Amna Nawaz:

Three people are dead and nearly 150 quarantined on a cruise ship off the coast of West Africa. The World Health Organization is investigating an outbreak of the rare, but deadly hantavirus on board.

William Brangham has more.

William Brangham:

Amna, there is no cure or FDA-approved vaccine for hantavirus, which is normally spread by contact with infected rodents. But the WHO said today they believe there's evidence of a rare instance of human-to-human transmission on that ship.

The agency has identified two confirmed and five suspected cases, including the three deaths. One man is now in critical condition in an ICU in South Africa. The WHO says the risk to the public remains low.

But for more on this outbreak, we are joined again by Dr. Celine Gounder. She is editor at large for public health at KFF Health News and an infectious disease specialist and epidemiologist.

Dr. Gounder, nice to have you back on the program.

Before we get to this particular outbreak, just tell us a little bit about what is hantavirus and how do humans normally get infected by it?

Dr. Celine Gounder, KFF Health News:

William, hantavirus is in fact a family of viruses that are carried by rodents.

So people typically get infected by breathing in dust that has been contaminated with mouse or rat droppings, urine or saliva. And most infections are happening when somebody disturbs a rodent contaminated-space. So it might be cleaning out a shed or sweeping in the basement, opening a building that's been closed for a while.

In the U.S., the severe form is called hantavirus cardiopulmonary syndrome, so cardio, the heart, pulmonary the lungs. It starts with fever, headache and muscle aches, but then can rapidly progress to severe breathing problems and shock.

And then, depending on exactly which hantavirus between 12 and 45 percent of people who develop that severe form go on to die. But I think it's really important to emphasize that this is exceedingly rare. In the United States, we have had less than 900 cases over the past 30 years.

And, globally, there are an estimated 200,000 to 300,000 infections a year, most of which are milder forms seen in Europe and Asia.

William Brangham:

So what do we know about this outbreak on the ship? And how concerning should it be that the WHO seems to believe that there is human-to-human transmission of the virus?

Dr. Celine Gounder:

So this is a ship that departed from Ushuaia in Argentina on April 1 and sailed through Antarctica and up the coast of Africa.

As of today, seven people have been affected, three passengers have died, and two cases have been confirmed to be hantavirus by lab tests, including one of the passengers who has died. As you mentioned earlier, there is one person who's in intensive care in South Africa. They are in critical, but stable condition.

And there have been at least an additional person who is reporting a mild fever now. The WHO and South African authorities and others have been working on investigating these cases, taking samples from patients. But, for now, the passengers remain aboard the ship, the remaining passengers, to be quarantined until the situation can be thoroughly investigated.

William Brangham:

Let's say that the WHO does confirm a human-to-human transmission. Does that -- I know that can be rare. It does happen with hantavirus. But would that potentially indicate that this virus is shifting or mutating in some way?

Dr. Celine Gounder:

So, we know that there is one form of hantavirus, Andes virus, which circulates in Argentina and Chile that has been documented to spread person to person. No other hantavirus does this, but this one does. We have evidence going back to the late '90s showing evidence of person-to-person transmission.

So it's quite rare, but, with this particular form of hantavirus, it is possible. But I do think it's important that people understand that this still requires very close, prolonged contact. It's very different still from viruses that can become pandemics, like COVID or flu, which can be transmitted much more easily through the airborne respiratory route.

William Brangham:

All right, that is Dr. Celine Gounder at KFF News.

Thank you so much, as always, for being here.

Dr. Celine Gounder:

My pleasure.