ASSESSMENT OF THE BACTERIAL PROFILE OF LARVAL AND ADULT ANOPHELINES IN SOUTH-WEST NIGERIA AND IMPLICATIONS FOR PERMETHRIN RESISTANCE

Abstract

Malaria remains one of the major scourges and a contributor to morbidity and mortality in Nigeria. Despite efforts made by the National Malaria Elimination Program and its partners to control malaria, malaria still remains a major public health issue in Nigeria. Data from sentinel sites indicate that mosquitoes are now resistant to major classes of insecticides, necessitating a deeper understanding of vector dynamics. This study investigated the physicochemical parameters, heavy metal concentrations, algal toxin composition, and characterised the bacterial communities associated with mosquito larvae and permethrin-resistant and susceptible adult Anopheles mosquitoes collected from urban and rural communities in Ogun and Oyo States, Nigeria, between July and December 2024. The spatial distribution of the breeding sites was georeferenced, and the physicochemical parameters were measured in accordance with the American Public Health Association (APHA) standard protocols. The bacterial communities in the water samples, larvae, resistant, and susceptible adult mosquitoes were profiled using 16S rRNA PacBio sequencing, and functional metagenomics was performed with PICRUST2. Anopheles mosquitoes were identified using morphological keys and molecular characterisation by PCR techniques, and permethrin susceptibility was carried out following the WHO standard procedures. One hundred and twenty breeding sites were sampled, and six types of breeding sites were identified. Across the breeding sites, puddles had the highest occurrence of mosquito larvae habitats (56.7%), construction sites containers (15.8%), Tyres (13.3%), Drains (6.7%), Bowls (5.8%), and Wells (1.7%). Physicochemical parameters, such as Chemical Oxygen Demand, Temperature, and pH, were high at breeding sites with no larvae presence in urban and rural areas across Oyo and Ogun states. Larvae presence was identified in breeding sites with algal toxins, and the presence of saxitoxins influenced the presence of larvae. The bacterial composition of the water samples was 80% Gramnegative and 20% Gram-positive with four most abundant taxa which include the Pseudomonas 22%, Aeromonas (15%), Serratia (10%), and Enterobacter (7%). Comparing the microbial communities in urban and rural sites revealed no substantial variation in their composition across the breeding sites; however, across the developmental stages, the bacterial communities of mosquitoes varied greatly. Among the mosquito larvae, Anophelines larvae were present in 62.4% of the habitats, Culicine larvae in 8%, Aedes larvae in 25.8% while there was a co-occurrence of Culicine and Aedes larvae in 3.2% of the habitats. Two members of the Anopheles gambiae (Anopheles arabiensis and Anopheles colluzzii) family were identified as malaria vectors using polymerase chain reaction. High knockdown rates and resistance were observed in rural and urban Local Government Areas (LGAs) in Ogun state.