When it comes to fighting malaria, researchers not only need to stop the killer cold in its tracks, but they also have to ensure their solutions harm only disease-carrying mosquitos and not the rest of the environment. A new turbocharged fungus out of the University of Maryland promises to do exactly that.
The fungus, Metarhizium pingshaensei is a natural killer of disease-carrying mosquitoes including Anopheles gambiae and Aedes aegypti.
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"The fungus infects the insect via spores," Brian Lovett, a graduate student in the UMD Department of Entomology and a co-author of the paper told New Atlas. "A spore lands on the insect surface, and if the chemistry and topography of the cuticle is suitable for the fungus, it will germinate and produce a short germ tube which swells to produce an infection structure. The infection structure of the fungus then grows down into and through the cuticle into the insect blood. Here, the fungus then changes form and buds off in a yeast-like single celled stage that disperses through the insect."
In nature though, it takes a good amount of spores to bring down a mosquito. So the UM researchers, along with colleagues from Burkina Faso, China and Australia, genetically engineered the fungus to express toxins from the North African desert scorpion and another derived from the Australian Blue Mountains funnel-web spider.
The resultant "super fungus" was strong enough to kill a mosquito with just one spore. What's more, the fungus is naturally spreadable.
"Once the insect is killed, the fungus grows out through the cadaver's cuticle and produces spores on the insect surface which is then available to infect the next generation of insects," Lovett told us.
The altered fungus works because the scorpion toxin blocks sodium chemical channels in the bug, while the toxin from the spider shuts down potassium and calcium channels. In tests, the fungus also stopped mosquitos from feeding on blood. Oh, and the spores were also designed to give off a green fluorescent protein, so that researchers could track the efficacy of their approach.
Lovett said that between the fungi's ability to kill mosquitos and stop them from feeding, they were able to prevent transmission of malaria by 90 percent in five day.
Perhaps more impressively though, the engineers created the spores to only express the toxins once they were inside the blood of the mosquito, so that there was no chance of them leaking out into the environment. Further, they also showed that the fungus was safe to honey bees by both exposing the bees to fabric coated with the fungus and by spraying them with a liquid spore solution. Two weeks later, no bees had died. Similarly, the fungus had no effect on insects closely related to mosquitoes such as gnats and midges.
"The toxins we're using are potent, but totally specific to insects," said Raymond St. Leger, a professor in the UMD department of entomology and senior author of the study, in a statement. "They are only expressed by the fungus when in an insect. Additionally, the fungus does nothing at all to bees and other beneficial species. So we have several different layers of biosecurity at work."
In tests, the toxin-enriched fungus was effective in killing even insecticide-resistant mosquitoes.
"The WHO has identified insecticide resistance as the major threat to effective mosquito control, which is relevant not only to malaria but to a number of mosquito-borne diseases such as dengue, yellow fever, viral encephalitis and filariasis," said St. Leger. "Unlike chemical insecticides that target only sodium channels, many spider and scorpion toxins hit the nervous system's calcium and potassium ion channels, so insects have no pre-existing resistance."
The next step for the researchers is to expand their testing in Burkina Faso where they are currently using a custom-built enclosure to conduct their research. Their hope is to deploy the spores in the field on wild mosquitoes. Should that effective, the toxic fungus could join other malaria-fighting measures including using a synthetic synthetic protein to cure infected humans; using a vaccine to prevent infection in the first place; and genetically modifying mosquitoes to develop resistance to the malaria parasite (and to have glowing eyes!).
The work of the researchers has been published in the journal Scientific Reports.