Peter Jahrling, one of the country's top scientists, has dedicated his life to studying some of the most dangerous viruses on the planet. Twenty-five years ago, he cut his teeth on Lassa hemorrhagic fever, hunting for Ebola's viral cousin in Liberia. In 1989, he helped discover Reston, a new Ebola strain, in his Virginia lab.



Jahrling now serves as a chief scientist at the National Institute of Allergy and Infectious Diseases, where he runs the emerging viral pathogens section. He has been watching this Ebola epidemic with a mixture of horror, concern and scientific curiosity. And there's one thing he's found particularly worrisome: the mutations of the virus that are circulating now look to be more contagious than the ones that have turned up in the past.



When his team has run tests on patients in Liberia, they seem to carry a much higher "viral load." In other words, Ebola victims today have more of the virus in their blood — and that could make them more contagious.



We spoke last week about his work studying the disease, how this Ebola virus may be more dangerous than others, and what that means for the epidemic. What follows is a transcript of our conversation, lightly edited for clarity and length.



If you want to learn more about Ebola and this epidemic, read our cardstack.

Julia Belluz: What concerns you most about the virus circulating now?



Peter Jahrling: I want to know if this virus is intrinsically different from the one we have seen before, if it is a more virulent strain. We are using tests now that weren't using in the past, but there seems to be a belief that the virus load is higher in these patients [today] than what we have seen before. If true, that's a very different bug.



One of the studies we're going to do here is to test the virulence of this new strain in experimentally infected primates and compare it with the reference strain, and look at whether it is hotter, extrapolating from monkeys to people. It may be that the virus burns hotter and quicker [meaning it's more contagious and easily spread].

JB: Yet everyone is worried about Ebola going airborne...



PJ: You're seeing all these patients getting infected, so people think there must be aerosol spread. Certainly, it's very clear that people who are in close contact with patients are getting a very high incidence of disease and not all of that can be explained by preparation of bodies for burial and all the standard stuff. But if you are to assume that the differences in virus load detected in the blood are reflected by differences in virus load spread by body secretions, then maybe it's a simple quantitative difference. There's just more virus.

"viral loads are coming up very quickly and really high, higher than they are used to seeing."

JB: A higher viral load means this Ebola virus can spread faster and further?



PJ: Yes. I have a field team in Monrovia. They are running [tests]. They are telling me that viral loads are coming up very quickly and really high, higher than they are used to seeing. It turns out that in limited studies with the evacuated patients, they continued to express virus in blood and semen. What does that mean? Right now, we just don't know.

JB: Can you entertain the air-borne hypothesis. Do you think it's plausible?



PJ: You can argue that any time the virus replicates it's going to mutate. So there is a potential for the thing to acquire an aerogenic property but that would have to be a dramatic change. When scientists have done studies, playing with influenza strains to make them more virulent, when they increase the aerosol potential of a flu strain, they also reduce its virulence. So when you start messing with viruses, you usually make them less virulent.

JB: There have been worries that Ebola can become a pandemic like HIV and spread around the world. Even Tom Frieden, director of the Centers for Disease Control and Prevention, was recently saying as much. Your thoughts?



PJ: The mode of transmission is different between the two viruses. Ebola causes an acute infection which you either die from or you're immune, you don't carry the virus for long periods of time. Whereas with AIDS, a lot of people transmitting AIDS didn't know they have it. Before we had a triple cocktail therapy, AIDS was lethal with the exception of a few people who were not susceptible. Long term AIDS was hotter than Ebola. My gut feeling is that Ebola is going to burn out in human populations.



JB: Why are you optimistic about this epidemic burning out?



PJ: In this epidemic, it would appear that there have been multiple introductions [of the virus from animals to humans]. It's not all person to person transmission. It's coming from animals again and again. [This means people need to be near potential animal hosts — believed to be fruit bats endemic to Africa — to get the virus.] Now there are all these different strains. That could also mean the virus is more mutable. We can't yet say. I think it's unlikely that this thing is going to perpetuate in humans.