The Cure For Malaria Could Be In A Mosquito's Gut

IRA FLATOW, host:

This is SCIENCE FRIDAY, from NPR. I'm Ira Flatow.

Why do some blood-sucking insects like mosquitoes transmit diseases like malaria, but others, like, bedbugs, do not? Could it have something to do with the insect's immune system? And if it is, could we tweak a bug's immune system a little bit to make it a little better at fending off parasites and keep them from infecting people?

The possibility is out there because this week, researchers say they have found something in the mosquito immune system that helps the mosquito kill malaria parasites on its own, before the bug has a chance to bite another person and transmit the disease.

That research appears in the journal Science. And just how far are we from making wild mosquitoes malaria-proof? Joining me now to talk about it is Carolina Barillas-Mury, a senior investigator at the Laboratory of Malaria and Vector Research at the National Institutes of Health in Rockville, Maryland. She joins us by phone.

Welcome to SCIENCE FRIDAY, Dr. Barillas-Mury.

Dr. CAROLINA BARILLAS-MURY (Senior Investigator, Laboratory of Malaria and Vector Research, National Institutes of Health): Thank you. Good afternoon.

FLATOW: Let's talk about this research. Tell us about your study. It's two groups of mosquitoes, you feed them on a mouse infected - blood with malaria. And then what happened?

Dr. BARILLAS-MURY: Yes, one of the rooms was placed at a temperature where the parasites cannot infect the mosquitoes. So these mosquitoes were fed this blood, but they were not infected, while the other group was infected.

And what we did is then we waited one week or two weeks, and two weeks later, we took these same two groups of mosquitoes, and this time we infected both in a mouth and kept them at a temperature where both will be infected. And we asked: Has the previous exposure to the infection improved the way these mosquitoes respond? Are they better able to kill plasmodium the second time around?

And we got very clear results and very striking, because they did much better the second time around, and this is against what people thought about insects. Most people think that the immune system of insects is not able to learn, and our study says that the system is more flexible, and it indeed can learn to respond better.

FLATOW: So they developed some immunity to the malaria parasites. The second time, they were not so, I guess, attacked by them.

Dr. BARILLAS-MURY: Yes. So what we think happens is that in a yira(ph) mosquito - that is, a mosquito that has never had an infection with malaria - by analogy, we would say that operate in a green level of alertness. But if an infection has happened, the mosquito has the ability to increase the surveillance level to a code red and be much better prepared.

And it does this by increasing the number of sentinel cells. Mosquitoes have cells swimming in their blood that are detecting to see if everything is okay. We can think of them like the security guards or sentinels. And once they see that something is wrong, they begin to attack the microbe, the enemy, and send also signals to the rest of the body to call for help.

And mosquitoes that have had an infection have more sentinels. So they're better at detecting the parasite and much better at fighting it.

FLATOW: So I guess the ultimate goal here would be to find some way in the wild of getting these sentinels to attack the malaria itself inside the mosquito.

Dr. BARILLAS-MURY: Exactly. This is exactly the point. Now that we know that this can happen, so the system can learn, we want to understand we know that something is producing the blood of these mosquitoes because if we can take the serum of these mosquitoes that have the learning and put it in a new mosquito that just came out as an adult, that has no experience, we can transfer.

When we do this, we inject this serum, then this new mosquito acquires two things. It has - makes more sentinel cells and becomes very good at fighting malaria. So we can transmit this learning, let's say.

Now, what is the substance? And is there a way in which we can induce the production of this substance in the field, applied situation. I think this is where our future studies will head.

FLATOW: Okay, do you have any idea what that substance might be at this point?

Dr. BARILLAS-MURY: We do not know. We have some preliminary experiments, but it's too early to tell. We're using classical biochemistry, trying to see: What are the characteristics of this factor? And there's some tricks we can use. Is it sensitive to temperature? Is it a protein? Is it a peptide? And is it a lipid? And we're doing classical studies right now, but it's too early to tell. We're very excited, but it's early, too.

FLATOW: Yeah. I can see why that could be. Let me just diverge a little bit here and ask you about - you're an insect specialist. We've been talking about bedbugs a lot in this country.

Dr. BARILLAS-MURY: Yes.

FLATOW: What is it about bedbugs that they are immune from the diseases that they - they don't carry diseases.

Dr. BARILLAS-MURY: Yes. So I think that most insects do not carry diseases. Basically, it's hard for, for instance, a parasite to survive in an insect. If you think of a parasite in a mosquito, it has to go through an obstacle race.

First, they take up - they're taken up with the blood, and they're there, and they can find them also in bedbugs. So the agents get ingested. So they're inside the mosquito. But then they have to do many things.

They have to survive digestion, because the bug is going to try to digest the blood and produce a lot of enzymes that could kill the parasite. The insects also surround the blood with a layer to protect themselves from the immune cells of the vertebrates that are in the meal.

So they wrap it up, and some parasites cannot get out of this layer that we call peritrophic matrix, or peritrophic sac. And if they are able to pass this layer, then they have to invade the cells of the intestine. And these cells, we know, defend themselves very strongly.

And if they survive this, then they face the immune system of the mosquito when they reach the blood. So getting through all these different barriers is very complex, and in most cases, most parasites fail.

But once in a while, there's a rare event in which one is successful, and this parasite is the big winner because now, instead of being local, it can fly, and it can jump from person to person. And it's much more efficient being transmitted.

And because they cause so many problems, these parasite-mosquito pairs become very famous because they cause a lot of problems. But most insects are nice. Even most - an awful lot of mosquitoes are nice. Most of them, well, they bite us, but they don't make us sick.

FLATOW: That's a good thing.

Dr. BARILLAS-MURY: Yes, it's a good thing. So I think that the possibility of this happening is rare in nature. So it takes hundreds of years of exposure and many attempts until the right parasite finds a bug that is just right for him.

FLATOW: All right. I want to thank you for taking time and I want to wish you good luck in finding that missing factor that we don't know about.

Dr. BARILLAS-MURY: Oh, thank you very much.

FLATOW: Yeah. Thanks for taking time to be with us today. Carolina Barillas-Mury is a senior investigator at the Laboratory of Malaria and Vector Research at the National Institutes of Health in Rockville, and she was joining us by phone.

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