Entomological surveillance to assess potential outbreak of Aedes-borne arboviruses and insecticide resistance status of Aedes aegypti from Cape Coast, Ghana

Abstract

This study was conducted in Cape Coast, a major tourist destination in Ghana to assess the risk of an outbreak of Aedes-borne arboviruses based on entomological indicators and determine their susceptibility to pyrethroid insecticides. A larval survey was conducted in 414 houses between April and July 2017. Larvae collected were reared to adult for WHO susceptibility bioassay against four pyrethroid insecticides (Deltamethrin 0.05%, Permethrin 0.75%, Cyfluthrin 0.15%, Etofenprox 0.5%) and three different brands of mosquito coil; Heaven® (Dimefluthrin 0.03%), Sasso® (Esbiothrin 0.25%), and Fastkit® (D-allethrin 0.25%) as well as four enzyme-activities and F1534C kdr-mutation. Some physicochemical parameters were also measured in Aedes breeding sites. Three larval indices and water quality index (WQI) were calculated. The estimated larval indices were: House index – 68%, Container index – 44%, and Breteau index – 2.4. The level of resistance of the vector to the different pyrethroid insecticides and mosquito coils varied. F1534C kdr-mutation with an allele frequency of 35% and metabolic detoxifying enzyme activities are suspected to be the cause of resistance. Ae. aegypti breeding sites were found to contain organic and other anthropogenic pollutants. Based on the larval indices estimated, the population density of Ae. aegypti in Cape Coast was found to be sufficient to promote an outbreak of arboviruses. Pyrethroid resistance in the vector population could compromise the effectiveness of pyrethroid-based control strategies as was seen with the reduced efficacy of mosquito coils. With large number of international travellers to the city, there is a need to put in place a regular Aedes surveillance program for early response to any potential outbreaks.