Transgenic fungus reduces malaria mosquito populations

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New research has described the first semi-field trial for a transgenic approach to combatting malaria, demonstrating that a naturally occurring fungus engineered to deliver a toxin safely reduced mosquito populations by more than 99%.

The study, recently published in Science, assessed the fungus in a screen-enclosed simulated village in Burkina Faso.

The researchers used a strain of the fungus, Metarhizium, that was specific to mosquitoes and engineered it to produce a toxin, an insecticide termed Hybrid, that kills mosquitoes more rapidly than they can breed. The fungi were engineered using a standard method employing a bacterium to transfer DNA into fungi. A control switch was also employed, anmely a gene that normally functions in inducing the fungus to build a defensive shell, a process that only occurs in certain environments such as in the bloodstream of mosquitoes.

Co-author, Raymond St. Leger (University of Maryland, MD, USA) explained: “These fungi are very selective. They know where they are from chemical signals and the shapes of features on an insect’s body. The strain we are working with likes mosquitoes. When this fungus detects that it is on a mosquito, it penetrates the mosquito’s cuticle and enters the insect. It won’t go to that trouble for other insects, so it’s quite safe for beneficial species such as honeybees.”

After demonstrating the safety of their genetically modified fungus in the lab the team moved to a test in a semi-field trial that simulated the natural environment.

In this screened-structure, the team reported that the expression of an insect-specific toxin (termed Hybrid) increased fungal lethality and the likelihood that insecticide-resistant mosquitoes would be eliminated from a site. Specifically, in the treated chambers the mosquito populations plummeted to just 13 adult mosquitoes after 45 days, compared with 455 mosquitoes in the wild-type fungi chamber and 1396 in the untreated chamber. Moreover, the researchers discovered that the Hybrid-expressing fungus had a longer efficacy than unmodified Metarhizium.

St. Leger commented: “We demonstrated that the efficacy of the transgenic fungi is so much better than the wild type that it justifies continued development.”

Brian Lovett (University of Maryland) commented: “No transgenic malaria control has come this far down the road toward actual field testing. This paper marks a big step and sets a precedent for this and other transgenic methods to move forward.”

The researchers suggest that deployment of transgenic Metarhizium against mosquitoes could be rapid as the fungus could be integrated with existing chemical control strategies.

Lovett concluded: “By following EPA and World Health Organization protocols very closely, working with the central and local government to meet their criteria and working with local communities to gain acceptance, we’ve broken through a barrier. Our results will have broad implications for any project proposing to scale up new, complex and potentially controversial technologies for malaria eradication.”

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Source: Lovett B, Bilgo E, Milogo SA et al. Transgenic Metarhizium rapidly kills mosquitoes in a malaria-endemic region of Burkina Faso. Science 364(6443), 894–897 (2019); https://cmns.umd.edu/news-events/features/4445

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