one to six weeks, our assumption is that they were infected off the ship, perhaps while doing some activity there,” Van Kerkhove explained.

Hantavirus is a known, though uncommon, virus present in several countries in the Americas. According to the Pan American Health Organization (PAHO), 229 cases were detected in the region in 2025, 66 of which were reported in Argentina. The Andean variant circulates in Argentina, and cases of human-to-human transmission through close contact have been documented.

Hantavirus has a high fatality rate: in 2025, 26% of confirmed cases in the Americas resulted in death. The Andean strain, identified in the outbreak on the MV Hondius, is responsible for the majority of cases in Argentina, where the fatality rate observed in 2025 was 32%. However, unlike Covid-19 or the flu, it is not easily transmitted between people.

Humans are usually infected through rodents. Many people who become ill are those who have contact with infected animals, inhaling aerosols containing viral particles present in urine, feces, or saliva.

However, person-to-person transmission is also documented. It is rare and has only been demonstrated with the Andean variant. It requires close and prolonged contact, such as between family members or partners.

An indication of its limited transmissibility is the cruise itself: although 147 people have shared enclosed space on the vessel for weeks, only eight cases have been reported on board.

The WHO maintains that “the overall risk to the public is low,” but the organization has activated protocols: an infectious disease specialist from the European Centre for Disease Prevention and Control (ECDC) has joined the ship, symptomatic passengers have been evacuated to European hospitals, and the WHO is conducting international contact tracing of those who have already disembarked. The virus’s incubation period can last up to six weeks; until then, the possibility of new cases appearing among the passengers who have already disembarked cannot be ruled out.

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition