Baseline Susceptibility Of Malaria Vectors To Clothianidin In The Northern Region Of Ghana

Abstract

The emergence and spread of insecticide resistance coupled with the widespread distribution of malaria vectors in Ghana makes malaria control a cumbersome task. Currently in Ghana and most of the West African countries, malaria vectors have developed resistance to all four (4) classes of insecticides. Therefore, a new insecticide, clothianidin, which has a different mode of action, has been deployed for Indoor Residual spraying (IRS) in Ghana since March 2021. A detailed understanding of current phenotypic susceptibility to clothianidin used for IRS and the effect of this on mosquito mortality, as well as underlining resistance mechanisms is vital to inform management strategies. The aim of this study was to document the sub lethal effects of clothianidin on malaria vector susceptibility and longevity. This was a cross-sectional study. WHO susceptibility bioassays were conducted to determine phenotypic susceptibility of Anopheles gambiae complex to clothianidin whilst cone bioassays were conducted to determine the effect of exposure on mosquito mortality. Conventional PCR was done to discriminate the sibling species of the Anopheles gambiae complex and also to detect target-site mutations. WHO susceptibility bioassay results showed significantly effective but prolonged mortality of mosquitoes. Mortality rates recorded with the insecticide demonstrated a delayed effect with optimum mortality requiring up to 144hrs, six (6) days. The mortality rate for wild Anopheles mosquitoes exposed in WHO cone bioassays for 5-min, 24hrs after was 63%, showing resistance. Mortality increased to 97% after 120hrs, indicating possible resistance but after 144hrs, mortality of 100% was reached indicative of vector susceptibility. Mosquitoes exposed for 10-min had a mortality of 72% after 24hrs.This increased to 97% after 96hrs indicating possible resistance, but 120hrs was taken to reach full susceptibility of 100%. After 24hrs, mosquitoes exposed for 20-min reached 82% mortality, which increased to 97% after 96hrs indicative of possible resistance, this increased slightly to 98% after 120hrs showing susceptibility. A 95% mortality was reached for mosquitoes exposed for 30-min after 24hrs, thus giving an indication of suspected resistance, however, after 48hrs mortality reached was 98% suggesting susceptibility The PCR results revealed that Anopheles gambiae s. was the most abundant malaria vector accounting for 63% followed by Anopheles coluzzii also accounting for 25%, with Anopheles arabiensis accounting for 9% of the samples. There was high allele frequency of Kdr west (L1014F) in all vector species identified (0.89-0.94) with Ace-1 occurring in moderation (0.32-0.44). In this study, it was found that malaria vectors were susceptible to clothianidin. There were also a lot of resistant mutations in wild Anopheles mosquitoes. The most abundant malaria vector species was Anopheles gambiae s.s. Continued surveillance for susceptibility of malaria vectors to clothianidin should be conducted yearly to monitor possible resistance.