New and potentially controversial techniques, including releasing genetically modified (GM) or irradiated mosquitoes, could be deployed to hamper the spread of the Zika virus, according to a statement from the WHO yesterday.
Zika is a disease transmitted by the Aedes aegypti mosquito. The disease originated in Africa, but in the last decade it has spread to French Polynesia in the South Pacific and to Brazil and Colombia in South America. More than 13 countries in the Americas have reported sporadic infections.
“Given the magnitude of the Zika crisis, WHO encourages affected countries and their partners to boost the use of both old and new approaches to mosquito control as the most immediate line of defense,” the WHO statement said.
It said more research was needed to evaluate the new techniques.
“For genetically modified mosquitoes, the WHO advisory group has recommended further field trials and risk assessment to evaluate the impact of this new tool on disease transmission,” the statement said, adding that trials in the Cayman Islands have shown significant reductions in the Aedes aegypti population there.
The disease is relatively mild, but infection in pregnant women has been linked repeatedly with a condition in babies called microcephaly and an illness in adults called Guillain-Barre syndrome.
“If these presumed associations are confirmed, the human and social consequences for the over 30 countries with recently-detected Zika outbreaks will be staggering,” the statement added.
Sprays and chemical assault remain standard tactics in the fight against insect-borne disease. However, Aedes aegypti is a serious problem: The mosquito carries both the malaria parasite and dengue fever, as well as Zika.
Before Christmas last year, a British House of Lords committee said that the UK had a “moral duty” to prosecute research on genetically modified insects and their use in disease control.
“We have a number of tools in our box and one of those that is being field-trialed at the moment for dengue is a GM mosquito, which is essentially to release mosquitoes so that when they mate, their offspring die in the larval stage,” said Michael Bonsall, a professor of mathematical biology at the University of Oxford and an adviser to the committee. “That has been tested in the field. It is exactly the same mosquito that spreads Zika. So it’s just a tool, it’s not the only thing we do, it is one of the things we do.”
Trials have shown that such releases could reduce an insect population by up to 90 percent, he said.
“But we know from disease theory that we don’t necessarily have to eradicate mosquitoes from an ecosystem to have an affect on disease dynamics. As long as we suppress the population and make it smaller, below a threshold, it will have a big impact on the disease burden,” Bonsall added.
Jo Lines, of the London School of Hygiene and Tropical Medicine, said: “This is an invasive species, so getting rid of these mosquitoes would, if anything, restore the natural ecology, not destroy it.”
The WHO calls mosquito control “the most immediate line of defense.”
Brazil is investigating more than 4,300 suspected cases of microcephaly and more than 460 have been confirmed. Zika infection has so far been identified in 41 of those cases.
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