How We’re Reducing Disease With Genetically Modified Mosquitoes

We all know mosquitoes as those annoying insects we swat away from our faces. They carry diseases, so we don’t want them anywhere near us. There are over 200 types of wild mosquitoes bugging us across America and the U.S. territories.

Approximately 12 types can spread disease, but most are “nuisance” mosquitoes, which don’t spread germs. Obviously, it’s hard to identify a tiny flying creature, so we need to keep them all away from us just in case.

Aedes aegypti¹ is one of the most common mosquitoes in the U.S. that can spread disease. One of the best-known mosquito-borne diseases is malaria, but Aedes aegypti is associated with 54 viruses². West Nile virus, Zika, and dengue are just three diseases these mosquitoes transmit around the U.S.

With 1 in 150 people becoming seriously ill due to West Nile virus, sometimes fatally, what can we do to prevent mosquito bites?

Aedes aegypti have invaded over 128 countries

Originating in West Africa, Aedes aegypti mosquitoes are poor flyers, so they exploit human activities³ to move around the world. They came to the Americas via the African slave trade during the 15th to 19th centuries before spreading to Asia through commercial trade in the 18th and 19th centuries.

World War II allowed Aedes aegypti to spread even further across the globe. 

They are most common in tropical and subtropical regions, but they also live in temperate areas, including the southern United States, Australia, and southern parts of Europe.

They have invaded over 128 countries⁴, increasing the risk of transmitting deadly pathogens. While economically developed nations can often treat these diseases, less economically developed countries struggle. The rates of morbidity and mortality⁴ are disproportionately high among poorer populations.

People who survive these diseases may end up permanently disabled or disfigured, adding to their disadvantages. 

These risks are compounded as Aedes aegypti mosquitoes typically live near where people do. Why? Because female Aedes aegypti⁵ prefer to bite humans. Male mosquitoes do not bite⁶, but female mosquitoes feed on human and animal blood to get the nutrients they need for egg production.

If a female mosquito bites someone who is already infected with yellow fever, Zika, dengue, or chikungunya, she becomes infected. This means that female mosquitoes can easily spread infection through a population due to their selected make-up (biology, structure, and metabolism), which is called “vector competence⁷.” 

For people living in overcrowded areas where these life-threatening diseases are prevalent, these mosquitoes can quickly threaten human health.

How can we control Aedes aegypti populations?

Disease prevention relies on controlling Aedes aegypti populations. While there are ongoing vaccine trials, there are no effective vaccines available for most diseases spread by these mosquitoes. There are two main approaches for population control:

Source reduction

Aedes aegypti spend their immature, aquatic life stages in water-filled containers, including flower pots, buckets, and old tires. Removing or regularly emptying these containers is essential to controlling these mosquitoes, which is also known as source reduction⁸. 

Insecticides

People use insecticides⁹ to target adult mosquitoes, but it is not a perfect method for eliminating them. Finding and larvicide-treat all the containers Aedes aegypti inhabit can be tricky. 

Typical insecticides¹⁰ aren’t environmentally friendly. Not only can they harm wildlife and pollute water, but they can also harm insect populations that we need, such as bees and butterflies. Insects can also develop resistance to insecticides if we overuse and misuse them, rendering our pest-reducing efforts useless while contaminating the environment and risking wildlife. The mosquitoes in Florida are one of many populations resistant to insecticides¹¹.

As these approaches are limited, scientists have been working on discovering new techniques and tools¹² for limiting mosquito populations and reducing their viral spread. These new tools include selective breeding and genetically modified (GM) mosquitoes.

390 million people become infected with the dengue virus every year

Aedes aegypti mosquitoes spread several diseases, one of which is dengue. Typically, dengue fever has a high survival rate. However, if it isn’t detected early, it can have a mortality rate as high as 20%¹³.

The healthcare burden on less economically developed countries is even more troubling with the addition of the Covid-19 pandemic¹⁴, so it’s vital that we control mosquitoes.

