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TERRY GROSS, host:

This is FRESH AIR. I'm Terry Gross.

It's another big summer for seductive vampires in movies, books and television; but the creatures that really suck our blood are creatures with zero sex appeal: mosquitoes.

In the U.S., mosquito bites are usually no worse than a distracting itch, but in many parts of the world mosquitoes are very dangerous. They carry malaria, a disease that's been with us for half a million years and kills about a million people each year.

How mosquitoes bite and infect humans and animals and why malaria has been so hard to eradicate in spite of the drugs we have, are among the subjects Sonia Shah writes about in her new book "The Fever." She was first exposed to and terrified by malaria-bearing mosquitoes when she was a child visiting her grandparents in India.

Sonia Shah, welcome to FRESH AIR. Now, maybe other people know this, but I didn't know this until I read your book. It's not the mosquito itself that actually is responsible for the malaria, it's a parasite that the mosquito carries that actually spreads the poison, so to speak. Would you tell us about this parasite?

Ms. SONIA SHAH (Author, "The Fever: How Malaria Has Ruled Humankind for 500,000 Years"): Well, the parasite is called plasmodium, and it's protozoan. It's a very wily little creature.

It reproduces sexually and asexually, but all of this takes place inside the bodies of mosquitoes for half their life, and then the other half of the life in whatever host they are targeting; and different malaria species target different hosts.

So for us, there's at least five malaria parasite species, these species of plasmodium that actually infect humankind, and what they do is they come into our bodies in the saliva of a mosquito, they hide in our liver for a while, but what they're really after is the hemoglobin in our red blood cells. So that's what they feast upon. And then they leave to go on and infect another person.

So it's this cycle of being infected by malaria parasites and having them feed on our red blood cells, the hemoglobin in our red blood cells, that makes us sick from malaria.

GROSS: Wait until they leave? How do they leave your body after they've infected you?

Ms. SHAH: Well, they go through several cycles of regeneration inside the human body, and so they sort of go inside the red blood cells, and they chomp down all the hemoglobin and reproduce inside of there.

Once they're done, they burst out, and that's actually when you start feeling sick. And they do that for several cycles. Meanwhile, some of them transform into what are called gametocytes, and these are the form of the parasite that then comes out into the bloodstream and waits for another mosquito to come along and bite that infect person and carry and then they do another cycle of reproduction inside the mosquito and then go on to the next victim of the mosquito.

GROSS: Wow, that's really horrible. So as you're suffering, you're also becoming a breeder.

Ms. SHAH: Exactly, and you dont really know about that. I mean, I think that's one of the great tricks of this parasite, is that you can be infected for a week without really realizing that you've infective.

So you don't feel sick the whole time you have malaria. You have the fever and chills that are the typical symptoms of malaria only occur when those parasites burst out of your red blood cells. What that does is release some of the poisons from their digestive process, and that is what, you know, you have this sort of toxic effect in the body, and that's what makes you sick.

But meanwhile, the parasite has already, you know, doubled, tripled, has you know, its numbers have become huge inside the body, and they're already creating these gametocytes that get picked up by other mosquitoes.

GROSS: So what makes a mosquito a good host for this horrible parasite that causes malaria?

Ms. SHAH: Well, mosquitoes and the parasite probably, sort of, evolved together. So the parasite itself has some vestigial machinery inside of it that suggests that it once photosynthesized.

So it was probably some kind of, like, algae floating in the water. And so the larvae are formed inside - in bodies of water. So they probably were together for a lot longer than the parasites started infecting us, but I mean, mosquitoes take these blood meals.

As we all know, the itchy bites that we get are from the female mosquito trying to suck our blood, and the reason they are taking blood is, not for food for themselves, but to nourish their eggs.

So that's, like, evolutionarily speaking, such a hugely important thing to do, you know, to secure the next generation. So the mosquito actually will risk her life to get a few drops of blood to feed her eggs, because, of course, taking that blood meal for a tiny little mosquito is incredibly dangerous.

I mean, not only can they be easily swatted away and killed by the animals that they take blood from, but once they take the blood...

GROSS: Like you and me.

(Soundbite of laughter)

Ms. SHAH: Well, exactly. They can they get filled up with such a huge volume of blood that they can't fly, or they can't fly very well, and that is a mortal debility for a mosquito, obviously. It needs to be able to fly to avoid predators and things.

So it risks its life to do that. So that makes the parasite's exploitation of this behavior in the mosquito so wily, because the mosquito is not going to give up its blood meal. I mean, it's more important than food. It's about reproduction.

