Zika Update: Mosquitoes Developing Resistance to Insecticide

By Bri Ziganti

The CDC has confirmed that Zika-spreading mosquitoes have begun developing a resistance to insecticide; specifically, the world’s top mosquito repellent.  This compound, called permethrin, was once hailed as a safer, more environmentally-friendly, yet still effective alternative to harsher chemicals.  Now, however, it seems permethrin has outlived its usefulness.

Roberto Barrera, chief of entomology and ecology activity of the Dengue Branch at the CDC, says he’s received reports of resistance in both Puerto Rico and parts of Mexico.

“[Permethrin] probably won’t work well in the places where it has been used as the main insecticide for many years.  You’re not going to be able to kill off most of the mosquitoes,” Barrera said.

This is especially bad news for areas where Zika has already spread fast and fierce.  Traditionally, mosquito nets are one of the simplest, cheapest, and cost-effective ways to protect against mosquitoes.  Many people will treat their nets with a coating of permethrin to kill any insects before they can find holes in the netting.  Some will even treat their clothing for additional protection during the day, as one good spray-down can last through several washes.  Now that Aedes mosquitoes are showing a resistance to insecticide, prevention has become that much more difficult.

What is Permethrin and Why is Resistance to Insecticide a Problem?

zika-spreading mosquitoes developing resistance to insecticidePermethrin is a neurotoxin that is deadly to mosquitoes but harmless towards humans and most mammals, with the exception of cats.  The insecticide isn’t easily absorbable by our skin, making it a great nontoxic barrier that prevents mosquitos from biting.

While insecticides are viewed with suspicion by some, permethrin is one of the few pest repellents on the market to command a large amount of public approval.  It is currently one of the most commonly used repellents worldwide.

Since there is no Zika vaccine, eliminating breeding grounds and killing adult mosquitoes before they have a chance to bite is the best and only strategy authorities are able to implement today.  A vaccine may yet be developed, but testing will take time.  News of insecticide resistance is a serious blow to heavily affected countries.

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