"This virus is not new to the world," U.S. virologist Thomas G. Ksiazek said. "If it were going to become an epidemic, it would have happened a long time ago."

BRUSSELS, May 12 (Xinhua) -- A hantavirus outbreak aboard a polar expedition cruise ship has killed three people, raising fears of a new pandemic. Though new cases may still surface during the virus's incubation period of up to six weeks, global health authorities and experts say the risk of broader spread remains low.

World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus arrived in Tenerife, Spain, on Saturday to oversee the evacuation of the ship's remaining passengers and coordinate public health operations, stressing that the incident "is not another COVID pandemic."

HOW THE VIRUS SPREADS

As of Tuesday, the WHO had reported 11 hantavirus cases linked to the ship, including three deaths. Of the 11 cases, nine have been confirmed as Andes virus infections, with the remaining two classified as suspected. The Andes virus is a hantavirus strain that spreads from person to person.

The ship was carrying around 150 passengers and crew members from more than 20 countries, including 38 from the Philippines, 23 from Britain, 17 from the United States, 14 from Spain, 11 from the Netherlands, eight from Germany, and five each from France and Ukraine.

Argentine officials said that the most likely source was a couple who visited a landfill during a bird-watching excursion in Ushuaia, Argentina, before boarding, where rodents carrying the virus may have been present. In a statement on Wednesday, the local health authorities said that they will conduct rodent capture and analysis in Ushuaia.

The 70-year-old husband died aboard the ship on April 11. His 69-year-old wife disembarked during a stop in St. Helena and later tested positive for hantavirus after flying to Johannesburg. Local health authorities said that the flight has led to 22 French contacts, a foreign national in Indonesia, and two Spanish contacts being placed under medical monitoring.

So far, no case has been confirmed among individuals who never boarded the ship but were only on the same flight.

Hantavirus was first isolated and named in 1978 after South Korea's Hantan River, where an outbreak occurred among soldiers during wartime.

According to the U.S. Centers for Disease Control and Prevention (CDC), humans usually contract hantavirus through contact with infected rodents or their saliva, urine and droppings, most commonly by inhaling virus particles emitted into the air from contaminated waste. Rodent bites can also transmit the virus.

PASSENGER EVACUATION

The ship arrived off the coast of Tenerife in Spain's Canary Islands on Sunday, anchoring about 500 meters from shore. Passengers in hazmat suits were ferried ashore in small boats and taken directly to the airport for government-chartered flights.

As of Sunday, 94 passengers from 19 countries had been evacuated. Spain, the WHO, and multiple countries coordinated the operation. The final evacuation flight departed on Monday, carrying Australian and Dutch nationals.

Quarantine requirements vary. Spain transferred its nationals directly to a military hospital for forced isolation, while France and Britain have adopted similar 72-hour facility observation plus extended at-home monitoring.

Health authorities have confirmed that among the evacuees, one Spanish passenger is asymptomatic after an initial positive test, a French passenger tested positive and developed symptoms on the flight to Paris, and a U.S. citizen returned a weak positive result.

With 26 crew members still on board, the ship has set sail for Rotterdam in the Netherlands for thorough cleaning and disinfection. It is expected to arrive on Sunday.

Cruise ships are called "floating cities" for good reason: Thousands of people share the same air, dining areas, elevators, and entertainment spaces for days at a time. Once an infection gets onboard, it moves quickly through shared surfaces and close contact.

Besides, ventilation is often inadequate in cabins, restaurants, and indoor venues, accelerating transmission.

Before the outbreak was confirmed, some 30 passengers from about 12 countries had disembarked in St. Helena, a South Atlantic island, on April 22 to 24. The WHO has shipped 2,500 diagnostic test kits to multiple countries and issued operational guidance for contact tracing.

PANDEMIC RISK REMAINS LOW

The couple were the first two fatalities in the outbreak caused by the Andes virus, which belongs to the "New World" group of hantaviruses that cause Hantavirus Pulmonary Syndrome (HPS). Unlike "Old World" hantaviruses found in Europe and Asia, which cause Hemorrhagic Fever with Renal Syndrome (HFRS) with mortality rates ranging from about 1 to 15 percent, New World strains are significantly more lethal.

HPS has a fatality rate of up to 40 percent, with those caused by the Andes virus among the most deadly.

As a severe respiratory illness, HPS typically begins with fever, fatigue, and muscle aches, particularly in large muscle groups. About half of patients also develop symptoms such as headache, dizziness, nausea, vomiting, or abdominal pain. Within days, the condition can rapidly worsen, leading to coughing, shortness of breath, and fluid accumulation in the lungs.

About 38 percent of patients who develop respiratory symptoms die from HPS, often within 48 hours of hospitalization. The U.S. CDC noted that there is no specific antiviral treatment or widely available vaccine, and care is mainly supportive, including oxygen therapy and respiratory support.

However, unlike COVID-19 or influenza, hantavirus does not spread efficiently through the air. Its natural rodent hosts are also not present in Europe or North America, making sustained local transmission unlikely.

Transmission requires close, prolonged contact with severely ill symptomatic individuals. Asymptomatic carriers are unlikely to spread it, said Ivan Gentile, professor of infectious diseases at the University of Naples Federico II.

To become a pandemic threat, a pathogen often needs to keep people mobile and socially active during the infectious period, explained Zoe Weiss, director of Clinical Microbiology at Tufts Medical Center.

"This virus is not new to the world," U.S. virologist Thomas G. Ksiazek said. "If it were going to become an epidemic, it would have happened a long time ago."