Scientist develops website tool to track insecticide resistance

By Bernard Muthaka

A Kenya-based scientist has developed a website tool to track insecticide resistance.

The aggressive push for use of insecticide-treated nets and indoor spraying has resulted in considerable reduction in malaria cases, with experts reporting that over 700,000 lives were saved in 34 countries between 2001 and 2010.

Those gains are now at risk due to the rapid spread of insecticide resistance, which threatens to render the life-saving tools ineffective. In an effort to track the worrying trend, scientists from KEMRI/CDC and Vestergaard Frandsen have developed the world’s first Online mapping tool that will track insecticide resistance in mosquitoes.

IR Mapper

The interactive website, called IR Mapper, identifies locations in more than 50 malaria-endemic countries where mosquitoes have developed resistance to the insecticides used in bed nets and indoor residual sprays.

“Deployment of the most appropriate insecticide based vector control interventions including nets and IRS needs to be informed by up-to-date data on insecticide resistance in the malaria vector species,” says Dr Nabie Bayoh, an entomologist at KEMRI/CDC in Kisumu, Kenya.

Dr Bayoh says that prior to the development of the tool, insecticide resistance data has been scattered throughout different databases and has come from a variety of sources, making prompt decision-making difficult.

Earlier this year, the World Health Organisation (WHO) published fresh criteria for reporting insecticide resistance. The criteria, which are incorporated in the IR Mapper, are aimed at detecting resistance earlier. 

The tool provides comprehensive and up-to-date information on which vector control tools should be deployed in areas of high resistance. Resistance among Anopheles malaria vectors has been reported in 64 countries, with Sub-Saharan Africa being of greatest concern.

  Insecticide susceptibility

The aggregated IR Mapper gives data on insecticide susceptibility and resistance mechanisms from as far back as 1959 to 2012. To measure resistance, researchers put mosquitoes in a tube lined with insecticide-treated paper. If 80 per cent die as a result of absorbing the insecticide, it was considered that they are resistant.  The new guidelines by WHO have revised this threshold 90 per cent, meaning that resistance will be reported earlier.

With the new IR Mapper tool, users can examine the resistance status of single or multiple Anopheles species to one or more insecticides within their region of interest. It means countries can make independent decisions regarding the deployment of a particular insecticide.

Variations in deployment can also be made depending on specified time periods and the existing trends in resistance.

 The new tool responds to malaria control policy makers and researchers’ quest for a user-friendly approach to visualising and exploring up-to-date information on insecticide resistance. In most countries, pyrethroids are the insecticides of choice for malaria vector control.  This is because they are less toxic to mammals, have longer residual periods and are also less costly.  All approved long-lasting insecticidal nets use pyrethroids.

Their popularity though is also the biggest cause for the increasing problem of resistance to insecticides in malaria vectors. Two months ago, researchers reported that mosquitoes have developed variations that make them resist a compound known as DEET, which is used in most household mosquito repellents.

Mosquitoes have developed variants for resistance

Two months ago, researchers reported that mosquitoes have developed variations that make them resist a compound known as DEET, which is used in most household mosquito repellents.

They said that it takes only about three hours for the repellents to be rendered useless as the mosquitoes become insensitive to the smell. For years, DEET has been used in sprays, lotions, liquids and wristbands to repel insects. A slight exposure to DEET was reported to be enough to make some mosquitoes less sensitive to the repellent, meaning that three hours after exposure, the mosquitoes can go back to seeking out human skin to bite.

“We think that the mosquitoes are habituating to the repellent, similar to a phenomenon seen with the human sense of smell also,” adds one of the researchers.

In Africa, recent findings have suggested that the genetic structure of the Anopheles gambiae, which is responsible for most malaria cases in Africa, is evolving, explaining the difficulties in bringing the disease under control. The genetic changes are thought to be due to inter-mating between the species, resulting in hybrids that may bring about insecticide resistance and malaria parasite infectivity. The study that was released last month says that the inter-mating and subsequent hybrids were found in four countries in West Africa.