The Genetically Modified Mosquito

Posted on Categories Consumers, General

I was recently asked a series of questions on the release of the genetically modified mosquito produced by Oxitec. Snippets of my responses were published in a Forbes Opinion Article entitled “You can help stop these deadly mosquitoes“, written by Kavin Senapathy, who also asks a number of other scientists questions related to the potential release of the Oxitec Mosquito in the Florida Keys .

Here is my email below:

Do the benefits of the pilot release of Oxitec mosquitoes in the Florida Keys outweigh the risks? What are the real risks, and how do they compare with public perception of the risks?

Before delving into the risks, let’s first discuss the technology and method of management. The Oxitec mosquitoes are essentially a type of sterile insect technique (SIT, for short) – a method used as early as the 1950’s to eradicate screwworm from southern USA. The screwworm is a parasite of warm-blooded mammals (i.e. cattle), wildlife, pets, and zoo animals, that would lay eggs on the edge of open wounds. The eggs would hatch and the larvae would dig into the wound, which would result in more bleeding, and more screwworms laying eggs. Infestation by screwworms could kill an animal within 5 – 10 days, which was devastating to the livestock industry. The solution that ended up eradicating the screwworm entirely out of North America was due to the sterile insect technique. In short, male screwworms were mass produced in labs and irradiated with radioactive material, which would render them infertile. They would release these screwworm adult males in the field in very large numbers to outcompete and outnumber the fertile males in the wild. As a result, the infertile males that were released would mate with the females, and the females would lay unviable eggs. The only problem to this technique was in how they produced the sterile males: irradiation, which often resulted in malformed or weak males that were essentially a “waste” upon release.

Fast-forward to today. We have now developed incredibly effective genetic manipulation techniques that allow us to cut and paste very specific sequences of code pretty much anywhere within a genome. Mosquito larvae live in the water and feed on small microorganisms before becoming adults. The Oxitec mosquito has a genetically modified gene within it that doesn’t allow the offspring to develop past the larval stage – it simply dies. So tons of male oxitec mosquitoes are released into the environment, and they outcompete the wild males to fertilize females, and their offspring simply don’t survive, thereby drastically decreasing in mosquito population. Oxitec has also found an effective way at being able to rear these mosquitoes in mass quantities: the oxitec lethal gene can be “turned off” in the presence of a certain concentration of tetracycline far greater than that found in the environment. Oxitec can mass produced these mosquitoes in their rearing facilities in the presence of tetracycline to keep breeding their populations, and then release them out in the environment to get the lethal effect on the next generation offspring.

Photo of Aedes aegypti
Feeding Aedes aegypti, the vector of Chikungunya, zika, and dengue. Photo taken by Dr. Gabriel Hamer, Texas A&M.

The risks: There are two risks to really consider – the risk of using the oxitec mosquitoes and the risks of not using the oxitec mosquitoes.

Risk of using oxitec mosquitoes: We have seen some of the potential risks associated with using genetically modified foods, such as the rise of super-weeds in response to over-use of glyphosate on roundup ready genetically modified crops. However the case with the oxitec mosquito is much different. The release of oxitec mosquitoes does not rely on the constant use of a single insecticide and if for by some overlooked method the gene ‘jumped’ to another closely related mosquito, it would simply result in the death of that individual mosquito’s offspring in the larval stage. There is very little evidence to support worrisome risks associated with worst-case-scenario of the genetic modification technique in the oxitec mosquito.

The other risks include the impact of the drastic decrease in one mosquito population on other mosquito populations or higher order organisms that may feed on Ae. aegypti. Although Ae. aegypti is an invasive, it has been in North America for at least a few hundred years now, so it can be considered an ‘established’ species with organisms that perhaps have Ae. aegypti as a healthy part of their diet. However, this isn’ the first time we have tried to eradicate Ae. aegypti. There was an eradication program back in 1965 for North and South America that combined the use of removing Ae. aegypti habitat (i.e. standing water in urban areas) and insecticide sprays to eradicate this mosquito. Although the program helped drastically reduce, and even in some areas eradicate Ae. aegypti, they eventually ran out of funding and ceased the effort. From what we know, we didn’t see any major ecological ramifications of the 1965 eradication program, which even included insecticide sprays, so it can be argued that the ecological risks of a more targeted eradication program (i.e. sterile males that will only affect offspring of Ae. aegypti females) are relatively negligible. Additionally, there is a report produced by the USDA on “No Significant Impact” of the release of the Oxitec Mosquito in the Florida Keys.

