An outbreak in rural communities 30 years ago in the Patagonia area of Argentina led scientists, for the first time, to document person-to-person transmission of hantavirus, which until then had been known only to spread through contact with rodents.

Nearly a decade ago another outbreak, also in Patagonia, provided detailed evidence of inter-human transmission when an infected 68-year-old rural worker attended a birthday party in a small village. The infection spread and resulted in 11 deaths.

These cases are being recalled after three people died from the virus on the Dutch cruise ship MV Hondius that departed from Argentina bound for Cape Verde.

Although it is not yet confirmed how the passengers were infected, a hypothesis being investigated by the World Health Organization (WHO), which has already categorically ruled out an epidemic, is that transmission occurred before boarding, placing the South American country under global scrutiny.

Tests on passengers who survived also confirmed they were infected with the Andes strain, the only strain in which human-to-human spread has been documented and which is found mainly in parts of Argentina and Chile.

However, Argentinian scientists who have studied the virus for decades agree that despite a slight recent increase in cases, Argentina is not facing anything significantly new or different from previous decades.

“Argentina is used to dealing with hantavirus,” said Dr Roberto Debbag, an infectious disease specialist and vice-president of the Latin American Society of Vaccinology, noting that the country made reporting hantavirus infections mandatory after the 1996 cases. “Since then, there have always been cases and outbreaks … but nothing has really changed.”

Since July last year, Argentina has recorded 101 hantavirus cases, with 32 deaths; in previous epidemiological seasons, between July and June, the figures were lower, such as 64 cases and 14 deaths in 2024-25 and 82 cases and 13 deaths in 2023-24.

Dr Raúl González Ittig, a biologist and professor at the National University of Córdoba, said he believed the increase was more closely linked to rodent behaviour, noting that there was a significant drought in 2023 and 2024, followed by increased rainfall in subsequent years, which meant greater vegetation cover and more food for the animals.

“Global climate change is altering everything, and that could also lead to hantavirus cases emerging in places where they had not previously occurred,” he said.

Even with the rise, Argentina remains within its historical annual average of about 100 cases – far below, for example, China and the Republic of Korea, where there are thousands of cases annually according to the WHO.

The vast majority of up to 100,000 annual hantavirus cases occur in Asia and Europe, but the key difference lies in the severity caused by different strains: while in those regions the fatality rate is up to 15%, in the Americas it can reach 50%.

Nevertheless, the WHO has said the risk of hantavirus to the general population is “absolutely low”, noting that person-to-person transmission does not occur easily.

Even though it is far from leading global case numbers, Argentina still has the highest total in Latin America, which scientists attribute to the climate crisis and ecological imbalances such as the loss of natural predators.

To determine where contamination on the MV Hondius may have occurred, Argentina’s health ministry plans to capture rodents for analysis along the route taken by the Dutch couple who first developed symptoms. They had been in the country since 27 November, making multiple car journeys, including trips to Chile and Uruguay, before boarding the ship on 1 April from the port of Ushuaia.

The ministry has reiterated that it is “not confirmed that the infection occurred in Argentina” and notes that in the province from which the ship departed, Tierra del Fuego, there has not been a confirmed case of hantavirus in the past 30 years.

On Thursday, the WHO director general, Tedros Adhanom Ghebreyesus, said Argentina should “reconsider” the decision taken by its president, Javier Milei, and formalised in March to leave the organisation, following the example of his US ally, Donald Trump.

Addressing the US and Argentina, Ghebreyesus said “viruses don’t care about our politics and they don’t care about our borders” and that “solidarity is our best immunity”.

For Ittig, Milei’s decision to leave the WHO is yet another facet of the problems caused by the libertarian’s “chainsaw” policy of deep spending cuts in science, education and healthcare, which could affect efforts to combat hantavirus.

“The experience and knowledge to tackle the hantavirus exist, and Argentina has them,” he said. “The problem is that investment is needed – and that is not what is happening now.”