- Researchers use designer-mosquitoes to curb lethal diseases
- With no vaccine, avoiding bites is best way to prevent Zika
Scott Ritchie spent decades “spraying and slaying” mosquitoes. Then he realized that the best way to defeat the blood-suckers was to breed more of them.
Ritchie, a medical entomologist, is now involved in rearing and releasing mosquitoes around the Australian city of Cairns, where he lives. These insects though, are infected with a naturally occurring bacterium called Wolbachia, which inhibits their ability to spread deadly dengue and potentially Zika.
Zika, the viral disease spreading “explosively” in Latin America, has highlighted how decades of efforts to eradicate diseases spread by mosquitoes have failed. With no vaccine or cure for Zika, the most effective protective strategies involve controlling mosquitoes and avoiding their bites, the World Health Organization said on Monday.
After years of attacking mosquito communities with chemicals such as DDT, research has shifted to new experimental approaches based on the habits and life cycle of the pests. These include releasing into the wild sterile male and genetically modified mosquitoes designed to decimate populations of the disease-spreaders.
“We have spent millions of dollars killing mosquitoes,” said Ritchie, a researcher with the Centre for Biosecurity in Tropical Infectious Diseases at James Cook University, who began working in mosquito control in 1976. “Now, we’re spending millions of dollars rearing and releasing them. I find that ironic.”
While the malaria-carrying Anopheles mosquito is the world’s deadliest insect, killing more than 480,000 people annually, it’s the Zika-spreading Aedes aegypti species that’s currently garnering worldwide attention. Originally from Africa, the people-loving arthropod is now distributed globally in tropical and subtropical regions, where it can spread not only Zika virus, but also deadly diseases like yellow fever and dengue.
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Here’s an overview of some of the currently used and experimental approaches targeting mosquitoes and the diseases they spread:
FOGGING disperses pesticide in a thick cloud of gas that will kill mosquitoes susceptible to the chemical in a confined space. It’s becoming a less effective strategy because of growing resistance worldwide to the synthetic pyrethroid chemicals that are mostly used.
SPATIAL REPELLENTS using chemical-impregnated materials that slowly release vaporized pesticides such as Sumitomo Chemical Co.’s metofluthrin are being studied as possible tools to deter mosquito bites in small spaces, such as a bedroom.
WOLBACHIA is a naturally occurring bacterium that researchers, funded by the Bill & Melinda Gates Foundation, are using to infect Aedes aegypti mosquitoes. Wolbachia has been shown in experiments to block transmission of dengue and may also stop the spread of Zika and other mosquito-borne viruses.
GENETIC-MODIFICATION of male Aedes aegypti mosquitoes by Intrexon Corp.’s Oxitec unit has been shown to cause the premature death of offspring -- preventing a new crop of mosquitoes from reproducing and spreading disease. Oxitec’s gene-modified mosquito was approved by Brazil’s biosecurity commission in April 2014 and is awaiting final clearance from the Ministry of Health to authorize the sale of the mosquitoes to local authorities and private operators.
GENE-EDITING is being explored at London’s Imperial College and the University of Washington, Seattle, as a way of tweaking the genetic makeup of mosquitoes. Researchers are investigating whether genetic changes can be introduced into a mosquito population that could prevent the insects from transmitting pathogens, such as malaria.
STERILIZING male mosquitoes by exposing them to specific RNA molecules during the larvae stage has been shown to reduce insect populations in experiments. Further studies, funded by Australia’s National Health and Medical Research Council, are underway.