Release the Beast? Genetically modified mosquitos for diease control

By Gabriel Ferrante

Insects are both a pain and an essential part of our lives and livelihoods – even if it isn’t obvious at first. For example, many species of Mosquitos carry lethal diseases, but are outnumbered by others performing essential services maintaining ecosystems.

The two sides to this arthropod coin mean that common strategies for dealing with many insect pests – like spraying pesticides – cause collateral damage to harmless species that perform vital functions, such as pollinators. We are currently undergoing an ecological disaster and the widespread use of pesticides is one of the causes in the decline of pollinators which are responsible for the reproduction of approximately 75% of the world’s food crops.

Other strategies are needed to help manage these pests to minimise any further damage.

The company Oxitec is an example how genetic technologies can be used in managing unwanted species in a sustainable way.

Oxitec jumped to the headlines in March with permits being issued by the United States Environmental Protection Agency (EPA) to allow the release of around 2.4 billion male mosquitos over two years in Florida and California.

This is part of an expansion of their existing trial of releasing a genetically modified mosquito species in a bid to suppress the species Aedes aegypti in the USA. Aedes aegypti also known as the yellow fever mosquito has a main role in spreading debilitating diseases such as Dengue, Chikungunya, Yellow Fever and Zika virus in many countries. Aedes aegypti also is an invasive species in many subtropical regions, spanning from the south-eastern US to the Pacific Islands and South-East Asia.

Oxitec’s signature technology involves the use of a ‘self-limiting’ gene which only activates in female mosquitos after reproduction. This gene produces a protein that hijacks the protein-producing machinery of female mosquitos’ cells as they grow, stopping the cells’ ability to make other proteins and killing them before they become adults. Introducing this gene into wild mosquito groups through reproduction ensures only Aedes aegypti is targeted with pinpoint precision, resulting in a generation of male mosquitos and a collapse in their population’s size.

A previous Brazilian trial resulted in the suppression of 95% a local Aedes aegypti population in 13 weeks

The decision to release more males in the US comes after the success of trials held in 2021 in the Florida Keys. These trials verified that the self-limiting gene is still effective in the field, that the Oxitec male mosquitos were able to find and mate with wild Aedes aegypti, and that no genetically modified mosquitos remained in the wild after more than 3 months.

Evidence is building up that this technology does work, with a previous Brazilian trial resulting in the suppression of 95% a local Aedes aegypti population in 13 weeks. However, the question remains if the technology reduces the population of mosquitos enough to stop them spreading disease in the field.

To this point Oxitec has received a 6.8-million-dollar grant from the Wellcome Trust to expand and upscale their ‘FriendlyTM’ mosquito line and plans to make it cheaper and more accessible.

Part of this fund would be directed towards testing if their technology reduces transmission of Dengue fever in urban environments in the district of São Paulo region in Brazil. In this direction, partnerships with the City of Indaiatuba and the Tietê Bus Terminal in São Paulo aim to reduce the amount of Aedes aegypti which caused over 139,400 dengue cases in 2021.

But Aedes aegypti isn’t the only troublesome bug on Oxitec’s radar, a visit to the company’s website would show a wealth of different species of pests that are being targeted with their technology. These range from self-limiting armyworms, (Spodoptera frugiperda – a type of caterpillar that shrugs off pesticides and GM plant toxins to then munch upon everything from sorghum to rice) to the two malaria carrying mosquitos Anopheles albimanus and stephensi.

The beauty of self-limiting technology such as this is that unless the organisms modified are exposed to the antibiotic tetracycline, (which is used by Oxitec to inactivate the self-limiting gene), the gene itself will disappear after a couple generations, leaving no lasting legacy in insect populations.

Genetic technologies may still bear further fruit in other applications in the future, but that remains to be seen. It is only ensured if they are well researched, regulated, ethically used, and heavily monitored.

Image: CDC/ Dr. Harry D. Pratt

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