GROSS: So the parasite has a pretty confirmed ride.

Ms. SHAH: Exactly, so long as the mosquitoes are biting. But the trouble is, mosquitoes are very vulnerable to the environment. I mean, they're cold-blooded, obviously, and they require bodies of water that are pretty ephemeral.

I mean, a lot of times mosquitoes are breeding in puddles, which can dry up. They also breed on the edges of streams or ponds and things like that. And if that water gets flushed out by rains, or if the water becomes deeper because other water is coming into it, and fish can come and eat those mosquitoes.

So mosquitoes are, you know, they're reliable carriers in the sense that they're always going to try their best to get that blood meal and deposit parasites in that blood meal, actually in the saliva that they drop into the wound when they plunge their proboscis into your skin.

It's still something that is very vulnerable to the climate and to the local geography.

GROSS: Are there malarial mosquitoes in the U.S. today?

Ms. SHAH: There are many species of malarial mosquitoes in the U.S. today. So there's nothing environmentally...

GROSS: Do I want to hear more, or should we just end the interview now?

(Soundbite of laughter)

Ms. SHAH: I mean, it's amazing, really, because environmentally speaking, there's no reason for us not to have malaria again today. I mean, we once had malaria all over this country, particularly in the South, but right up through the Upper Mississippi Valley.

Michigan was considered, you know, the land of ills. It was known for its chills and fever. You know, people thought at one time that the West would never be settled because there was so much malaria in the Upper Mississippi Valley.

GROSS: And how come there isn't that much now?

Ms. SHAH: Well, there's been a number of changes. It happened pretty slowly. I mean, the sort of myth is that we developed DDT after World War II, and we blitzed millions of homes with DDT, which we did, and that ended malaria.

But actually, malaria was already very much on the decline by the time DDT came online, and it had to do with agricultural changes demographic changes, changes in settlement patterns.

You know, we drained a lot of our wetlands, and, you know, today we've lost probably half of the wetlands we originally had in this country. And as we did that, of course, we destroyed a lot of mosquito habitat.

We also paved over a lot of mosquito habitat, and then we also stopped living near wetlands and the shores of rivers because we stopped relying on those water bodies for our trade and our transportation.

You know, we started using railroads and then roads, and so we didn't have to live so close to water bodies that made us vulnerable to mosquitoes.

And we also improved our housing. I mean, I think that's a huge part of our solution to our malaria problem here in the United States, is we started screening our windows and screening our doors and, you know, having air conditioning and living indoors more.

GROSS: So what are my chances of getting malaria now?

Ms. SHAH: Here in Philadelphia? Probably pretty slim, unless the idea is that malaria could come back to the United States, but only if our public health system really fails.

So, you know, if you got malaria I mean, you could get malaria because malarial mosquitoes probably bite you when you're outdoors, when you have your windows open. They're around. They are biting you. And there is enough people coming over from malarious(ph) areas who carry parasites in their bodies that come into the United States.

I mean, a thousand or so, Americans get sick with malaria every year in the United States. So, it's not that the parasites aren't here, it's that when you get sick - if you got that sick you would spike a 103-104 fever, and you would run to the hospital right away and get prompt care.

And, of course, we have, you know, we have treatments that work for malaria, and we've had them for hundreds of years. So it's not that we don't know how to cure the disease.

GROSS: If you're just joining us, my guest is journalist Sonia Shah. She's the author of the new book "The Fever: How Malaria Has Ruled Humankind for 500,000 Years." Sonia, let's take a short break here, and then we'll talk some more about malaria and the parasite and the mosquitoes that spread it. This is FRESH AIR.

(Soundbite of music)

GROSS: My guest is Sonia Shah. She's the author of the new book "The Fever: How Malaria Has Ruled Humankind for 500,000 Years."

There was a period when there was an attempt to eradicate malaria by spraying with DDT, the very powerful, toxic insecticide which, you know, killed insects but also ended up being toxic to humans. Tell us first what the approach was in using the DDT.

Ms. SHAH: Well, it was a pretty good plan. After mosquitoes feed on people, so they're full of blood, they need to rest almost immediately because they can't fly very well.

So they rest on the nearest vertical surface that they can find, and they excrete out all of the liquid from the blood, and that makes them lighter so that they are able to fly away. So and that takes about 45 minutes.

