The first cases, a Dutch man and his wife, who died nearly three weeks after him, had spent more than three months traveling through Argentina, Chile and Uruguay on a birding trip before they boarded the Hondius in Ushuaia, Argentina’s southernmost city, on April 1, according to the WHO.

That trip “included visits to sites where the species of rat that is known to carry Andes virus was present,” WHO Director-General Tedros Adhanom Ghebreyesus said at a Thursday briefing.

Landfill theory

Last week, The Associated Press, citing two Argentine officials investigating the origins of the outbreak, said the government’s leading hypothesis was that the couple contracted the virus while bird-watching in Ushuaia and may have been exposed to rodents at the city’s landfill.

The landfill theory made some birding enthusiasts uneasy and prompted some authorities, locals and others to defend Ushuaia, a city of nearly 85,000 that draws tourists to its Antarctic cruise ships and abundant, watchworthy bird population.

Esteban Daniels, a birding guide in Ushuaia, said the landfill attracts eye-catching birds — the white-throated caracara is a scavenger that finds easy meals there — not the hantavirus.

“I have been visiting the rubbish dump with birdwatchers for at least 25 years,” he said by email. “We always observe from outside the perimeter with binoculars and spotting scopes. We aren’t allowed to enter the site, which has a high fence around it and security at the entrance.”

“There isn’t really any need to go in, as we can see the White-throated Caracara, other caracaras, gulls and, occasionally, the Andean Condor from the side street,” he added.

Daniels said he guided some of the ship’s birding passengers at the landfill in the days before it left for multiple South Atlantic destinations, though he said the couple that died was not among them.

“None of them showed any signs” of being infected, he said by text.

‘Smear campaign’

Hantavirus is typically contracted through contact with the urine, droppings or saliva of infected rodents, like rats and mice.

The Andes variant of hantavirus is the only strain that can be transmitted from person to person, though health officials have reiterated that it is not Covid and does not spread like the pandemic virus. It is carried by the long-tailed pygmy rice rat, which is more common in points north of Ushuaia, experts have said.

The virus identified on board the Hondius is “near identical with the strain that recently caused a well-documented human-to-human outbreak in Argentina in 2018/19,” Spyros Lytras, an evolutionary virologist, said by email. That outbreak, in Patagonian Argentina’s Chubut province, petered out after 34 documented infections and 11 deaths.

On Friday, Juan Petrina, the province of Tierra del Fuego’s environmental health and epidemiology director, showed reporters a graph of hantavirus cases in the area and said that it was unlikely the first cases originated there.

“I’ve included data starting in 2000, but I can go back as far as you like,” Petrina said at the news conference. “There continues to be zero cases of hantavirus in our province.”

“The scarcity of this rodent, combined with the province’s historical health status and the short period of time during which this couple may have been exposed to these rodents, greatly reduces the likelihood that the infection occurred here,” Petrina said.

“I believe we are facing a smear campaign against this destination,” he added.

Attempts to contact the city of Ushuaia by email were not successful.

‘Impeccable’ hygiene measures

The definitive origin of the first infection has not been identified, and epidemiological investigations are underway, the WHO has said.

It said evidence has pointed to “subsequent human-to-human transmission onboard” the vessel.

Basanth Sadasivan, 28, who was on board the MV Hondius for a 22-day cruise in February, said the outbreak came as a surprise to him given the ship’s hygiene measures.

“The safety measures and hygiene measures on that ship were just simply impeccable, and they were so strict about everything,” he said in an interview. “Every time we got off the ship and we came back on, we would have to disinfect everything, all of our gear, you know, all of our boots, all of even our hiking sticks, would have to be disinfected.”

That process involved their items being sprayed down and a manual examination with brushes “to make sure that there are no stones and eggs like, you know, inside your boots inside your jacket,” Sadasivan said.

Passengers were also told to maintain a 3-meter distance (9.8 feet) from wildlife on land while on excursions, he said.

During one inspection, Sadasivan said, “my boot had this little stone in between the threads of the boot. And the person who was inspecting all of our gear made me take it back and get disinfected again, because she was saying that that little stone could contain something that causes disease.”

Oceanside Expeditions, which operates the Hondius, said on its website that it follows the guidance of the cruise industry and the requirements of each country that hosts the vessel.