Hantavirus does not spread easily, but authorities may be downplaying the risks

Close, lasting contact.

Health officials have repeatedly said this is the only way the Andean hantavirus, which caused an outbreak on a cruise ship and drew global attention, could spread among people.

“You have to be in close contact with someone who has a lot of symptoms,” Dr. Jay Bhattacharya, deputy director of the Centers for Disease Control and Prevention, in an interview on Fox News.

But scientists who have been studying hantaviruses for decades are far less sure how the virus might behave.

They agree with health authorities that the Andean virus is not particularly contagious and is unlikely to cause a major outbreak. However, they said research has shown that the virus can be transmitted without direct contact in certain circumstances.

“It’s important to be scientifically honest and communicate that, otherwise you lose credibility,” said Steven Bradfute, a viral immunologist and hantavirus expert at the University of New Mexico.

In an interview, Dr. Tedros Ghebreyesus, director general of the World Health Organization, said officials have emphasized close contact as a way to spread the virus to avoid people panicking about rarer options.

“It’s very hard to explain to people that they say, ‘Okay, this is the exception, this is the norm,'” he said. “When you say it’s an exception, they might still think it’s a common occurrence too.”

The hantavirus outbreak that began last month on the Dutch cruise ship MV Hondius has so far sickened at least nine people and killed three. Many of the approximately 150 passengers, including 18 in the USA, are being closely monitored in quarantine. The remainder were given a range of instructions to avoid spreading the virus to others, including: take your temperature daily, avoid flying in commercial transport and try to use your own bathroom.

On Sunday’s CNN program “State of the Union,” Dr. Bhattacharya did not remember when some passengers who disembarked in St. Helena, an island in the Atlantic Ocean, on April 24 arrived on American soil. No one had symptoms at the time of the trip, he said, so officials saw no need to alert the public or trace contacts.

“The virus does not spread unless someone has active symptoms,” he said.

That’s not certain either, although some scientists believe that people are most contagious when they develop symptoms.

Some laboratories have been studying hantaviruses for decades, but there is still much that is not known about them because they grow slowly and are difficult to analyze genetically.

Hantaviruses occur naturally in rodents. The Andean virus, which is primarily found in Argentina, where the cruise ship began its journey, is the only known species of hantavirus that spreads among humans. But scientists were slow to acknowledge this possibility.

“It was very difficult to convince people of this, even here in Argentina,” said Valeria Martinez, a virologist at the National Institute of Infectious Diseases in Buenos Aires.

In the largest outbreak to date in Epuyén, Argentina, Dr. Martinez and her colleagues carefully examined transmission patterns in 34 cases and 11 deaths between November 2018 and February 2019.

The study confirmed that the virus does not spread easily: none of the 82 health workers caring for patients became infected, even though many of them were not wearing protective equipment.

But the researchers also identified so-called “super-spreading events,” in which a single person was able to transmit the virus to several others. The outbreak began after a man infected with rodents developed a fever and attended a birthday party with 100 guests.

“He was only there for 90 minutes because he felt sick,” said Dr. Martínez.

Within three weeks of the event, five people at the party had become ill. One of those five soon died, and his wife most likely passed the virus on to another ten people after his death. In total, six of the 34 cases in the outbreak had no direct contact with those sick, and one appears to have become infected after simply saying “hello” when they crossed paths.

“This is not close contact, and it is not prolonged contact,” said Joseph G. Allen, director of the Healthy Buildings Program at the Harvard TH Chan School of Public Health.

Studies so far suggest that the disease is most contagious when people are carrying a lot of virus, perhaps just as they start to feel sick. But there have also been too few eruptions large enough to say for sure.

“We have so little data that it’s really difficult to say anything concrete or definitive,” said Kartik Chandran, a virologist at the Albert Einstein College of Medicine.

Still, the fact that there have been very few cases should in itself reassure people that the virus is not very contagious, he and other experts said. After weeks of being together on the ship, only 11 of the approximately 150 passengers became infected, Dr. Tedros firmly. “You can see that the virus is actually not as effective as Covid,” he said.

One person in the Argentina outbreak became ill after sharing a hospital room with a hantavirus patient, but again had no physical contact.

Hantaviruses typically infect people when they inhale virus particles from rodent feces. According to some experts, this fact leaves open the possibility that human-to-human transmission could possibly also occur via the air.

“I don’t understand why we’re so reluctant to acknowledge the inhalation route when we talk about person-to-person transmission,” said Linsey Marr, an expert in airborne virus transport at Virginia Tech.

“Airborne transmission is certainly the simplest explanation in these cases,” she said of the Argentinians who had no direct contact with patients.

Dr. WHO’s Tedros said his organization did not refer to the findings about spread at birthday parties because they had not been replicated in other studies and because close contact is the most common way the virus spreads.

But Gustavo Palacios, a virologist at the Icahn School of Medicine at Mount Sinai and author of the article, disagreed with this stance.

“Our paper is important because it helps define the outer limit of what the Andean virus can do under favorable transmission conditions,” he said. “Most events will not look like this, but public health guidance must still take this possibility into account.”

In the United States, the CDC did not issue guidance or statements on the hantavirus outbreak until late Friday and did not hold a news conference until Saturday, nearly a month after the first passenger died. Transmission is still described as requiring close or intimate contact.

The CDC appears to have set an arbitrary measure of proximity and recognized the threshold as “not absolute.” Staying at a distance of less than 1.80 m for more than 15 minutes is listed as a risk warning outside of the Covid regulations.

Publicly, some U.S. health officials have shown that they do not clearly know the facts of the current outbreak. Speaking in the Fox News interview about the first two people to die from the virus, Dr. Bhattacharya incorrectly said the couple were in their 80s (they were 70 and 69) and added: “People who were very close to them, the housemates, a doctor who took care of them, they were the ones who showed symptoms.”

He was wrong about the details. CDC scientists were not on the ship to investigate the outbreak, but WHO officials who led the investigation are still investigating how other passengers became infected.

The third person who died, an 80-year-old German, was neither a roommate of the first two nor on the same deck. But she may have eaten with them or been to other places, Dr. Maria Van Kerkhove, the WHO’s director of epidemic and pandemic preparedness.

Andrew Nixon, a spokesman for the Department of Health and Human Services, which oversees the CDC, said federal authorities were “fully engaged from the start.”

He did not respond to questions about the science behind the six-foot guide or about Dr. Bhattacharya’s mistakes.

“Attempts to second-guess this response overlook the ongoing work being done to protect the health and well-being of American citizens,” he said.

The WHO does not include the 6-foot distance in its guidelines and acknowledges the scarcity of data, including on transmission, in its description of the outbreak.

“We are learning, and I think we will continue to learn for some time,” said Dr. Van Kerkhove. “The book is not written.”