Carl Zimmer Explores The Weird Lives Of Viruses

In his book A Planet of Viruses, science writer Carl Zimmer catalogs a menagerie of viruses, from the bacteriophages that prey on ocean-dwelling microbes to those which infect humans, such as smallpox, HIV and the papillomaviruses behind cervical cancer and the common wart.


You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

Got a little bit of astounding trivia for you tonight. It's a Friday night. You want to really knock the socks off some people you're talking to, you know? I'm going to give you a little quiz first. What has a tiny shell, it's invisible to the naked eye, it affects the Earth's climate and causes cancer? It's a virus.

They've learned to live pretty much anywhere in the world and to use nearly any living thing for a host. And here is the astounding statistic: Viruses kill half the bacteria in the ocean every day. Every day, viruses kill half the bacteria in the ocean. And they invade a microbe host 10 trillion times a second around the world. Wow.

But are the viruses alive themselves? How do you - how did they get there? How did they get here? And now that so many bacteria are developing resistances to antibiotics, is it time to unleash viruses on them?

Just a few of the many mind-boggling facts and questions about viruses in my next guest's book, "A Planet of Viruses." Carl Zimmer is the author. He writes regularly for The New York Times and is a contributing editor at Discover. He's here in our New York studios.


Mr. CARL ZIMMER (Author, "A Planet of Viruses"; Contributing Writer, The New York Times): Hi, Ira. Thanks for having me.

FLATOW: Are these just astounding to me or did you - when you did your research for this book - these are just amazing.

Mr. ZIMMER: Yeah. Yeah. I just had to keep going over and over it again, because I would look up, for example, how many viruses there on earth. And the number I get is, I keep finding, is 10 to the 31st power. That's one with 31 zeroes after it, which is 10 billion trillion, trillion. That's more stars than are in the universe. If you had a lot of spare time and you want to stack all those viruses end to end, they would go about 100 million light years.

FLATOW: I can't believe it.

Mr. ZIMMER: Neither can I, but that's...

FLATOW: I can't believe it.

Mr. ZIMMER: ...that's just how it is.

FLATOW: And there - and tell me about the oceans. They eat half the bacteria in the oceans every day?

Mr. ZIMMER: Yeah. It's funny. There used to be a time when people thought the oceans are pretty much virus-free. But now we realize that there might be, say, maybe a billion viruses in every teaspoon of water. And they're attacking the bacteria. There's lots of bacteria in the ocean. And so they will just do a slaughter of these bacteria every day. Of course, the bacteria grow back pretty fast, but still it's a tremendous thing because all those bacteria contain carbon and lots of nutrients. And so they're constantly cycling all this to the ocean and into the atmosphere.

FLATOW: Wow. 1-800-989-8255, talking with Carl Zimmer, author of "A Planet of Viruses." You can tweet us @scifri.

You know, when you said that there are 10 to the 31 viruses...

Mr. ZIMMER: Mm-hmm.

FLATOW: ...then it seems almost incredible that our body is fighting off so many viruses every day. It must be being attacked all the time by viruses. And we're fighting them off if they're everywhere, right?

Mr. ZIMMER: Well, they're also inside of us.


Mr. ZIMMER: So you look pretty healthy today. There are probably about -from the latest estimates I saw - about four trillion viruses inside of you right now. And they're not making you sick, because they're infecting all the bacteria that live inside of you.

FLATOW: So they're holding off the bacteria from attacking me, also, possibly.

Mr. ZIMMER: Right. Or they might actually be helping the bacteria. They might be balancing the ecosystem in there so that some species do well and others don't.

FLATOW: Now these bacteria that are all over the ocean and killing half - the viruses that are killing half the bacteria, how does that affect the ecosystem if you've got all these dead bacteria raining down in the ocean all the time?

Mr. ZIMMER: That's right. So you got a lot more carbon that's freed up and moving around. And there's actually a big question about where exactly that carbon goes. Do the bacteria there just suck it back up again, or does it rain back down? What would the world be like without all these viruses?

One pretty dramatic idea is that, actually, you know, all that carbon that's coming out and then getting sucked back up could be affecting the Earth's climate because any of that carbon that gets back up in the atmosphere is going to be trapping heat. So, you know, the temperature we're at is partly set by viruses.

FLATOW: Mm-hmm. Let's talk about one of my favorite topics I've been talking about over the years. And you have a chapter in your book about bacteriophages, viruses that eat, attack bacteria. And this was first discovered when?

Mr. ZIMMER: This was first discovered in World War I. So people knew a bit about viruses before then for about 30 years, but they had found them in people, in animals and in plants.

But then a doctor, a Canadian doctor named Felix d'Herelle discovered that there were viruses that could wipe out bacteria. He would treat a dish of bacteria with fluid that he had filtered out from - actually from patients who are sick with dysentery. And he found that he could just kill these bacteria. And, eventually, what he concluded was that these were viruses that were attacking them.

