Genetic engineering gives mosquito control an upgrade

General Studies Paper 3

Context

• Throughout human history, mosquitoes have constantly buzzed in the background of human existence, irritating us with their incessant bites and occasionally wreaking havoc by transmitting deadly diseases.

About

• The earliest known mosquitoes from the fossil record date back at least 70 million years, and evidence of mosquito-borne diseases like malaria dates back to Egyptian mummies from 2000 BC.
• Apart from malaria, which claims the lives of over half a million people every year and infects close to 250 million, mosquitoes serve as vectors for various other diseases.
• These include dengue, Zika, lymphatic filariasis, and yellow fever. Understandably, our relationship with these tiny, blood-sucking insects has been far from cordial.

Help from sequencing tech

• The rapid urbanisation of the world’s populations, especially in many large and economically developing countries like India, has led to annual surges in mosquito-borne illnesses like dengue.
• Together with climate change and its cascading consequences, mosquito-borne diseases have expanded into new territories. A notable example is the indigenous cases of dengue in France in recent years.
• It is not surprising then that mosquito control has taken centerstage today and the battle continues unrelenting with an array of tools – from mosquito nets to insecticides and the use of symbionts like Wolbachia.
• But with insecticide resistance in mosquitoes rising to alarming proportions, it has become imperative that newer approaches to mosquito control gain prominence, even despite the availability of a first-generation malaria vaccine that officials in different countries are currently implementing in a pilot in endemic regions.
• Notably, researchers from the University of California, the Tata Institute of Genetics and Society, and the Institute of Bioinformatics and Applied Biotechnology have helped prepare high-quality reference genomes for Anopheles stephensi, a major malaria-vector mosquito.
• The availability of these high-quality sequences, coupled with our capacity to genetically manipulate them, offers unprecedented opportunities.

The gene drive

• The fundamental idea behind genetic manipulation of mosquitoes is to systematically control their populations by interfering with their reproduction.
• A major one in this endeavour is gene-drive technology, whose end result is for mosquitoes to selectively inherit some genes, rather than the inheritance to follow the rules of Mendelian genetics.
• Here, a protein cuts the mosquito’s DNA at a part that doesn’t encode a particular sequence in the genome.
• This triggers a natural mechanism in the cell containing the DNA to repair it and forces the cell to incorporate a sequence, called the drive sequence, into the damaged portion.
• As a result, the malaria parasite won’t be able to replicate inside the mosquito’s gut.
• In a recent paper, researchers at Imperial College London genetically enhanced a gene expressed in the midgut of mosquitoes to secrete two antimicrobial substances called magainin 2 and melittin.
• They are detrimental to the Plasmodium parasite’s development in the midgut and also reduce the lifespan of female mosquitoes.
• Computational modelling studies have suggested that this approach could significantly disrupt malaria transmission.

Benefits as well as risks

• In 2020, the U.S. Environmental Protection Agency authorised the release of a genetically modified mosquito called OX5034 in counties in Florida and Texas.
• Oxitec developed this mosquito with a gene sensitive to an antibiotic, tetracycline.
• Genetically modified male OX5034 mosquitoes mated with female mosquitoes but the self-limiting gene prevented female offspring from surviving.
• As a result, the male mosquitoes would disappear from the environment after around a dozen generations.
• These technologies can bring benefits as well as risks, in different ways. An immediate implication is that the drastic reduction in the mosquito population could alter food chains and ecosystems that involve mosquitoes.
• So it’s likely that the gap in the food chain could be ‘invaded’ by other mosquitoes or in fact other insects.

Way forward

• Critics have expressed concerns about unintended consequences, such as unforeseen ecological disruptions or the potential for engineered genes to spread beyond target mosquito populations.
• The battle between mosquitoes and humankind seems to be a timeless struggle, a testament to human ingenuity against frustrating troublemakers aided by evolution.