USHUAIA — A hantavirus outbreak aboard the cruise ship MV Hondius has killed three people and sickened five others after the vessel departed Ushuaia, Argentina, last month. The first confirmed cases were a Dutch man and his wife who boarded the ship on April 1, according to the World Health Organization.

The couple had spent more than three months traveling through Argentina, Chile and Uruguay on a birding trip before boarding the MV Hondius, the WHO said. The man died, and his wife died nearly three weeks after him. The first person with a confirmed case may have been exposed to rodents while on a birding trip, the WHO said.

"The birding trip included visits to sites where the species of rat known to carry the Andes virus was present," WHO Director-General Tedros Adhanom Ghebreyesus said at a WHO briefing. The Argentine government's leading hypothesis is that the couple contracted the virus while bird-watching in Ushuaia and may have been exposed to rodents at the city's landfill, according to two Argentine officials. Rodents can carry hantavirus.

Ushuaia has a population of nearly 85,000 and draws tourists to its Antarctic cruise ships and bird population. Tierra del Fuego is a region well known for its biodiversity and bird-watching.

Esteban Daniels, a birding guide, guided some of the MV Hondius's birding passengers at the Ushuaia landfill in the days before the ship left for multiple South Atlantic destinations. The couple who died were not among the passengers he guided at the landfill. Daniels said the landfill attracts eye-catching birds such as the white-throated caracara, which 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," Daniels 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," he said. "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 said.