Studies on Insecticides Usage Pyrethroid Resistance in Populations of ANOPHELES GAMBIAE SENSU STRICTO in The Greater Accra Region

ABSTRACT

Insecticide resistance due to knockdown resistance (kdr) mutations in Anopheles gambiae populations has been reported in neighbouring West African countries, such as Cote d’Ivoire, Burkina Faso and Benin despite the absence of large-scale mosquito control in these countries. The hypothesis is that agricultural or household use of insecticides is responsible for the evolution of resistance. However, studies relating such uses of insecticides and the development of resistance in An. gambiae have not been carried out in Ghana. Meanwhile, Ghana is one of the countries where insecticide treated bednets is a major component of the Roll Back Malaria programme. Pyrethroid insecticide resistance could hamper this mass control effort; hence there is the need teFestablish baseline information on insecticide use pattern and vector susceptibility levels for this country. To achieve these objectives a questionnaire survey was conducted to obtain information on the household insecticide usage and habits in the Accra Metropolis. Then adult An. gambiae reared- from larvae collected at geopositioned sites were tested at diagnostic doses of permethrin (0.75%) and deltamethrin (0.05%) using WHO adult mosquito test kit to assess the impact of insecticide usage on levels of resistance. The presence of gene mutations associated with knockdown resistance [kdr) in the test mosquitoes was detected using polymerase chain reaction (PCR) with already published oligonucleotide primers Agd1, Agd2, Agd3 and Agd4. Polymerase chain reaction was also used to identify the species of the An. gambiae complex. A total of 171 households were surveyed. Results of this survey revealed that the frequency of pyrethroid insecticide application was high. Most XV respondents said the available aerosols were not as effective as they expected. However, respondents still preferred aerosols to coils and that the aerosol of choice was RAID* which contains tetramethrin (0.15%), allerthrin (0.25%), and deltamethrin (0.015%). There was no significant difference between the reported incidences of malaria in all the socio-economic classes of the respondents. All bioassays showed mortalities ranging from 68-88% (mean: 78%) indicating the existence of resistance in An. gambiae populations in Accra. The specimens identified by PCR were all An. gambiae s.s. and kdr mutations were found in 52/195 (26.7%) of the sample population and 39/48 (81.3%), thus colloborating the results of the bioassay. The importance of this study, being the first of its kind in Ghana, was to obtain baseline data essential for monitoring resistance in An. gambiae s.I for future malaria vector control and the implications of findings in the context of malaria control in Ghana are discussed in Chapter five.