So the idea with DDT was to spray the insides of houses, so spray all the walls of the interior of houses with a thin layer of DDT so that when, after mosquitoes took their blood meal, they'd land on this and for 45 minutes absorb all of this DDT, and that would kill them.

And so in the 1950s, the U.S. State Department actually decided that they would bankroll - they would suggest bankrolling a massive DDT blitz. This would be a global effort that would actually attempt to eradicate malaria forever. And that was the first time that we, as a species, had kind of risen up against this pathogen that had, you know, plagued us for millennia.

And about 93 different countries signed on to that effort. You know, about 18 countries out of that effort actually did succeed in eradicating malaria from their borders, and most of those were islands, where, you know, re-infection from other people coming in could be more easily controlled.

So many other countries, you know, they got a lot of DDT, and malaria did decline for some time, but since it wasn't a perfect effort, the mosquitoes learned how to circumvent DDT. So the DDT stopped working as well.

And meanwhile, people were losing their immunities to the disease. So there were a few years when many people in these countries under the DDT blitz stopped having exposure to malaria, but then as the DDT campaign fell apart, malaria came back, sort of with a vengeance. And there was a massive resurgence of malaria after the DDT campaign ended in the 1960s.

GROSS: So what do scientists think are the best approaches, now, to dealing with malarial-carrying mosquitoes?

Ms. SHAH: Well, we're still doing some of the same things we did in the 1950s. I mean, we're still spraying the insides of houses with different chemicals now. We're not using DDT so much, since that chemical has really fallen out of favor, although it still could be useful in some places.

So we're using sprays, and we're also using bed nets that are impregnated with insecticides, so that when mosquitoes try to reach somebody who is sleeping under a bed net, they actually absorb insecticide through the net, through their legs, actually, as they land on it.

GROSS: The mosquitoes absorb it through their legs?

Ms. SHAH: Yes, that's right, not the people inside.

GROSS: Okay.

Ms. SHAH: So the mosquitoes will come buzzing towards the person who's sleeping inside, and as they do, they'll land on the net. And by landing on the net, they'll absorb, you know, a killing dose of the insecticide on the net.

GROSS: Now, you write that the new global movement against malaria is led by private interests. What kind of private interests?

Ms. SHAH: It's really a coalition of different actors. I mean, the WHO is part of the global campaign against malaria today, but it's really not the leader anymore.

The Gates Foundation, for example, has become really the leader in setting the global health agenda, because they're just such a huge, you know, a huge contributor to a lot of these programs.

So it's private philanthropists, it's WHO and organizations like the Global Fund to Fight TB, Malaria and Tuberculosis. And then a number of NGOs and state actors and also corporations. I mean, companies have really stepped up their interest and their stake in fighting malaria, particularly in Africa.

GROSS: Yeah, well, you write oil companies have become active in the anti-malaria campaign because of their oil interests in Africa.

Ms. SHAH: I mean, it's oil companies and mining companies that are really in terms of the corporate participation in the anti-malaria fight, it's probably the mining and oil companies that are really the biggest actors, because they are dealing with it, you know, just in their own businesses, because, of course, oil companies are doing a lot of work in West Africa now, and they've had to deal with awful malaria problems, just in their own installations.

I remember visiting - seeing Bioko Island off the coast of Equatorial Guinea, and Exxon Mobil had built all of these ranch houses there for, you know, the natural gas installation they had put up there. They built all these ranch houses because they wanted all these Texas oil workers to come live there and work on it.

Well, nobody came. They were all empty because people were scared of coming, because of the malaria.

GROSS: So we have ways of preventing and treating malaria? What are the ways?

Ms. SHAH: Well, we know that by avoiding the bites of infected mosquitoes, we can avoid completely getting infected with malaria. So the trick is knowing where those mosquitoes are living and, you know, building our habitations far away enough that they don't bite us, and also protecting ourselves during the times when they bite.

So these are things that entomologists have figured out in many places. You know, in some places, the malarial mosquitoes hatch from salty waters. In some places, they prefer freshwater that's sunny. Some places, they prefer streams and dark, you know, shaded waters. But these are things that can be known.

And we can also know when the mosquitoes are biting. Oftentimes, they bite in the middle of the night. Some of them also bite in the evening. So we can know when to avoid the bites of mosquitoes.

We also can know - to recognize the symptoms of malaria and get prompt treatments, because the treatments we have, the medicines we have, actually kill the parasites in our bodies so that we're not infective anymore.

