Analysis of insecticide resistance in populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidea), known as vectors of arboviruses in Cameroon
The objective assigned to this work was to assess the resistance to insecticides of populations of Aedes aegypti and Aedes albopictus, arboviruses vectors in Cameroon.
Dr. Aurelie Yougang collecting mosquito larvae
The results of this four years study, conducted as part of Dr. Aurelie Yougang’s doctoral thesis, show that the resistance profile of Aedes aegypti and Aedes albopictus varies considerably depending on the insecticides, the species and the origin of the samples tested. Generally, adult bioassays revealed resistance to permethrin 0.25%, deltamethrin 0.05%, bendiocarb 0.1%, propoxur 0.1% and DDT 4% in both species. However, full sensitivity was observed in all samples tested to fenitrothion. On the other hand, partial or complete restoration of resistance after pre-exposure of mosquitoes to the synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) suggests the involvement of cytochrome P450 monooxygenases and glutathione-s-s transferases in metabolic resistance of these samples. The CYP6P12 gene was found to be significantly overexpressed in samples of Ae. albopictus from Bertoua and Bafang. Contrary to Ae. Aegypti, none of the genes tested were significantly expressed. Nevertheless, the F1534C mutation was detected in populations of Ae. aegypti from Edea and Douala. The low frequency of this mutation suggests a recent introduction of this mutation into the population of Ae. aegypti from Cameroon.
Insecticide resistance being a dynamic phenomenon likely to vary over time. It would be important to continue assessing the susceptibility status of arbovirus vectors to insecticides over time to detect any changes. In addition, the variation of the resistance profile according to the localities provides highlights the need to implement a national arbovirus vector control program that takes into consideration the specificity of each locality. The localized distribution of the kdr F1534C mutation supports this region-specific control strategy.
Notice to public authorities and researchers
At the end of this work, based on the evidence obtained, Dr Aurelie Yougang, calls on the public authorities to set up surveillance and control programs for arbovirus vectors. Such programs should include actions aimed at improving water supply systems, environmental sanitation and health education. In the context of an epidemic emergency, the use of insecticides taking into account the specificities of each locality.
In addition, since the effectiveness of insecticides can be limited by the appearance of resistance phenomena, it is important to set up long-term monitoring and control tools to manage resistance.
The candidate during and after the defense
A rigorous scientific approach
To achieve the objectives of this study, we started by evaluating the resistance profile to different classes of insecticides of different populations of Ae. aegypti and Ae. albopictus from Cameroon. Following this, we looked for the mechanisms involved in metabolic resistance to insecticides and finally, we investigated the resistance mechanisms involved in resistance to insecticides by target modification. Since the beginning of the 20th century, vector-borne diseases have been at the forefront, because they are the first cause of death among infectious diseases. Of all arthropod vectors, mosquitoes are so far the most concerned and the most dangerous, because they are vectors of many pathogens like arboviruses such as yellow fever, dengue, chikungunya, zika, etc.
Due to the current lack of vaccines and specific drugs against most of these arbovirus infections, the only way to prevent epidemics is through vector control. This struggle is essentially based on the destruction of breeding sites and the use of insecticides, in particular larvicides against immature and adulticidal stages in emergency situations. However, the work carried out in different countries around the world has shown that vector populations are resistant to all families of known insecticides with varying levels from one country to another. With the emergence of Aedes resistance to all classes of insecticides used in public.
