Investigators probing the hantavirus outbreak aboard the cruise ship MV Hondius have narrowed the likely origin to the Andes Cordillera region in northern Argentina and Chile, ruling out an earlier theory that a bird-watching visit to a landfill in southern Argentina was the source, according to reporting by ABC News and the BBC.
Dr. Boris Pavlin, team lead for field and humanitarian epidemiology at the World Health Organization, said the evidence points clearly toward rodent transmission in the Andes Cordillera, where the long-tailed rice rat, the known carrier of the specific strain involved, is common.
"There's absolutely every reason to believe that this came from rodents," Pavlin said.
He confirmed that WHO has traced the first hantavirus cases on board to passengers who had previously traveled to that region, though the precise location of exposure has not yet been identified.
"We expect that exposure happened in one of those locations. The exact location isn't obvious yet," Pavlin said.
One theory that circulated online and was initially raised by Argentinian officials held that a couple who became infected had contracted the virus at a landfill bird-watching site in Ushuaia, at the southern tip of Argentina. That theory has since been largely set aside. Dr. Omer Awan, a senior public health contributor for Forbes, told ABC News that the Andes strain of hantavirus requires direct inhalation of bodily particles from infected rodents, particularly in enclosed spaces.
"Bird watching is not going to lead to the Andes strain," Awan said.
Health officials also noted that the couple who visited the landfill had also traveled to Patagonia, more than a thousand miles north of the bird-watching site. Argentina has recorded more than 100 hantavirus cases and more than 30 deaths this year, and the rice rat associated with the disease is not present in all regions of the country.
Three people have died in connection with the outbreak on the MV Hondius. An elderly Dutch man died before he could be tested, his wife died after disembarking, and a German woman died on board the ship. Two of the three deaths were confirmed hantavirus cases, the BBC reported.
Eighty-seven passengers from the Dutch-operated vessel, which was docked in Spain's Canary Islands, have been repatriated over recent days. A group of 22 passengers, including 20 British nationals, a German national who is a UK resident, and a Japanese passenger, are more than 24 hours into a 72-hour isolation period at Arrowe Park Hospital in Merseyside, England. Once discharged, they will be asked to self-isolate for up to 45 days.
Ten additional passengers from the UK Overseas Territories of Saint Helena and Ascension Island are being brought to England as a precautionary measure. None of them are currently showing symptoms. The UK Health Security Agency said the National Health Service in England was well equipped to respond if any of them become unwell.
WHO Director-General Tedros Adhanom Ghebreyesus said Tuesday that "there is no sign that we are seeing the start of a larger outbreak," but cautioned that "given the long incubation period of the virus, it's possible we might see more cases in the coming weeks."
Awan stressed that public health officials' most pressing task remains containment.
"The more important public health conversation here is to make sure the virus is contained," he said. "It would be the icing on the cake if we found out where the origins are."