So if we get prompt treatment, that also can also start to end malaria. And of course, that is what we have done here in the United States because we had malaria all of this country, and, you know, prompt treatment and changing the way we live actually has protected us.

GROSS: Sonia, you have an interesting and kind of scary history with mosquitoes. You grew up in New England, but your grandparents were in India when you were a child, and you used to visit them every summer. And the mosquitoes were a real problem. Were you dealing with malarial mosquitoes when you visited your grandparents in India?

Ms. SHAH: Almost certainly I was. I didn't know it at the time, but, you know, malaria was always this thing that everyone else in India was allowed to have, and I wasn't allowed to have. So as a kid...

GROSS: What do you mean by that?

Ms. SHAH: Well, it had a kind of romance to it. I mean, my cousins I was the American kid. You know, I was the American-Indian kid who went back, stayed with all my Indian cousins, and I really wanted to fit in.

And of course, they were allowed to, you know, sleep under the stars and sleep under the ceiling fan, but I had to be enclosed in this, like, hot, suffocating mosquito net. It would take about 20 minutes to put it up, and, you know, I just wanted to be like them.

But I had to be protected from the bites of mosquitoes, and I had to take these giant horse pills that were, you know, the prophylactic medications for malaria at that time, whereas they were allowed to have their bouts of malaria, you know, and it was just something they lived with.

I mean, they considered it a normal part of life, but for me, it was very dangerous. So it was another way that I was sticking out, and the mosquitoes seemed to know it because they really, I mean, they just attacked me and my sister.

They somehow knew that we were not locals, or somehow we responded in this, you know, in this very virulent way. We'd be covered with scabs while all my cousins would just be completely smooth and, you know, unbothered by the mosquitoes.

GROSS: So what does it say that you've devoted a considerable amount of time to studying malarial mosquitoes?

Ms. SHAH: Well, I think I have kind of a I mean, most people would just have sort of a hate relationship with malarial mosquitoes, but I kind of have a love-hate relationship because it is something I've been so fascinated by and yet repelled.

I mean, and this goes back to, you know, mosquitoes and my own family's response to insects generally. We come from the Jain religion, and, you know, most people if they hate mosquitoes can swat them without guilt, but I can't.

I mean, to this day, I feel guilty if I kill a mosquito because in the Jain religion, you're not supposed to I mean, you're not even supposed to walk on grass because that could kill the little, you know, ants and microbes that are in the grass.

So, you know, my grandmother used to praise people who let flies just walk all over them because they were so nonviolent, you know, and they'd or praise people who would take a spoonful of sugar and feed anthills.

So there was this whole ethos of being kind and nonviolent, even to insects, I mean to all creatures but even insects - whereas, you know, all I wanted to do was swat these mosquitoes. And of course, I did, and then I'd feel really guilty.

GROSS: Now, there's one more thing I want to ask you about. You mentioned that after a mosquito feeds, it's kind of too heavy to fly well. So it sits on a vertical surface, like a wall, for about 45 minutes and does what?

Ms. SHAH: It excretes out all the liquid from the blood. So it's just keeping the sort of proteins in the blood, and that's what it needs to nourish the eggs. So it's much lighter then because it's not, you know, they've gotten rid of all the excess water.

GROSS: Does it leave a stain on your wall when the mosquito excretes the liquids?

Ms. SHAH: You can actually see them doing this. It comes out as a clear liquid. So it looks like their urinating, basically, but you can actually see that liquid coming out. I've seen it myself.

If you take the time to actually a watch a mosquito that has bitten you sit on, you know, wherever it has flown to rest, you can actually see this happening.

GROSS: Is that a good time to kill a mosquito because it's heavy with blood, and it has to rest for a while, it's like a time out for the mosquito?

Ms. SHAH: Absolutely, and they can't fly very well at that time, either. So, I mean, I remember traveling in malarious places, the walls are always speckled with smooshed mosquitoes, because it's just so easy to kill them when they're resting on the walls, and also you can see them better.

GROSS: Of course, at that point, they've probably already bitten you, right?

Ms. SHAH: That's true. They probably have already bitten you or, you know, whoever else is in your house with you.

GROSS: Right, okay. Sonia Shah, thank you so much for sharing some of what you've learned about malaria. I appreciate it very much.

Ms. SHAH: Thank you.

GROSS: Sonia Shah is the author of "The Fever: How Malaria Has Ruled Humankind for 500,000 Years." You can read an excerpt on our website, freshair.npr.org. I'm Terry Gross, and this is FRESH AIR.

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