And it was a pretty radical idea at the time. People didn't believe him. Nobel Prize winners were going after him. But he held to it. He actually became the hero - fictionalized hero in a novel called "Arrowsmith," made a movie out of it. And he actually did quite well. He actually started a whole business of using these viruses to treat bacterial infections. In France, you could go out and buy these things.

FLATOW: And so there were viruses that could - that are - that exist in nature that could kill the worst bacterial infections, the bacteria that cause these infections we know. MRSA, all these things, there are natural occurring viruses that could kill them.

Mr. ZIMMER: Yeah. Every species of bacteria has a bunch of different species of phages that can kill it. That's just evolution. It's been going on for billions of years. And you can just go out, I mean, every time scientists go out, they'll find a new phage for attacking a particular species of bacteria.

FLATOW: So why aren't they sitting in our medicine cabinet? Or are the doctors giving us injections of these things?

Mr. ZIMMER: It's a strange, wonderful, historical fluke. Basically, what happened was in the 1930s, scientists started to discover antibiotics. And here were chemicals, they were reliable, they knew how to make them, and everyone said, oh, these are the silver bullet. And so phage therapy disappeared, except for the Soviet Union.

Everywhere else, everyone switched over to antibiotics. And that was -we've had a pretty good run with antibiotics, but now it's not looking so good, because we're getting bacteria that are resistant to them, as you said.

FLATOW: And so why don't we have FDA approval of some of these things?

Mr. ZIMMER: You know, the FDA has a lot of - the FDA's kind of sluggish.

(Soundbite of laughter)

Mr. ZIMMER: And...

FLATOW: That's diplomatic.

Mr. ZIMMER: Yeah.

(Soundbite of laughter)

Mr. ZIMMER: And if you go to them and say, hi, I've got a virus, and I want to go infect patients with it because it'll kill bacteria, it's kind of hard to get them to sign off on. In fact, they're not even sure how to approve it, ironically.

And so, there's a lot of research going on right now, here in the United States, to develop them. They're just starting to crack that barrier. So now there are actually food sprays where you - companies can spray phages on their food to stop food poisoning.

FLATOW: So, there might be some hope, because I've been talking about this for decades with other scientists that say this is just silly, basically.

Mr. ZIMMER: Yeah. It gets sillier all the time, because we're getting better at selecting the right phage for the job, you know? You can create, what they call, libraries of these viruses, and you could imagine them being in a hospital. So you come in with an infection, and they take a sample, and then they go check out their library of phages and see which one will do the best job. And then they send them after your bacteria.

FLATOW: And the almost magical thing to me is even as the bacteria mutates to become resistant to that virus, you'll get another virus that mutated with it, or knows how to attack that bacteria.

Mr. ZIMMER: That's right. Antibiotics can't evolve. Viruses can. And not only that, but we know how to engineer them now, so you can actually insert genes to make them more effective.

FLATOW: I'm just - you know, some things are just so illogical.

Mr. ZIMMER: Yeah. Maybe in 10 years.

(Soundbite of laughter)

FLATOW: The kinds of - 10 years from now. 1-800-989-8255. At least it's not 30.

Let's go to John in Bethesda. Hi, John.

JOHN (Caller): Hello. Good afternoon.

FLATOW: Hi, there.

JOHN: So my question is - I use United Streaming in my classes, and they have a video on viruses. And in this particular - or this video, it says that viruses are the oldest form of - and I think they use life loosely. But if viruses require a living host, how could they be the oldest living thing on Earth?

Mr. ZIMMER: Well, you know, it could be what they're saying there is that their hosts are long since gone and they're still around. There are actually some viruses that are weirdly primitive. So, for example, plants can get infected with things that are called viroids. They don't even have a protein shell. They're just naked genes that can infect plants, and they're tiny, tiny little things.

JOHN: Are these like prions in humans?

Mr. ZIMMER: Well, no, because they're actually made out of a single strand of DNA - RNA. So prions are proteins. These are viruses. They're made of RNA.


Mr. ZIMMER: But these or something like them could be just relics of the earliest stages of life, back when maybe there weren't even any cells. You have to just think of kind of a soup of genes, and maybe some genes were good at parasitizing others and getting them to make copies of themselves.

JOHN: And then would there be a possibility if these bacteria phages mutating to become pathogenic to humans if you use them on the bacteria?

Mr. ZIMMER: No, because, you know, bacterial biology and human biology are profoundly different. And, so, you know, it, you know, these phages are specific just for one species of bacteria. But, you know, we share a common a ancestry with bacteria that lived, I don't know, maybe three-and-a-half, four billion years ago. So you - and, you know, you have phages with you right now in your body when you're perfectly healthy. Every time you have yogurt or eat pickles, you're eating phages. So you don't have anything to worry about with them.

FLATOW: Going to have some (unintelligible) yogurt and pickles today. We're talking with Carl Zimmer, author of "A Planet of Viruses," a really interesting book. And it's a quick read. It's chockfull of all kinds of interesting facts. For example, there's a chapter in your book that deals with retrovirus DNA in our own genome. How do we get viruses in our genome?

Mr. ZIMMER: Well, they're everywhere.