The World Mosquito Program has discovered something amazing: When Aedes aegypti carry Wolbachia, a common bacteria in mosquitoes, it competes with viruses like dengue. This makes it much harder for the virus to reproduce inside the mosquito, reducing the risk of spreading diseases to humans. 

By selectively breeding Aedes aegypti with Wolbachia and releasing them into areas with heavy viral burdens, the World Mosquito Program is reducing disease with impressive results¹⁵. 

Florida Keys - Where 4% of mosquitoes cause nearly all vector-borne diseases

The Keys, a chain of tropical islands off the south coast of Florida, are buzzing with mosquitoes. The invasive species Aedes aegypti makes up about 4% of the mosquito population. Yet, Aedes aegypti is responsible for practically all mosquito-borne diseases transmitted to humans in the region, according to the Florida Keys Mosquito Control District (FKMCD)¹⁶.

In 2009, Florida began seeing cases of locally transmitted dengue before locally transmitted Zika appeared a few years later. Florida is still experiencing an increase in mosquito-borne diseases. In search of a solution, FKMCD approached Oxitec in 2010. Oxitec is a biotechnology company that creates genetically modified insects as a “living insecticide.” 

Instead of relying on dangerous and potentially ineffective insecticides, Oxitec created genetically modified Aedes aegypti to control the local Aedes aegypti population. 

Oxitec experiments -  90% decrease in local mosquito populations

Oxitec has been testing its GM mosquitoes in Brazil, the Cayman Islands¹⁷, Malaysia, and Panama for the last ten years. Remarkably, Oxitec demonstrated that their biotechnology could reduce the local Aedes aegypti population by more than 90%. 

In 2021, Florida started releasing 144,000¹⁸ genetically modified, non-biting male Aedes aegypti engineered by Oxitec.  

Later in 2021, the US Environmental Protection Agency¹⁹ (EPA) gave Oxitec’s larger project the go-ahead. It described Oxitec’s creation as an “experimental pesticide product.” The states released up to 2.4 million genetically modified mosquitoes (GMM) in Florida and California to control local mosquito populations. Oxitec declared the Florida mosquito release a "success."

California detected the first Aedes aegypti in 2013¹⁹. Since then, they have spread to 20 counties throughout California. It’s hoped that this GMM project will reduce the transmission of dengue, chikungunya, Zika, yellow fever, and other dangerous diseases.

How do genetically modified mosquitoes work?

There are two mosquito control approaches used with genetically modified mosquitoes: Population suppression and population replacement. These strategies involve releasing GM mosquitoes into nature.

Population suppression

The Oxitec project in Florida uses the population suppression strategy. This approach aims to gradually reduce the number of mosquitoes in an area to lower the risk of virus transmission.

Typically, population suppression mosquitoes are males modified by a self-limiting gene, which they pass on to their female offspring. The offspring either have a greatly reduced hatch rate, or they might die before reaching adulthood, depending on the scientists’ gene modification. This decreases the population size and reduces the risk of mosquito bites and viral spread.

Population replacement

Population replacement aims to replace a wild mosquito population with modified mosquitoes rather than eradicating them. The modified mosquito variant is resistant to infection with pathogens, reducing the spread of deadly viruses.

This approach also requires the release of mosquitoes so the GM mosquitoes can pass their pathogen-resistant gene to their offspring. Over time, the mosquitoes in that region are less likely to be able to spread the disease.

How are genetically modified mosquitoes created?

Scientists create GM mosquitoes with a technique called embryonic microinjection²⁰. They inject engineered DNA into freshly laid mosquito eggs with a tiny, fine needle. This engineered DNA is often called a transgene, and it integrates into the mosquito genome and activates or deactivates a specific gene. Once these eggs hatch in the laboratory, researchers can release them into the wild. 

Genetically modified mosquitoes carry these two genes:

Self-limiting

Male mosquitoes pass on this gene. It prevents female offspring from surviving to adulthood. Oxitec uses the self-limiting gene in its population suppression projects. 

