Eight people infected in the hantavirus outbreak aboard the MV Hondius cruise ship have tested positive for the Andes virus, the only strain transmitted between humans, the World Health Organization said Wednesday.

"Eight cases were laboratory-confirmed for Andes virus (ANDV) infection, two are probable, and one case remains inconclusive and undergoing further testing," the UN health agency said in its latest update on the outbreak.

Three people from the ship have died since it set sail from Argentina on April 1 for a cruise across the Atlantic Ocean.

Two of the victims had confirmed Andes virus infections, and the third is listed as a "probable" case, according to the WHO.

Hantavirus typically spreads from the urine, faeces and saliva of infected rodents.

There are no vaccines or specific treatments for the rare disease.

All known cases in the current outbreak were people aboard the cruise ship.

The case listed as inconclusive is an American passenger repatriated to the United States, who is "currently asymptomatic" and undergoing further testing after one positive and one negative result, the WHO said.

It maintained its assessment of the public-health risk from the outbreak at "moderate" for those who were on the ship and "low" for the rest of the world.

The origin of the outbreak is still unknown.

The WHO says the original infection happened before the cruise, because the first victim, a 70-year-old Dutch man, started showing symptoms on April 6, while the virus' incubation period is one to six weeks.