Sex-changing mosquitoes fight Zika

Sex-changed mosquitoes might be the secret to defeating Zika, two Virginia Tech scientists propose.

Using gene editing to turn disease-transmitting females into harmless males could be a cheaper and more effective way to wipe out mosquito-borne diseases than other methods, the scientists write in Trends in Parasitology.

But it’s a long road ahead.

By proxy, mosquitoes are one of the biggest global killers.

With the Zika outbreak declared a global public health emergency, the dengue virus estimated to annually infect 390 million and malaria reported to have killed 438,000 last year alone, scientists are putting their heads together to devise a way to wipe out disease-carrying mosquitoes.

It’s the females that cause the trouble. Unlike the harmless nectar-feeding males, the blood-sucking females transmit diseases to humans.

Releasing sterile, transgenic males to compete with the wild, fertile ones, thereby curbing reproduction, is one approach, and has been successful for controlling dengue in field studies. But that strategy is only effective if sterile mosquitoes are continually released – a costly, long-term exercise.

A better solution could be using the new, efficient CRISPR-Cas9 gene editing technique to stop any newborn mosquito from becoming female in the first place, the authors say.

A study published in Science last May uncovered the first known mosquito sex-determination gene.

The gene produces the so-called “M factor” which, when slotted into a female’s genome, prompts them to grow male genitalia. In disease outbreak regions, mosquitoes engineered to produce this factor could be released and pass the sex change machinery on.

“We are at a turning point both in our understanding of how mosquitoes determine whether to become a male or a female, as well as our ability to permanently modify wild populations using gene drive techniques,” said entomologist and review author Zach Adelman.

But the technology has yet to be tested and has many more hurdles to jump. For one, it’s not clear whether the M factor is found in all mosquito species or for how long the system would be effective.

And even though UK researchers have recently been given the go-ahead for CRISPR-Cas9 gene editing in human embryos, there are big ethical concerns for insects. If just a few mosquitoes were to escape a study site during testing and establish themselves in the wild, it’s not clear how they could be removed.

The National Academies of Sciences, Engineering and Medicine are now developing guidelines for genetic modifications of non-human organisms.

“Moving forward, partnerships with supportive governments, local collaborators and a willing public will be crucial to establishing field-based testing in areas that are most impacted by mosquito-borne diseases,” Adelman said.

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