As the name suggests, the self-limiting nature means that GM mosquitoes will gradually die off²¹ in the wild. Oxitec expects this to happen a few months after it stops releasing mosquitoes in the Florida Keys with the FKMCD. 

Fluorescent marker

This gene sends a protein through the mosquito’s body that glows under a red light. The marker gene helps researchers track and identify GM mosquitoes in the wild.

“There’s no such thing as 100% effective in science”

Understandably, critics aren’t as convinced that these mosquitoes are safe and effective. Dana Perls, the food and technology program manager with Friends of the Earth, said, “There’s no such thing as 100 percent effective in science, yet the public is being asked to trust that Oxitec’s experiment will work and no [genetically-engineered] female mosquitoes will survive. But how do we know that?”

The organization cites a confidential Oxitec document²², which was apparently leaked to GeneWatch UK. In the document, researchers expressed concerns that the GM mosquitoes could survive after coming into contact with tetracycline,  a common antibiotic farmers use in livestock farming.

However, the document also explains rigorous procedures to ensure this doesn’t happen. 

In line with the concerns about tetracycline, EPA regulations²³ state that Oxitec cannot release the mosquitoes within “500 meters of wastewater treatment facilities, commercial citrus, apple, pear, nectarine, peach growing areas, or commercial cattle, poultry, and pig livestock producers.”

This will likely reduce the risk of this GM species interacting and interrupting the biodiversity circle. Aedes aegypti mosquitoes rarely travel more than 150 meters²⁴ from where they’re born as they’re poor fliers.

The World Health Organization (WHO) released an official statement²⁵ on GM mosquitoes in October 2020. The WHO supports investigating all potentially beneficial technologies in the fight against vector-borne diseases (VBD), including genetically modified mosquitoes.

Researchers carried out a survey in 2012²⁶, randomly selecting 400 residences in Monroe County after media and outreach activities took place in Key West and Stock Island. People who knew about the release were more supportive and considered genetic mutation a more natural way of mosquito population control than pesticides.

The main response from the supporters was “anything to reduce mosquitoes.”

Many neutral respondents wanted to know more about the project or had concerns. Strongly opposed participants were most concerned about unintended consequences or disturbing natural ecosystems. Even some of those who were strongly supportive were concerned about the ecosystem. 

Of course, this generates the question: How much information should scientists give the general population about these programs? They could educate people about the risks and benefits. 

What is the Integrated Mosquito Management approach, and how can it help?

The use of genetically modified mosquitoes may be more effective if communities use the Integrated Mosquito Management (IMM)²⁷ approach. The IMM control methods include:

  • Tracking and monitoring the number and types of mosquitoes in an area 

  • Removing standing and stagnant water where mosquitoes lay eggs, i.e., emptying buckets of water, old flowerpots, and other containers 

  • Educating communities about controlling mosquitoes in and around their homes

  • Using larvicides and insecticides to control mosquitoes throughout their life cycle

  • Monitoring how effective mosquito programs are at controlling and reducing mosquito numbers

This approach is particularly important in areas where Aedes aegypti mosquitoes coexist with people, and dangerous diseases can spread easily with limited access to healthcare facilities. 

How to reduce your risk of mosquito bites

Here are some methods to reduce your personal risk of mosquito bites: 

Cover up

Make sure to cover your skin with long sleeves and long pants and wear closed-toe shoes. 

Use repellents: DEET and picaridin

The EPA (Environmental Protection Agency) has extensively studied DEET and has declared that it is safe²⁸. It disguises your smell, and mosquitoes dislike the smell of DEET. 50% DEET products are most effective; 10% concentration only provides 90 minutes of protection.

Make sure you follow the directions on the package to ensure no adverse effects like eye irritation. 

Picaridin is a synthetic chemical based on the black pepper plant chemical piperine, and it’s also a very effective repellent.

