NEW YORK -- Hantaviruses do not spread easily between people, which makes health officials confident the recent outbreak on a cruise ship that has killed three people will not turn into an epidemic.

But, still, they need to make sure. So health officials in several countries are contact tracing: trying to identify and follow people who may have come in contact with passengers who got sick or died.

Hantaviruses usually spread when people inhale contaminated residue of rodent droppings. While human cases are rare, small outbreaks have been documented around the world. But the Andes virus implicated in the cruise ship outbreak may be able to spread between people in rare cases. And viruses can change.

Scientists are trying to learn more about the virus as fast as they can, including whether it has mutated and how exactly it spreads.

The goal of contact tracing is to alert people who might have been exposed, keep tabs on them in case they come down with symptoms, and prevent them from spreading it to others.

The process isn’t easy because people are social and mobile creatures who spend time with others, visit crowded places and travel.

In the cruise ship outbreak, fewer than a dozen people are thought to have shown any symptoms, and there have been only five confirmed cases, but many more may have been exposed.

About 140 people remain on the cruise ship headed for the Canary Islands, where they will disembark, and none has been reported to be sick.

But authorities are trying to reach the dozens of people who left the ship about two weeks after a passenger died, but before authorities knew a hantavirus was the culprit. They were from at least 12 different countries, including from several states in the U.S. — including Arizona, California, Georgia and Texas, according to infectious disease experts and state public health officials.

Authorities in St. Helena — the remote, volcanic British territory in the South Atlantic where passengers got off — said they were monitoring a small number of people considered “higher-risk contacts.” They were being told to isolate for 45 days, the St. Helena government said.

British health officials say two people who were passengers aboard the ship but flew home midway through the journey are self-isolating but do not have symptoms. The U.K. Health Security Agency said “a small number” of contacts of the two are also self-isolating but not showing symptoms.

Singaporean health authorities said they were monitoring two men who disembarked at St. Helena and flew to South Africa and then home. The two men, who arrived in Singapore at different times, were being tested for hantavirus and were isolated at the country’s National Center for Infectious Diseases, officials said.

The U.S. government has released few details about its work on any contact tracing.

Texas officials on Thursday said public health workers there have reached the two people who left the ship April 24, who say they are not experiencing symptoms and did not have contact with a sick person while aboard. They promised to monitor themselves with daily temperature checks and contact public health officials at any sign of possible illness, officials said.

Arizona officials said they too are following a person who disembarked. They said they don’t know exactly when the person arrived in Arizona. The U.S. Centers for Disease Control and Prevention notified the state health agency on May 5, state officials said. That's when monitoring began and it will continue for 42 days.

Two Canadians who disembarked are in Ontario and have been advised to self-isolate since they returned home, the province’s health minister says.

Apart from tracking people, scientists are also trying to understand the germ. The Andes virus, a member of the hantavirus family found in South America, may be one of the rare hantaviruses that can spread between people. Officials in Argentina believe the first cases may have been contracted on a birdwatching trip in the southern city of Ushuaia.

Argentina’s Health Ministry has yet to dispatch the team, but scientists from the state-funded Malbrán Institute planned to travel to Ushuaia “in the coming days,” the ministry told The Associated Press.

Scientists are analyzing the virus's genetics to see whether it has changed in a way to make it more transmissible.

They are also trying to learn exactly how it spreads, said Dr. Jeanne Marrazzo, chief executive officer of the Infectious Diseases Society of America. They believe people are mainly infectious when they have symptoms, and, if the virus spreads, it may be transmitted through small liquid particles that blow out of an infected person when they talk, cough or sneeze. ___

AP journalists Isabel Debre in Buenos Aires, Argentina; Gerald Imray in Cape Town, South Africa; Rob Gillies in Toronto; Jill Lawless in London; Suman Naishadham in Madrid; Susan Montoya Bryan in Albuquerque, New Mexico; and Jamie Stengle in Dallas contributed.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.