Physical and chemical characteristics of Aedes larval habitats in Metema District, Northwest, Ethiopia.

Background: Aedes-transmitted viral diseases such as dengue, chikungunya, yellow fever, and Zika are increasing public health and economic challenge globally. In the absence of treatments and vaccines for arboviral diseases, surveillance and control of Aedes larvae remains a top priority. However, Aedes larvae control strategies relay to a large extent on the knowledge of the distribution and characteristics of their habitats. The study assessed habitats, indices, habitat physico-chemical characteristics and composition of Aedes larvae and pupae in three towns.

Methods: Aedes larvae and pupae were collected in Metema-Yohannes, Kokit, and Gendawuha towns of northwestern Ethiopia, from January 2022 to December 2023 following standard procedures. Aedes larvae/pupae were surveyed along natural and artificial habitats in relation to residential houses, physico-chemical characteristics of habitats characterized, reared to adults and later identified to species based on their morphological features. Data were entered and analyzed using IBM SPSS version 20.0.

Results: Aedes larvae and pupae were abundant in Metema-Yohannes, Kokit and Gendawuha towns. Breteau, house, and container indices exceeded the World Health Organization's risk levels for arboviral diseases. Density of Aedes larvae/pupae was positively correlated with habitat water temperature, conductivity, phosphate, ammonia, total hardness and sulphate both in the artificial and natural habitats (P < 0.001). Adult Ae. aegypti were the most abundant (56.77%; 5106/8993) that emerged from larvae/pupae followed by Ae. vittatus (37.25%; 3350/8993), Ae. communis (2.39%; 215/8993), Ae. opok (0.66%; 60) and Ae. albopictus (0.26; 24). The number of Ae. aegypti emerged from algal habitats was greater than the number from the algae free (p < 0.001) and the number from tadpole free habitats was greater than the number from tadpole infested (p < 0.001). Adults of Ae. vittatus followed a similar trend. The mean number of Ae. aegypti emerged from larvae/pupae of habitats closer to human habitations, not exposed to sunlight, free of emergent vegetation and tyre substrates were significantly (p < 0.001) higher than from habitats of corresponding attributes.

Conclusion: Artificial water-holding containers maintained higher density of Aedes larvae/pupae than natural water-holding containers in Metema-Yohannes, Kokit and Gendawuha towns. Ae. aegypti, Ae. vittatus, Ae. communis, Ae. albopictus and Ae. opok occurred in the towns. Ae. aegypti and Ae. vittatus larvae/pupae were abundant in discarded tyres, Ae. communis in discarded metal containers, and Ae. albopictus and Ae. opok in tree holes during the wet seasons in Metema Woreda, Northwestern Ethiopia. This study indicates the importance of improving Aedes larvae/pupae surveillance and control measures in Metema Woreda, Northwest Ethiopia.