Use oil of lemon eucalyptus (OLE/PMD)

A 2015 study found this natural repellent to be as effective as DEET-containing products, especially against Aedes aegypti. 

Be sure not to confuse the oil of lemon eucalyptus with the similar sounding “pure oil of lemon eucalyptus,” an ineffective essential oil. You can also look for the chemical name para-menthane-3,8-diol (PMD) to double-check you have the correct oil.

Pour away standing water

As mosquitoes start their life cycle in standing water, make sure you empty rainwater out of any buckets, plant pots, or other containers regularly.

Keep your yard tidy

Mosquitoes love hiding in the grass and fallen leaves, so keeping your yard neat can keep them away.

What’s the buzz?

Mosquitoes are an important part of nature. They help regulate ecosystems and provide food for birds, reptiles, amphibians, and mammals. But when they become too abundant, they can cause problems for humans.

Invasive Aedes aegypti mosquitoes pose a real threat to human health as they carry disabling and deadly diseases like chikungunya and dengue. With the help of science, we’re discovering innovative ways to tackle the issue.

Still, it’s not just up to science: We also need to play our part. That means continuing to educate at-risk communities and removing standing water sources, so mosquitoes have fewer places to lay their eggs and develop into fully fledged, dangerous adults.

Hopefully, with the combination of public knowledge and scientific advancements, we can reduce the impact of these terrible diseases on communities worldwide.

Sources:
  1. Aedes aegypti | Wikipedia

  2. Aedes aegypti (linnaeus, 1762) | Walter Reed Biosystematics Unit (WRBU)

  3. Phylogeography of Aedes (Stegomyia) Aegypti (L.) and Aedes (Stegomyia) Albopictus (Skuse) (Diptera: Culicidae) based on mitochondrial DNA variations (2005)

  4. Evaluation of genetically modified mosquitoes for the control of vector-borne diseases | World Health Organization

  5. Why do female Aedes aegypti (Diptera: Culicidae) feed preferentially and frequently on human blood? (2001)

  6. Wolbachia-Aedes mosquito suppression strategy | National Environment Agency

  7. How do virus-mosquito interactions lead to viral emergence? (2019)

  8. Larval control and other vector control interventions | Centers for Disease Control and Prevention

  9. Adulticides | Centers for Disease Control and Prevention

  10. Insecticides: Killing the good and the bad | Encyclopædia Britannica

  11. Mosquitoes becoming resistant to insecticide by sensing toxins through their legs | SciTechDaily

  12. Suppressing mosquito populations with precision guided sterile males (2021)

  13. Dengue | Medscape

  14. Dengue and severe dengue | World Health Organization

  15. Impact | World Mosquito Program

  16. Florida Keys Mosquito Control District (FKMCD)

  17. Successful suppression of a field mosquito population by sustained release of engineered male mosquitoes | ResearchGate

  18. First genetically modified mosquitoes released in the United States | Nature

  19. U.S. EPA approves oxitec mosquito pilot projects in California and Florida | Keys Mosquito Project

  20. Microinjection (2019)

  21. Genetically modified mosquitoes | IFAS Extension University of Florida

  22. Eliminating tetracycline contamination (2017)

  23. Following review of available data and public comments, EPA expands and extends testing of genetically engineered mosquitoes to reduce mosquito populations | United States Environmental Protection Agency

  24. Frequently asked questions | World Mosquito Program

  25. Evaluation of genetically modified mosquitoes for the control of vector-borne diseases | World Health Organization

  26. Awareness and support of release of genetically modified “Sterile” mosquitoes, key west, Florida, USA (2015)

  27. What mosquito control programs do | Centers for Disease Control and Prevention

  28. Deet | United States Environmental Protection Agency

Victoria is a writer from the UK with a keen interest in health and science. She loves writing about mental health, scientific advancements, and dispelling pseudoscience. When she’s not writing sass-laden articles, she walks her rescue dogs, giggles at anxiety memes, eats chocolate, and absorbs useless knowledge for quiz shows.

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