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, as the World Health Organization predicted a “limited” spread of the virus if public health measures were implemented.

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

In the Netherlands, a Dutch flight attendant was undergoing testing for the hantavirus at a hospital on Thursday after she came into contact with an infected person, the Dutch health ministry said.

Dutch media outlets reported that the flight attendant worked for KLM Royal Dutch Airlines. The company declined to comment, citing privacy considerations for its employees.

Authorities did not say if the flight attendant was showing symptoms or whether she had worked on a flight that one of the victims of the cruise ship outbreak had briefly boarded the day before dying. That victim, a 69-year-old Dutch woman, died on April 26 in Johannesburg, South Africa.

The day before she died, the woman boarded KLM Flight 592 from Johannesburg to Amsterdam and spent about an hour on the plane, according to the airline. Barbara de Beukelaar, a passenger on that flight, said in a phone interview that the woman had been helped onto the plane in a wheelchair.

Airline staff members tended to the woman and decided to remove her ahead of the nearly 12-hour flight’s departure because of her health, according to KLM.

“Nobody on board thought that they were dealing with a contagious virus,” Ms. de Beukelaar said.

KLM said that it had handed over the flight’s passenger list to Dutch health authorities for contact tracing.

The Hondius — carrying almost 150 passengers and crew from almost two dozen countries — was on its way Thursday to the Canary Islands after three people who may have been infected with the virus were evacuated to the Netherlands.

The ship will not dock in the Canary Islands, but will remain anchored offshore until passengers are transferred by boat to Tenerife for evacuation flights to their countries, the Canary Islands authorities said. The ship is expected to arrive there on Sunday.

Oceanwide Expeditions, the Dutch company operating the cruise, said in a statement on Thursday that two of the people evacuated to the Netherlands were crew members with symptoms, a 56-year-old British national and a 41-year-old Dutch citizen.

A 65-year-old German woman without symptoms was also evacuated. She is undergoing tests in Germany, according to Düsseldorf University Hospital.

Dr. Jeanne Marrazzo, the head of the Infectious Disease Society of America, told reporters on Thursday that “our level of concern should be really high” but urged people not to panic.

“It’s not the situation where it’s going to start an outbreak everywhere in the world, across the world, from probably these sort of little kindling cases,” she said. “We don’t know that yet, but we really have to sort of try to just be calm and focus on the context and look at the risk in those situations.”

Tracing everyone who may have come in contact with those sickened by the virus could prove challenging.

On April 24, 30 people from at least 12 different countries disembarked from the ship in St. Helena, a remote island in the South Atlantic. That was more than a week before the first confirmed case of the virus was reported, according to Oceanwide.

The company said it had contacted the people who disembarked in St. Helena. At least one of them, a man in Switzerland, was receiving care in a hospital in Zurich and had tested positive for the virus, according to the W.H.O.

“We are working to establish details of all passengers and crew who embarked and disembarked” the ship since March 20, Oceanwide said.

In Singapore, two people who had been on the ship were in isolation and being tested for the virus, according to the National Center for Infectious Diseases. In Denmark, local health authorities said that a Danish passenger of the ship who had not been tested for the hantavirus was self-isolating without any symptoms.

In the United States, residents in three states were being monitored for potential hantavirus infections after being on the ship, officials said. None of them had symptoms, the officials said.

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