GM Mosquitoes – the key to dengue prevention?

Dengue fever or dengue hemorrhagic fever is caused by the dengue virus. The dengue virus is only transmitted by adult mosquitoes - mostly the Aedes aegypti mosquito. There are 4 types of dengue viruses, called DENV1, DENV2, DENV3 and DENV4. If you become infected with one type of dengue virus you will likely have a mild infection and develop lifelong immunity to that virus serotype. Immunity to the other serotypes of the virus only lasts for a short time. If you get re-infected with a different serotype of the virus, that is usually when severe complications, like the hemorrhagic fever, occur. This is a huge problem with dengue because more than one serotype is usually present in a geographic location. It has been observed that if you are infected with DENV1 then get DENV2 or DENV3, or if you have DENV3 then get DENV2 you are more likely to develop dengue hemorrhagic fever.

Dengue virus is a vector borne virus, which means that there is little person-to-person spread in the absence of mosquitoes. A mosquito acquires the virus by biting an infected person. The virus can live in the mosquito but has no detrimental effects. The mosquito is infected for life and is able to transfer the virus to a person with just a single bite. There currently aren’t really any means to prevent dengue virus infection besides using pesticides, bug spray, eliminating standing water, using mosquito nets and keeping skin covered. There also really isn’t any direct treatment for the virus – usually just the symptoms, like dehydration, are treated.

In Brazil over 10 million genetically modified mosquitoes have been released over the past year to try to combat dengue virus infections. The GM mosquitoes are male and carry a gene that causes their offspring to die before reaching adulthood. Since only adult mosquitoes spread dengue virus, this should have a significant impact on spread of the virus. It has been found that currently 85% of the mosquito eggs carry the transgene, which indicates the GM males are overriding the wild population and successfully producing offspring. This should decrease the Aedes aegypti population and dengue transmission. Since relatively little time has passed since the GM mosquitoes have been released, no information is available yet on whether this is having any effects on dengue virus rates.

What is pretty cool about this is that the scientists surveyed the residents of the area where they were going to release the mosquitoes before they did anything, to find out if they were ok with the plan. They found that 90% of the residents were in favour!

If successful, this strategy could potentially eradicate dengue virus infections worldwide! The articles online (http://www.scidev.net/en/health/genomics/news/brazil-tests-gm-mosquitoes-to-fight-dengue.html) didn’t contain a lot of information and I had some questions about the uses of this GM technology. I couldn’t find any information about if these GM male mosquitoes will eventually lead to eradication of Aedes aegypti mosquitoes, or if there are concerns that other types of Aedes mosquitoes that can spread dengue would just take over transmission. I was also curious if a similar strategy might be under consideration for other mosquito-borne viruses, like West Nile virus. Finally, as with all GM organisms, there are concerns that the offspring could breed in the wild and lead to unpredictable results. It was stated that the scientists were confident no viable offspring could be produced by transgenic mosquitoes, but no explanation about this was given. All in all, very interesting, but I want more info!

C.