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Insecticide resistance in African malaria vectors: protocols and results from a TDR sponsored network

Source: TropIKA

A network of scientists is determining the extent of current levels of insecticide resistance in malaria vectors and the mechanism of development of resistance by these vectors.

Author: Paul Chinnock

Reports of resistance to insecticides used in malaria control have caused much concern, particularly with regard to resistance to the pyrethroids used in insecticide-treated bednets. While there have been many individual reports, no structured information has been gathered as to how common and widespread resistance actually is. In many African countries no data has yet been collected.

TDR has established a network ­– led by Dr Hilary Ranson at the Liverpool School of Tropical Medicine, UK working with partners in six African countries – to develop standardised protocols for vector population monitoring, and for determining the levels of insecticide susceptibility in sentinel sites in each country. In addition more detailed research will be conducted into resistance mechanisms.  The results and recommendations of the study will be used to inform malaria control programmes and promote sustainable insecticide based interventions.

The network was launched in June 2008 and good progress has already been made in three countries – Burkina Faso, Chad and Sudan. Activities have also begun in Angola and Benin.

Speaking to TropIKA.net in advance of her presentation at the MIM conference, Dr Ranson said that “alarmingly high” levels of resistance had been found in the research so far conducted in this project. She explained that research into the molecular causes of this resistance would be an important activity for the network as it would facilitate efforts to follow the development of resistance.

Longitudinal monitoring of resistance is an important component of the network’s activities. It has been shown that resistance levels fluctuate during the transmission season, generally rising as it progresses. Further work will be required to determine whether resistance is actually increasing year on year.

One vector species that has been little studied is Anopheles arabiensis, even though it plays an important role in malaria transmission in many areas. Dr Ranson said the species would be considered an important part of the project.

Researchers in the network will also seek to determine the impact of the development of resistance. Are resistant mosquitoes still deterred from biting? Or does resistance result in increased bite rates and increased transmission of malaria?

The network’s activities will not be confined to pyrethroid resistance. The other three groups of insecticide used in vector control – DDT, organophosphates and carbamates are also part of the project.

Bursaries are being provided to African researchers to enable them to study resistance mechanisms. Some of the researchers will come to the Liverpool School in order to so; some will go to institutions in other African countries.

The network will collaborate with other projects that are gathering data on insecticide resistance in malaria vectors. Dr Ranson is looking forward to the MIM conference, where she hopes there will be an opportunity to discuss the work of the network with other scientists engaged in this key area of malaria research. She is looking forward to feedback on her presentation.

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