(Soundbite of laughter)

Mr. ZIMMER: Well, retroviruses - we're most familiar with HIV. That's a retrovirus. And what - the way the retroviruses reproduce is they actually take their genetic material and insert it into our own chromosomes. And then our chromosomes then make new viruses. Every now and then, on very rare occasions, a retrovirus will end up in, say, a sperm cell or an egg and insert its genes there. And then suddenly, if that sperm or egg become - gives rise to a new organism, a new animal, a new person, every cell in that body has got that virus.

And it turns out that over tens, hundreds and millions years, our ancestors have been picking up viruses like this, and they've been clogging our genomes. So now they are probably about 100,000 elements in the human genome that you can trace to a virus ancestor. It makes up about 8 percent, all told, of our genome. Just bear in mind that all of the genes that encode proteins only make up 1.2 percent of our genome. So we're much more virus than human, really.

FLATOW: This is SCIENCE FRIDAY, from NPR. I'm Ira Flatow, talking with Carl Zimmer, author of "A Planet of Viruses," learning that we're more virus than human in our genome. Wow.

1-800-989-8255. Let's see - some interesting calls coming in.

Nathan in Denver. Hi, Nathan.

NATHAN (Caller): Hello. Thanks for taking my call.

FLATOW: Hi, there.

NATHAN: Hey. I have a biochemist friend that recently told me that he's under the impression that climate change could potentially have a big effect on releasing viruses - maybe in frozen soils, I don't know all the details - that we've never been exposed to or never encountered. Can you talk a little bit about how climate change is going to affect the world of viruses?

Mr. ZIMMER: Well, I doubt that it's going to be unleashing viruses from the soil to make us sick. I mean, viruses are pretty delicate things. However, it could mean that insects that carry viruses could move into new territories and start making people sick with things like dengue fever, for example. And so those kind of shifts are things that we need to worry about. I mean, we also need to be concerned just about viruses hopping from one species to another.

So SARS, you may recall, came from bats, actually. And through animal markets in China and things like that, they were able to get into our species. And fortunately, in the case of SARS, we seemed to have beaten that thing down. But in the case of HIV, that was a chimpanzee virus that got into humans several times, and with horrible consequences.

FLATOW: Hmm. So we should be saying that just like we - there's a phrase, oh, there's an app for that, if you have a bacteria, oh, there's a virus for that.

Mr. ZIMMER: There's a virus for everything.

FLATOW: To conquer MRSA, you could - there's a virus that could conquer MRSA or these other...

Mr. ZIMMER: Potentially. Potentially, yeah.

FLATOW: And we could genetically engineer one.

Mr. ZIMMER: That's right. I mean...

FLATOW: If we had to.

Mr. ZIMMER: Yeah. You can add in new genes. So, for example, there are viruses that have been engineered with extra enzymes to actually break up biofilms. So bacteria protect themselves by forming these gooey carpets. And so scientists at MIT have engineered viruses that can just blast that biofilm away.

FLATOW: In the minute or two we have left, let's talk about papillomavirus. You have a story in your book on how scientists were studying rabbits with horn-like warts on their heads, a sort of jackalope kind.

Mr. ZIMMER: Yeah...

FLATOW: I think we have on our website, a picture of that. It's just amazing.

Mr. ZIMMER: Yeah. Well, if you ever go out West, you see pictures, postcards of jackalopes, which are just rabbits with little prong or antlers stuck on them. But, in fact, rabbits do sometimes form these horn-like things on their heads, and it's caused by papillomaviruses which get into their skin and actually sort of speed up the growth of the skin cells. And it was through - partly through the discovery of these, quote, unquote, "jackalopes" that scientists discovered that viruses can be an important cause of cancer. Fifteen percent of all human cancers are caused by viruses, and the papillomavirus causes cervical cancer.

FLATOW: Is there anything about viruses you don't know...

(Soundbite of Laughter)

FLATOW: ...that you want to more of, or you think we should know more about? Are there questions that still remain about viruses?

Mr. ZIMMER: Yes. Because I'm sure that the more that scientists explore extreme places, the weirder the viruses are that they're going to discover. I mean, they've even discovered now viruses that infect other viruses. So there's no telling what they're going to be finding out next.

FLATOW: And they could - and they would be living in even the hostile areas, deep in those thermal vents, things all over the oceans.

Mr. ZIMMER: Yeah. Oh, well, like, I write on the book about a cave, about a mile underground with these gigantic, 60-foot long gypsum crystals. It's a bizarre place. And there's a little bit of water in there, and - which has some bacteria in it, and those have viruses in them. So anywhere that there is life, you're going to find viruses -maybe even on other planets.

FLATOW: Can't think of a better place to end than at that thought. Thank you very much, Carl, for coming in.

It's a great book, Carl Zimmer's book: "A Planet of Viruses." Terrific. If you want to learn all these great facts about viruses, it's a great read. Carl Zimmer is the author of that book, and he's a regular writer for The New York Times and a contributing editor at Discover.

Thanks again.

Mr. ZIMMER: Thank you.

FLATOW: Have a good weekend.

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