Health officials in a growing list of countries scrambled on Thursday to track people connected to a deadly outbreak of the hantavirus on a cruise ship. The World Health Organization also predicted a “limited” spread of the virus if public health measures were enacted.

“This is not Covid, this is not influenza,” Dr. Maria Van Kerkhove, the W.H.O.’s head of epidemic and pandemic preparedness, said on Thursday at a news conference in Geneva. “This spreads very, very differently.”

Human-to-human transmission of the hantavirus, a family of viruses carried by rodents, is rare. The Andes strain of the hantavirus, which has been confirmed in cases tied to the cruise ship, is the only one known to spread from human to human, but it is transmitted primarily through close personal contact, Dr. Van Kerkhove said.

“This is not the start of an epidemic, this is not the start of a pandemic,” she said.

Since April 11, three passengers who were aboard the MV Hondius, a Dutch-flagged cruise ship, have died and at least five other people have been sickened after showing symptoms of the hantavirus, according to the W.H.O. Health officials have confirmed five cases of the hantavirus on the ship so far, all of them involving the Andes strain, which is primarily found in South America.

People in several countries are now being tested or monitored after possibly being in contact with the virus.