Mosquito Update

In 2001, Craig Coates of Texas A&M University was developing the tools to make a genetically modified mosquito — with an extra gene that would block viruses and parasites carried by mosquitoes from reproducing. With the added gene, the mosquito would be unable to infect humans or animals with diseases like malaria or yellow fever.

In the past years, other researchers have created mosquitoes with this disease-fighting trait. There’s hope that the same trait could be given to the mosquito that transmits West Nile Virus. If these mosquitoes were released into the wild, they might pass on the extra gene to natural mosquito populations. But Coates says release is still years away — partly because it isn’t known how modified mosquitoes might change in behavior or feeding practices.

Craig Coates: The value of the work in terms of having the transgenic mosquitoes is often lost in the fear of releasing the transgenic mosquitoes into the wild. And right now, the immediate value is for the laboratory studies, without any planned releases.

Coates says that this work is helping scientists learn about mosquito biology — and about how they transmit viruses and parasites. He thinks this knowledge will probably lead to improved drugs or vaccines.

More about genetically modified mosquito

The scientists injected pieces of DNA called “jumping genes” into mosquito embryos. These genes allow the mosquito to produce substances that block viruses and parasites from reproducing — so it cannot pass on the disease to humans and animals.

Dr. Coates believes that the transgenic mosquito will be only one weapon in the arsenal of world health organizations: “I don’t think that any one approach is going to be completely effective, against either the viruses or the malaria parasites in particular and so I think it really needs to be looked at as part of a set of tools or technologies that are going to be used in coordination.”

He also emphasizes that possible release is still many years away. “Again, I just need to stress that this has only been done in a laboratory setting and there aren’t any planned releases of these mosquitoes, and it’s probably going to take quite a long time before anything like that would be contemplated, because we don’t know enough about how in modifying a mosquito we’ve changed their behavior or their feeding preferences, and what would happen if you release, like any transgenic organism, what would happen when you release that into the field, so there’s a lot of work still needing to be done on that side.”

Coates believes that the possible risk of the gene jumping to a different species of mosquito, or other insect, is very low. But even “if an anti-yellow fever virus molecule was transferred into a moth or butterfly, it’s hard to imagine that that would have a detrimental effect on that species”.

As scientists continue to progress in this field, questions will likely begin to focus more on the appropriateness and safety of using transgenic insects outside the laboratory.

Now that they’ve figured out how to get the gene inserted into the mosquito DNA, they are beginning to focus on how the gene will act in the wild. Even if the mosquitoes are unable to transmit disease in nature, “the thing that really needs a lot of research, is how you would spread this genetic trait through the natural population, so you could release millions and you could release millions and millions of mosquitoes, but if there are billions in the wild you may not have a very great impact on the disease transmission, unless you can have the anti pathogen gene or anti viral gene spread throughout that population, and that’s certainly a difficult biological question to answer.”

There are over three hundred species of mosquito in the world, but genetic work has focused on the yellow fever mosquito, Aedes aegypti, which primarily transmits yellow fever, dengue, and avian malaria. The mosquitoes largely responsible for the spread of West Nile virus are of the Culex genus. According to Coates, the technology is available to transform the mosquitoes that carry West Nile virus. “The mosquitoes that transmit West Nile virus could be genetically manipulated such that they no longer transmit the virus. And just being able to genetically modify and study the mosquitoes, we’ll learn a lot more about the mosquito, it’s behavior and development and also a lot more about the West Nile virus as well, and hopefully be able to come up with drugs that block its effect or vaccines that would be useful for the greater population”

Today we control mosquito-borne disease by preventing mosquito bites, and by eradicating mosquitoes. But some mosquitoes, and some parasites too, are developing resistance to the respective pesticides and drugs being used to combat them. In addition, many mosquito borne illnesses have no effective vaccines. Working with mosquitoes on a molecular level has immense value for developing drugs and vaccines used to combat these diseases.

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