On the other hand is the risk of what happens if we do not allow the release of the oxitec mosquito. Ae. aegypti is a vector of several viruses, including yellow fever, dengue, chikungunya, and zika virus. According to the CDC, approximately 2.5 billion people live in areas with risk of dengue transmission, with 500,000 cases of dengue hemorrhagic fever and 22,000 deaths annually, mostly amongst children. With the current increasing risks of chikungunya and zika virus in North America, the risks are becoming even more real for everyday Americans. Stopping the Oxitec mosquito could result in a great delay in our ability to reduce the two species of mosquitoes responsible for the transmission of most of these viruses and result in several hundreds of thousands, or millions, of people continuing to suffer and die.

Since ae. aegypti is an invasive species in much of the world, should we not worry about drastically reducing or eliminating its population?

I answered this bit above, but there is another ethical question that entomologists have been asking recently. We are achieving the technology that would allow us to completely eradicate species of our choosing from existence: is it our right or our place as humans to do so? Who gets to decide whether a species is eliminated from the earth? As such, some entomologists have become more interested in seeking alternatives to species eradication. In the case of Ae. aegypti, it may involve introducing a symbiotic bacteria that can infect the mosquito and reduce virus transmission, in order to eradicate the virus, rather than eradicating the mosquito.

Aedese albopictus, also a vector of chikungunya, dengue, and zika virus, but currently not being proposed for control using the sterile insect release via genetic modification technique. Photo courtesy of Dr. Forrest Mitchell, Texas A&M
Aedese albopictus, also a vector of chikungunya, dengue, and zika virus, but currently not being proposed for control using the sterile insect release via genetic modification technique. Photo courtesy of Dr. Forrest Mitchell, Texas A&M

The website calls for the public to voice support to the FDA for the Oxitec mosquito trial. Should the public trust the information on the site, since it’s from Oxitec? Should companies play a role in explaining these issues to the public?

Personally, I rarely suggest using only one source of information to make a decision. There are several research articles with the actual techniques used to genetically modify the mosquitoes and many other reviews of concerns or positive articles on the oxitec mosquito. Just always make sure that the sources you are using are reliable – are they from people in the field of entomology, genetics, or ecology? Are they people that have a dedicated career with a good track record? Are they recognized and validated by their peers in their field? I guess what I’m trying to say is that an angry person with a blog is not a reliable source.

I think companies should absolutely play a role in educating the public, but I think university and non-governmental institutions alike also play a role in ensuring that there is a source of unbiased and accurate information available as well. Afterall, a company is trying to sell an idea or a product, so they may downplay or overlook some of the potential negative consequences.

Should Americans and those in the developed world be concerned about Ae. aegypti? After all, it’s not in your backyard if you’re not in certain areas of the southern USA, right?

Although it’s true that Ae. aegypti is found mainly in southern US, predictions of the future of global climate change increase the range of Ae. aegypti substantially. Where approximately 3.5 billion people would be at risk of dengue transmission in 2085 without the effects of global climate change, about 5 – 6 billion people (50 – 60% of global project population) are predicted to be at risk due to increasing temperatures by 2085. So even if it’s not a problem in your backyard now, it very well can be!

Do you think that public opinion will influence the FDA’s decision with regard to the pilot release of Oxitec’s mosquito in Florida?

I honestly don’t think I’m the most qualified to answer this, as I have only been in the USA for the last two years, so I am not familiar with the history of decisions made by the FDA based on public comments. However, according to the FDA themselves, they claim that the public commenting certainly does have influence on policy that they create, and even give an example of how Americans influenced what ingredients they want or don’t want allowed in their white bread. They also do state that the decision is not merely made on the “number” of comments, but rather the content of the comments. As such, public comments will most likely be most effective if they are concise, well-informed, and raise issues/concerns that have some data or research to support them. Comments that suggest that genetically modifying mosquitoes may result in a superior race of insects that will outperform humans and eventually become our overlords will likely not be taken seriously.

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