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Resistance to Insecticide Treated Nets: Why Are Mosquitoes Getting ‘’Smarter’’?

Mosquitoes have been observed to repeatedly adapt to newer forms of insecticides. Recent reports suggests that current measures seem to been losing its grip on controlling mosquitoes which appear to be getting ‘’smarter’’ over time.

According to a new study published June 18, PLoS Neglected Tropical Diseases, one of the most common insecticides used in the battle against the Aedes aegypti mosquito now has no impact in some communities in Mexico. The Aedes aegypti mosquito is responsible for the spread of Zika, Dengue and Yellow fever-all deadly diseases.

About 10 years ago, insecticides treated bed nets became a massive tool in the battle against mosquitoes in Africa. Pyretheroids which are affordable, odourless, cheap, long-lasting insecticides  became the most important agent in reducing the burden of malaria. In Nigeria alone, over 180 million nets impregnated with pyretheroids were deployed to ‘’roll back’’malaria.

Sadly, a  recent study published by Nigeria Institute of Malaria Research (NIMR) has suggested that insecticide treated nets are no longer very effective in several states. According to the lead author, Dr Awolola, resistance to insecticide treated nets was found in Jigawa, Katsina, Kebbi, Sokoto, Zamfara, Benue, Kwara, Nasarawa, Niger, Plateau, Anambra, Enugu, Rivers, Lagos, Ogun, Ondo, Osun and Oyo states.

This finding has been supported by some anecdotal reports. For instance, some have observed that mosquitoes now bite individuals through the nets or crawl under insecticide treated bed nets without getting killed.

This is a source of concern. In 2015, 212 million were infected with mosquito borne malaria. This led to the death of  429000  according to the World Health Organization.

Why is resistance to insecticides on the rise?

Excessive use of insecticides- According to Dr Sam Awolola of NIMR “Most of the insecticide products used in  malaria control are also being used in agricultural sector in Nigeria. This over-saturation is a major source of resistance.” The short life cycle of mosquitoes make it easily for them to avoid such insecticides or build up resistance to them.

Mutation-According to Dr Vazquez-Prokopec of Emory University,  ‘’It’s a natural biological process for mosquitoes to mutate in response to insecticide exposure, says. These mutations can occur at the molecular level, preventing the insecticide from binding to an enzymatic target site. They can also happen at the metabolic level — when a mosquito’s metabolism “up regulates” the production of enzymes that can neutralize the toxic effects of an insecticide.’’ In another related study, the researchers found that a single genetic mutation causes resistance to DDT and pyrethroids. These changes result in:

  • Insecticides is prevented from acting on the target areas within the mosquito
  • Increase rate of excretion of insecticides
  • Decrease rate of absorption of insecticide

Is there an end in sight?

“We’re always going to be chasing the problem of insecticide resistance in mosquitoes, but the more data that we have — and the more tools we have in our arsenal — the more time we can buy,” Vazquez-Prokopec says.

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