Research
Insecticide resistance in Anopheles gambiae: data from the first year of a multi-country study highlight the extent of the problem
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* Corresponding author: Hilary Ranson hranson@liv.ac.uk
1 Vector Group, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
2 Vector Biology & Control unit, Blue Nile National Institute for Communicable Disease, PO Box 101, Wad Medani, Sudan
3 Centre National de Recherche et de Formation sur le Paludisme 01 BP 2208 Ouagadougou 01, Burkina Faso
4 Université de Ouagadougou, BP 7021, Ouagadougou 03, Burkina Faso
5 National Malaria Control Programme BP 1043, N'Djaména, Chad
6 Institut de Recherche pour le Développement (IRD), UR016 and Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 171 Bobo-Dioulasso, Burkina Faso
7 Malaria Entomology Research Unit, School of Pathology, University of the Witwatersrand, Johannesburg 2000, South Africa
8 Vector Control Reference Unit, National Institute for Communicable Diseases of the NHLS, Private Bag X4, Sandringham, Johannesburg 2131, South Africa
Malaria Journal 2009, 8:299 doi:10.1186/1475-2875-8-299
Published: 17 December 2009Abstract
Background
Insecticide resistance in malaria vectors is a growing concern in many countries which requires immediate attention because of the limited chemical arsenal available for vector control. The current extent and distribution of this resistance in many parts of the continent is unknown and yet such information is essential for the planning of effective malaria control interventions.
Methods
In 2008, a network was established, with financial support from WHO/TDR, to investigate the extent of insecticide resistance in malaria vectors in five African countries. Here, the results of bioassays on Anopheles gambiae sensu lato from two rounds of monitoring from 12 sentinel sites in three of the partner countries are reported.
Results
Resistance is very heterogeneous even over relatively small distances. Furthermore, in some sites, large differences in mortality rates were observed during the course of the malaria transmission season. Using WHO diagnostic doses, all populations from Burkina Faso and Chad and two of the four populations from Sudan were classified as resistant to permethrin and/or deltamethrin. Very high frequencies of DDT resistance were found in urban areas in Burkina Faso and Sudan and in a cotton-growing district in Chad. In areas where both An. gambiae s.s. and Anopheles arabiensis were present, resistance was found in both species, although generally at a higher frequency in An gambiae s.s. Anopheles gambiae s.l. remains largely susceptible to the organophosphate fenitrothion and the carbamate bendiocarb in the majority of the sentinel sites with the exception of two sites in Burkina Faso. In the cotton-growing region of Soumousso in Burkina Faso, the vector population is resistant to all four classes of insecticide available for malaria control.
Conclusions
Possible factors influencing the frequency of resistant individuals observed in the sentinel sites are discussed. The results of this study highlight the importance of standardized longitudinal insecticide resistance monitoring and the urgent need for studies to monitor the impact of this resistance on malaria vector control activities.