2.1 Study Area and Study Population
The study was done in ten villages of Zoba Maekel and five administrative areas of Asmara. All study sites are located in an area elevating from 2109 – 2349 m ASL. In the last 8 years, Asmara received average precipitation of 103.9 mm in Summer (June up to August) season, with intermittent rain in Spring (March up to May) and Autumn (September up to November) averaging 32.6 and 15.9 mm correspondingly. At the same period, average minimum and maximum mean temperature in Summer was 12.2 and 24.2 0C, with average humidity of 71.4%. According to their respective local administrations, most of the localities get water from wells, drills or ponds; while, residents of the five administrative areas of Asmara- Sembel, Acria, Abashawl, Godaif and Maychehot- have piped water system. The people of the ten villages mainly depend on farming and animal rearing for their daily livelihood, while most inhabitants of Sembel, Akria, Maychehot, Abashawl, and Godaif are government or private employees, and traders.
2.2 Study Design and Sampling
Descriptive cross sectional study was conducted in fifteen locations during September 2019. Systematic random sampling was used in selecting the 50 households from each study area with the exception of Dembezawl, having only 40 households, resulting to a total of 740 households. Since this study was done instantaneously after the rainy season, all households were considered to have water holding containers and included in the sampling frame. During sample selection, all selected households were coded so as to avoid repetition. All households situated in all the study sites were eligible to be included in the study. Closed households or residences of non-consenting owners were not considered during household sampling.
2.3 Tools and materials
Dipper, 30 ml pipettes, vials, enamel tray, record forms, pen, pencil, eraser, note book, GPS for measurement of elevation, flash light, marker and adhesive tape for labelling were used in the field. In the laboratory, cages, tetramin, enamel tray, pipettes, 250 ml plastic cups with mesh, aspirator, freezer, silicajel, dissecting microscope and zoo Taxa key for identification were used.
2.4 Ethical approval and data collection process
The paper received approval from Ministry of Health (MoH), Zoba Maekel, Research Ethical Review Committee. At the study sites, consent was obtained from the residents of selected households, then, a very careful investigation was done in every household. The data collection team tried to identify water holding containers which may harbour the immature stages of the mosquito indoor as well as outdoor. Using various materials and techniques, samples were collected from different containers and recorded in an entomological form [19]. Data collection was finalized within ten days.
Standard dipping (300ml) was done to collect the immature- larvae and pupae- from water containers having wide openings with >1 litters of water. Whereas pipetting (5ml plastic pipette) was applied for smaller functional containers after permission has been granted from the owners. Collection from discarded objects like tins and small bottles was done by emptying to trays and collecting by pipettes.
All the larvae and pupae collected were put in loosely closed vials labelled with date, household number, location and container type. They were carefully transferred to the medical entomology laboratory at Asmara College of Health Sciences within the same day of collection. In the laboratory, they were classified according to their stages, location, container and date of collection. They were separated in to either Aedes or Culex genus. Tertramin was given to the larvae till they transformed to pupae, while the pupae were put in a netted cage. Morphological identification was done for all the emerged adults in a dissecting microscope using the Zoo Taxa key.
2.5 Data analysis
After data collection, data were entered into SPSS (version 20) and descriptive analysis was done in order to determine the breeding preference of the immature mosquito and productivity of different containers. The risk indices, House Index (HI), Container Index (CI) and Breteau Index (BI) for each site were calculated using Microsoft excel spreadsheet by the following formulas: