SACHA PFEIFFER, HOST:
Public health experts are working to contain the hantavirus outbreak now that passengers have disembarked from the cruise ship where it started. The risk to the general public is very low, according to many of those same experts. They're pointing to one past outbreak for clues about how this virus behaves, as NPR's Gabrielle Emanuel reports.
GABRIELLE EMANUEL, BYLINE: In recent days, Marty Cetron has been poring over a study published several years ago in the New England Journal of Medicine. Cetron spent 20 years heading the Division of Global Migration and Quarantine at the Centers for Disease Control and Prevention.
MARTY CETRON: There's four figures that I'm looking at here.
EMANUEL: The paper he's studying - it delves into a hantavirus outbreak in Argentina from 2018 to 2019.
CETRON: They did an excellent job, and as a result of that, we are much wiser.
EMANUEL: Wiser about how the cruise ship outbreak might unfold. In Argentina, basically, one man got hantavirus, presumably from the most common mode of transmission - breathing in virus particles from an infected rodent's urine, feces or saliva. But then what happened is it started spreading, eventually to 33 other people, 11 of whom died. That fatality rate, with about a third of people dying, is, so far, the same as today's outbreak. The World Health Organization says the virus spreads in close, prolonged contact. Cetron says what that looks like can be seen in this Argentine outbreak. Scientists can't say for sure if it's in the air or the virus lives on surfaces, but it did spread human to human in social settings - at a funeral...
CETRON: And a birthday party.
EMANUEL: With those who got sick, sitting relatively near someone who was already unwell.
CETRON: But what's notable is that the vast majority of those 34 cases were dead-end infections. They didn't spread to anyone else.
EMANUEL: But some people spread it to multiple other people. The study calculated just how infectious this virus is. Scott Weaver is with the University of Texas Medical Branch.
SCOTT WEAVER: So if a person becomes infected with this hantavirus and there are no control measures in place, they're going to transmit, on average, to two other people. And that was determined from that Argentina outbreak.
EMANUEL: This number - two - puts hantavirus on the low end of infectiousness. But it's still high enough, Weaver says, that passengers on the ship and people who they've been in contact with need to be monitored and take precautions if they do get sick.
WEAVER: By isolating people and using personal protective equipment.
EMANUEL: He's confident that with the right control measures in place, today's hantavirus outbreak can be contained.
Ronald Nahass, president of the Infectious Diseases Society of America, says the Argentine case holds yet another promising clue for him.
RONALD NAHASS: They were able to look at the genetic sequences of the virus from that particular outbreak and compare it to an earlier outbreak from 22 years earlier. There was almost no genetic divergence, which is really extraordinary.
EMANUEL: That stands in stark contrast to the flu and COVID, which we now know mutate regularly and require updated vaccines. For hantavirus...
NAHASS: You wouldn't expect a lot of change in the character of the illness or the degree of transmissibility.
EMANUEL: Now, things could change. Anything is possible when dealing with infectious diseases. But so far, Nahass says this relatively low infectiousness and lack of mutations bodes well for stopping this outbreak. Gabrielle Emanuel, NPR News.
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