Characteristics of Anopheles arabiensis larval habitats in selected urban areas in Kafta Humera district of Tigray Region, northwestern Ethiopia

Abstract

Introduction: Mosquito Larval Source Management could be a valuable additional tool for malaria vector control especially in small urban hotspots where the breeding sites are limited in scope and where indoor residual spraying is not applied.
Objective: This study aimed to assess the abundance of potential mosquito breeding sites and identify the most important larval habitats of Anopheles arabiensis in urban settings of the agriculturally important district of Kafta Humera in western Tigray, northwestern Ethiopia.
Methods: Cross sectional larval surveys were conducted in October 2016 and 2017 in Setit-Humera town and nearby semi-urban communities of Adebay and Rawyan, in western Tigray. All water bodies encountered were sampled using standard dippers and their physical features recorded. A total of 132 potential mosquito breeding sites were visited and six aquatic habitats containing Anopheles larvae were identified: rain puddles, riverbed pools, vehicle ruts, leaking water pipes, dugouts, and artificial containers.Anopheline aquatic stages collected were reared and the emerged adults identified by morphological means. Sub-samples of Anopheles gambiae s.l were identified by PCR in a parallel insecticide susceptibility bioassay study. Logistic regression analysis was used to determine the key ecological factors explaining the different densities of mosquito larvae.

Results: Of the 132 habitats visited, 70% were positive for anopheline aquatic stages, of which 82% comprised of high larval density sites. Eighty eight percent of the larval positive habitats also had the pupal stages, indicating the high productivity of the habitats. Ninty nince percent of the 4,925 morphologically identified Anopheles species were Anopheles gambiae s.l, a subsample of which was identified as Anopheles arabiensis by PCR. Anopheles arabiensis larvae were more likely to be found in small and fully sunlit water bodies located within 10-20 meters of human habitations. Vehicle ruts were 12 times (OR = 12; P < 0.001) more likely to be colonized by anopheline larvae than puddles and 5 times (OR = ??? P=0.01) more likely than riverbed pools. Overall, human made water bodies were 5 times (OR = 5.19; P = 0.001) more likely to be colonized by anopheline larvae than natural water bodies. Besides, water bodies encountered in Raywan were nearly 6 times (OR = 5.64.; p < 0.001) and those in Adebay 5 times (OR=5.23; P = 0.003) more likely to host Anopheles arabiensis stages than water bodies in Humera town.

Conclusion: The findings suggest that targeting smaller human-made aquatic habitats could result in effective larval control of Anopheles arabiensis in the study area. Frequent surveillance of mosquito breeding sites, especially during the rainy season, is considered necessary for effective control planning.