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University of Liverpool (2015)

Characterisation of insecticide resistance in Anopheles gambiae from Burkina Faso and its impact on current malaria control strategies

Toe, Hyacinthe

Titre : Characterisation of insecticide resistance in Anopheles gambiae from Burkina Faso and its impact on current malaria control strategies.

Auteur : Toe, Hyacinthe

Université de soutenance : University of Liverpool

Grade : Doctor of Philosophy (PhD) 2015

Résumé
Malaria is the primary cause of death in Burkina Faso and affects mostly pregnant women and children under five years old. The control of Anopheles mosquitoes responsible for the transmission of the disease by universal coverage with long lasting insecticide treated bednets (LLINS) is one of the keys strategies adopted by many malaria endemic countries. Pyrethroids remain the only insecticide class approved to be used on nets. The proportion of mosquitoes resistant to this insecticide class has steadily increased since its first report in the rice fields of Vallée du Kou in 1999 and it is now rare to find any mosquitoes from this region of Burkina Faso surviving standard WHO susceptibility diagnostic dose assays. However, without data on the magnitude of resistance it is difficult to predict the impact that this may have on malaria vector control. This study assessed the strength of the pyrethroid resistance and the underlying mechanisms, before determining whether LLINs adequately kill wild resistant mosquitoes using both newly acquired LLINs and nets previously used by householders. Mosquitoes collected in the rice field of Vallée du Kou from 2011 to 2013 were tested against the four insecticides classes approved in public health. The time taken to obtain 50 % mortality (LT50) using 0.05% WHO deltamethrin papers was determined in 2011 and 2012 while CDC bottle bioassays were used to establish the concentration of deltamethrin needed to achieve 50 % morality (LC50) in 2013. The data confirmed the high prevalence of resistance to DDT and pyrethroid in Anopheles gambiae s.l from Vallée du Kou. The LT50 increased from 98 mins to 1315 mins in just one year, representing an increase > 10 fold while the LC50 recorded in 2013 exceed 1000 fold compared to laboratory susceptible Kisumu strain Anopheles gambiae s.l populations from the bioassays were screened for target site mutations in the sodium channel. The dramatic increase in the strength of resistance was not accompanied by an increase in genes frequency, as the frequencies of the 1014F and 1575Y mutations remained stable at approximately 0.8 and 0.3 respectively in the three years. Microarray was used to identify alternative candidate genes associated with the increasing level of resistance to pyrethroids. Quantitative PCR was used to demonstrate that a subset of these candidate genes, including P450s, GSTs, CCEs, aquaporin and chymotrypsin increased significantly between 2011 and 2013 and may be contributing to the increase in resistance observed recently in this study site The bio-efficacy of used and new LLINs of six different brands, distributed as part of the National Control Malaria Program (NMCP) of Burkina Faso was assessed using cone bioassays. Whilst some of the nets gave acceptable levels of mortality against the laboratory susceptible Kisumu strain, none were able to kill more than 45 % of the resistant wild mosquitoes from Vallée du Kou. These results demonstrate that the high levels of resistance in An. gambiae s.l in Burkina Faso is having a real impact on the ability of LLINs to kill mosquitoes which will have serious implications for malaria control in this region

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Page publiée le 27 novembre 2015, mise à jour le 10 novembre 2019