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Why can mosquitoes carry deadly viruses without succumbing to them and live on to give humans West Nile, dengue fever, and a host of other fatal illnesses. According to new research, the insects' primitive immune systems recognize that the viruses are dangerous and slice the microbes' genetic material into harmless pieces.

But while fighting the viruses, mosquitoes pass them to people (and in some cases other animals), who do not seem to have the capacity to chop them up. The finding, which was published in today's Proceedings of the National Academy of Sciences, could lead to therapies to beef up human immunity against such microbes or ways to remove mosquitoes' defenses so that they kick the bucket when invaded by viruses instead of surviving to spread them far and wide.

The prevailing theory had been that these viruses and mosquitoes lived in harmony. But entomologists found quite the opposite to be true. "We were shocked," lead author Kevin Myles told ScientificAmerican.com, "This had long been viewed as a very benign relationship."

Myles and his colleagues at Virginia Polytechnic Institute and State University in Blacksburg, Va., discovered the mosquito's secret when they infected the insects with a virus that is a close relative of disease-causing microbes. They found that the mosquito's immune system cut up the virus' genetic material so that the insect didn't get ill. The team then infected the mosquitoes with a genetically modified virus that blocked their chopping mechanism. Those mosquitoes were unable to mount an attack against the invader and died off two to five times more quickly than did mosquitoes infected with the normal virus.

Understanding how mosquitoes fend off viral attacks might improve human health in the future, says study co-author Zach Adelman.

"If you could genetically modify a mosquito, then the mosquito would die upon becoming infected," he says. "This work hints that that's a possible application." He adds that future antiviral therapies for people may be fashioned to mimic the mosquito's virus-killing tricks. "If we could understand how the mosquito is doing such a good job," he says "maybe we could learn something about how to treat this disease in humans."

(Malaria is a parasite, not a virus, and so it's unclear whether these techniques would work for this particular mosquito-borne disease.)

(Image courtesy of the U.S. Centers for Disease Control.)

4 Comments

1. 1. DavidMcC 05:44 AM 12/2/08

   I thought it had been known for several years that there is a parasite that makes mosquitos dangerous, and that it does so by making life very difficult for the poor old mosquito - it has to work very hard to get any benefit from the blood it sucks, so that it has to infect a lot of victims in its struggle to survive. Good for the parasite, bad for both the mosquitos and us! Unfortunately, I don't have a reference.
   "...or ways to remove mosquitoes' defenses so that they kick the bucket when invaded by viruses instead of surviving to spread them far and wide."
   Sounds like it would be an uphill struggle, because unmodified mosquitoes would be more successful than the modified ones. Better to engineer a harmless but successful form than a still-dangerous, but unsuccessful one, surely.
   

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2. 2. krabcat in reply to DavidMcC 06:18 AM 12/2/08

   only female mosquitoes bite. they do this to get the proteins necessary to produce fertile eggs
   www.wisegeek.com/why-do-mosquitoes-bite.htm
   
   no parasite

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3. 3. JamesDavis 07:57 AM 12/2/08

   Wouldn't the mosquitoes have the ability to transfer any genetically modify material to us before they die? With that in mind, I do not think it would be a good idea to infect the mosquito with something that will kill it. Why not work on infecting humans with the mosquitoes ability to cut up the viruses. Logic tells me that would be safer for humans. Black walnut extract kills parasites and other worms and it is safe for human consumption.

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4. 4. DavidMcC in reply to krabcat 08:07 AM 12/2/08

   Krabcat, I'm sure you're right about most of the infections passed on by female mosquitos, but I was thinking of female anopheles mosquitos infected by plasmodium.

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