Malaria-carrying Mosquitoes Becoming Resistant to Bed Nets in Southern Africa

Malaria-carrying mosquitoes are becoming resistant to the insecticide used in bed nets to prevent the disease. Researchers say it is important to stay ahead of the resistance to avoid what they are calling a public health catastrophe.

An Anopheles stephensi mosquito. Image credit: Jim Gathany/PHIL/Wikipedia (PD)

Bed nets treated with inexpensive pyrethroid insecticides are the main defense against biting, malaria-carrying mosquitoes, and they have significantly cut down on the number of cases. The World Health Organization reports malaria infected an estimated 212 million people in 2015, killing some 429,000 of them.

That reflects a 21 percent drop in the incidence of between 2010 and 2015.

But a new study, published in the journal PLoS Genetics, found that the primary mosquito that harbors the parasite in southern Africa, Anopheles funestus, is rapidly becoming resistant to the insecticide. In at least one country, Mozambique, researchers discovered that 100 percent of A. funestus remained alive after direct exposure to the chemical.

Charles Wondji, a mosquito geneticist at the School of Tropical Medicine in Liverpool, England, notes that resistance to pyrethroid insecticides occurred rapidly, in about eight years.

Wondji said scientists were able to identify the resistance gene in the mosquito. Speaking with VOA from Cameroon, he said that will give scientists an important tool to monitor the spread of insect resistance throughout the continent.

“That form of the gene is now very prevalent in southern Africa with the risk that if we do nothing there's a chance that those control measures won't work against those type of mosquitoes,” he said.

By having identified the responsible gene, Wondji said it will be possible to stay ahead of what he calls the “resistance curve” in places where insecticides are starting to fail to kill the mosquitoes. He added other more expensive insecticides can then be deployed to treat the bed nets. He mentioned a compound called PDO that targets the gene, killing the mosquitoes.

Wondji said control efforts, such as eliminating mosquito larvae that inhabit standing pools of water, can also be redoubled.

Wondji noted other species of malaria-carrying mosquitoes, like Anopheles gambiae, are starting to become resistant to pyrethriods, although that is occurring through a different biological mechanism.

Therefore, Wondji, said it's important to study all species of malaria-carrying mosquitoes in order to implement appropriate and successful malaria management strategies.

In another just-released study in the journal The Lancet Infectious Diseases, scientists in Thailand have found widespread malaria parasite resistance to artemisinin and combination therapies using artemisinin, considered the gold standard treatment.

They say the development threatens global malaria control and eradication efforts. (VOA)

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