How did hantavirus cruise ship outbreak start? What we know

Officials are continuing to investigate the origins of a hantavirus outbreak on a cruise ship that has left three people dead.

The MV Hondius ship anchored in Tenerife, Spain, on May 10, where crew and passengers, including 17 Americans, began evacuation. 

The American passengers have since returned stateside, with the majority of them quarantining in Nebraska where they will be monitored for symptoms. Two were sent to Atlanta for further assessment, officials said.

Hantavirus is a virus usually transmitted to people through contact with rodents' urine, feces or saliva. The strain at the center of the outbreak has been confirmed as the Andes virus, which is believed to spread person-to-person, according to the World Health Organization.

Here's what to know about the origin of the hantavirus outbreak.

How did the hantavirus outbreak start?

The WHO has said it believes the hantavirus outbreak stemmed from a Dutch couple on board the MV Hondius who both later died from their infections.

Prior to boarding the ship, the couple had gone on a bird-watching trip through Argentina, Chile and Uruguay, Dr. Tedros Adhanom Ghebreyesus, director-general of the WHO, said at a May 7 briefing.

The couple's bird-watching trip included visits to sites where "the species of rat that's known to carry hantavirus was present," he said.

Dr. Maria Van Kerkhove, director of WHO's department of epidemic and pandemic management, said at a May 5 briefing that the MV Hondius also stopped at many islands up the coast of Africa where others may have come in contact with the virus.

"We do believe that there may be some human-to-human transmission that's happening among the really close contacts – the husband and wife, people who've shared cabins, etcetera," Van Kerkhove said.

How is hantavirus transmitted?

Hantavirus is typically transmitted by contact with rodents, though officials have identified the strain in this outbreak as one that can spread person-to-person.

This strain, the Andes virus, is believed to spread between people who have had close contact – within six feet – for at least 15 minutes, Dr. Brendan Jackson, the acting director of the division of high-consequence pathogens and pathology at the Centers for Disease Control and Prevention, said at a May 11 news briefing.

"Typically, we're talking about exposure specifically to bodily fluids, and that could include things like saliva – so if you're sharing eating utensils, kissing, touching, those type of things – It can also mean just being really, really close to that person for a fairly long period of time," Jackson said.

Melina Khan is a national trending reporter for USA TODAY. Keep up with her on X @melinakh and Instagram @bymelinakhan.