Engineering a Better Mosquito

Several years ago, in one of my introductory biology classes, I mentioned that one of the most promising ways to fight diseases, such as malaria, might be to genetically engineer a better mosquito. As you may expect, the looks from the around the classroom were fairly consistent – their usually slightly-off center instructor had finally stepped over the edge. After all, shouldn’t we be getting rid of mosquitoes, not making them better?

While humans may be fairly adept at driving species into extinction, we seem to have a problem when it comes to mosquitoes. For diseases such as dengue  and yellow fever, the mosquito we are dealing with, Aedes aegypti (shown below), has proven to be a formidable foe. The species has a very short generation time (10-14 days), and can reproduce in environments with very small amounts of water (planters and old tires are frequently used). In addition, they have exhibited the ability to very quickly evolve resistance to many forms of insecticides. Despite modern efforts to control this species, it is not only surviving, but doing well.


By James Gathany (PHIL, CDC) [Public domain], via Wikimedia Commons

One of the diseases that this mosquito is involved with is dengue fever. This is a multistage infection. The disease starts off with a high fever, pain behind the eyes, and muscle pain. But the real damage starts to occur about 24-48 hours after the fever breaks, when the capillaries of the body can become leaky, resulting in dengue hemorrhagic fever (DHF) , which may result in circulatory system failure and death. Like many hemorrhagic fevers, there are no medications or treatments.


By Mikael Häggström [Public domain], via Wikimedia Commons

 

Despite the fact that dengue fever is caused by a virus, there are no vaccinations, and preventive mechanisms focus on avoiding mosquito bites. But since dengue occurs in the tropical regions of the globe, over 40% of the world’s population is exposed to the mosquito, and there are believed to be over 100 million new cases per year. Avoidance of mosquito bites for densely populated areas within the range of Aedes mosquitoes is becoming increasingly difficult.0

So how does one control the spread of a disease that utilizes a host species that is resilient to most of our efforts? The answer might be not to kill the mosquito, but rather to make it an inhospitable host for the virus that causes dengue. And the secret to this is Wolbachia, a species of bacteria that is a common parasite of many insect species. Wolbachia has been studied extensively in species of insects such as Drosophila (the fruit fly) and it is well-recognized as having the ability to moves rapidly through populations of insects.

Researchers have shown that the dengue virus does not reproduce well within a Wolbachia-infected mosquito. Since dengue fever can only be passed on using the mosquito as an intermediate (there is no person-to-person transmission), if the number of dengue-carrying mosquitoes can be reduced over an extended period of time, it may be possible to break the cycle of infection. This opens up the possibility of actually releasing millions of Wolbachia-infected Aedes mosquitoes into a given area, with the hopes of breaking the dengue-virus life cycle. Trials are currently underway, and if successful, may open up a new chapter in how humans regulate the spread of some of the most deadly diseases on the planet.

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