In a paper published in the March 31, 2019 issue of Science journal, a team of scientists from the University of Maryland (UMD) and Burkina Faso showed that naturally occurring fungi engineered to deliver a toxin to mosquitoes vanquished more than 99% of them in a screen-enclosed, simulated village setting in Burkina Faso, West Africa. If implemented well, it may be a maiden step to a Malaria free world by 2030.

According to the World Health Organization (WHO), 91 countries and territories had ongoing malaria transmission and an estimated 3.2 billion people – nearly half the world’s population – were at risk of malaria in 2016. Sadly, an estimated 216 million cases suffered from malaria that year and 4, 45,000 died due to malaria worldwide.

Malaria is no more confined to hilly and tribal areas. The life-threatening disease has reared its head in small cities and other urban areas as well. This writer recalls the anxiety and concern it caused a few years ago, when the Bhabha Atomic Research Centre (BARC) hospital started identifying many malaria infected patients in Anushaktinagar, where the residential quarters of the staff and officers of the Department of Atomic Energy are located.

Public health agencies worldwide have been using insecticides against mosquitoes that carry malaria parasite for the past several decades with little or no success. Insecticide-impregnated bed nets or indoor residual spraying on walls and ceilings are now ineffective as anopheline malaria vectors have gained sufficient resistance.

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Transgenic approach

Of late, scientists changed their strategy by genetically modifying mosquitoes and other organisms to eradicate their enemy. So far, the researchers confined these annihilation activities to laboratories.

Not anymore. The paper in Science describes the transgenic approach applied in simulated field conditions.

Earlier, the researchers applied Metarhizium spores inside traditional houses in Tanzania and found that the number of infectious bites reduced. However, it did not provide complete protection as the pathogen has low virulence, low persistence and needed high inoculum loads.

They engineered a strain of Metarhizium pingshaense (Mp-Hybrid) to express a US Environmental Protection Agency (EPA) approved, insect-specific toxin to remedy these deficiencies.

They demonstrated in lab studies that this toxin (Mp-Hybrid) is effective at very low spore doses, as low as a single spore per mosquito; it acted faster and its effectiveness lasted longer than that of the unmodified wild type Metarhizium.

"No transgenic malaria control has come this far down the road toward actual field testing," a press release from the UMD quoted Brian Lovett, a graduate student in UMD's Department of Entomology and the lead author of the paper.

"This paper marks a big step and sets a precedent for this and other transgenic methods to move forward.” he added

"We demonstrated that the efficacy of the transgenic fungi is so much better than the wild type that it justifies continued development," Raymond St. Leger, a Distinguished University Professor of Entomology at UMD and co-author of the study clarified

They conducted a trial in a semi-field facility (MosquitoSphere) near a rural village in a region of Burkina Faso where malaria is endemic.

Etienne Bilgo, a co-author of the paper observes one of the breeding pools in MosquitoSphere where researchers found that the simple application of a transgenic fungus on a hanging black sheet safely reduced mosquito populations by more than 99%. CREDIT: Oliver Zida

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The fungus is a naturally occurring pathogen that infects insects in the wild; however, it kills them slowly. People have used it to control various pests for centuries. The strategy developed by the scientists was to use a strain of the fungus that is specific to mosquitoes and to engineer it to produce a toxin that kills mosquitoes more rapidly than they can breed. This GM fungus caused mosquito populations in their test site to collapse to unsustainable levels within two generations.

Professor St Leger rightly characterised the fungus as a “hypodermic needle which delivers a potent insect-specific toxin into the mosquito”.

The toxin is an insecticide called Hybrid, derived from the venom of the Australian Blue Mountains funnel-web spider. The Environmental Protection Agency (EPA) has approved it for application directly on crops to control agricultural insect pests.

Lovett revealed that they simply applied the transgenic fungus to a sheet and hung it on a wall in the study area. It caused the mosquito populations to crash within 45 days.

"And it is as effective at killing insecticide-resistant mosquitoes as non-resistant ones.” he asserted

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To modify the fungus Metarhizium pingshaense so that it would produce and deliver Hybrid, the research team used a standard method that employs a bacterium to intentionally transfer DNA into fungi. The DNA, the scientists designed and introduced into the fungi provided the blueprints for making Hybrid and a control switch that tells the fungus when to make the toxin.

“The control switch is a copy of the fungus' own DNA code. Its normal function is to tell the fungus when to build a defensive shell around itself so that it can hide from an insect's immune system. Building that shell is costly for the fungus, so it only makes the effort when it detects the proper surroundings--inside the bloodstream of a mosquito” the press release explained.

By combining the genetic code for that switch with the code for making Hybrid, the scientists could ensure that their modified fungus only produces the toxin inside the body of a mosquito. They tested the modified fungus on other insects in Maryland and Burkina Faso, and showed that it was not harmful to beneficial species such as honeybees. If the fungus killed honeybees, the collateral damage would have been unacceptable.

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." he explained

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Simulated field

In a rural, malaria-endemic area of Burkina Faso, the researchers constructed a roughly 6,550-square-foot, screened-in structure which they called MosquitoSphere. Inside, multiple screened chambers contained experimental huts, plants, small mosquito-breeding pools and a food source ( calves in the hut for blood meals) for the mosquitoes.

In one set of experiments, the researchers hung a black cotton sheet coated with sesame oil on the wall of a hut in each of three chambers. One sheet received oil mixed with the transgenic fungus Metarhizium pingshaense, one received oil with wild-type Metarhizium and one received only sesame oil. Then, they released 1,000 adult male and 500 adult female mosquitoes into each chamber of MosquitoSphere to establish breeding populations. The researchers then counted mosquitoes in each chamber every day for 45 days.

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According to the researchers, it is critically important that new anti-malarial technologies are easy for local communities to employ. Black cotton sheets and sesame oil are relatively inexpensive and readily available locally. The practice also does not require people to change their behaviour, because the fungus can be applied in conjunction with pesticides that are commonly used today.

"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," Lovett said. "Our results will have broad implications for any project proposing to scale up new, complex and potentially controversial technologies for malaria eradication." These scientists hope to test shortly their transgenic fungus in a local village or community.

On April 24, 2019 the Indian Council of Medical Research while launching Malaria Elimination Research Alliance (MERA) noted the impressive progress in India’s Malaria control programme. All stakeholders must remain eternally vigilant to maintain the progress and to achieve greater goals.

Dr. K S Parthasarathy is a freelance science journalist and a former Secretary of the Atomic Energy Regulatory Board. He is available at ksparth@yahoo.co.uk