Study area
The study area consists of parts of Imo State, Nigeria located between latitude 5° 101 and 5° 511 North, longitudes 6° 351 and 70281 East known as the Imo River Basin. It is bordered on the North by Anambara State, on the South and West by Rivers State and on the East by Abia State. The area has a population density of 458 persons/km2 and the majority of the population is broadly dispersed in a vast number of rural settlements. There are two main climate regimes: a dry season and a wet season. The mean annual rainfall is between 1,800 and 2,500 millimeters per year. The maximum and minimum temperatures are 31.9°C and 22.5°C respectively while the daily sunshine rate is about 4.4 h. Average relative humidity is about 74% occurring mostly during the wet season, while the rate of evaporation and evapotranspiration are 3.0 mm/day and 136 mm/month respectively. The vegetation is typically rain forest.
Criteria for selection
The Area selected for this study includes Ezinihitte, Aboh Mbaise and Ahiazu Mbaise LGAs. The area apart from being a tropical rain forest which supports breeding of mosquito vectors has no efficient water supply system; hence the inhabitants rely on itinerant water vendors and roof catch during raining months for water supply. Water from the different sources is stored in drums, clay pots and all sorts of metal and plastic containers. The use of container storage of roof water increase breeding points for mosquitoes in the raining months while in the dry season, the seasonal streams, drying up pools, puddles and dug tanks become breeding pools for mosquitoes and their ecological associates. These areas experience stable malaria transmission all year round [8]. More importantly, they were being considered to be selected for the national insecticide treated net distribution program which therefore necessitates that this study should be carried out.
Study design and sampling method
This study was designed to be analytical in nature. Households for the study were selected through a systematic random sampling technique. The technique involved spinning a bottle at the centre of each village which is the market square. The first household in the direction the bottle pointed was picked and assigned a number; every two households were picked until the village was covered. Informed oral consent was also sought and obtained from households that were selected to participate in the study.
Pre-disease survey logistics
The pre disease survey logistics included visits to Local Government Area (LGA) chairmen, traditional rulers of the selected communities and village heads to explain the purpose of the survey and solicit for co-operation. Part of the pre-disease survey logistics included mobilization of the communities and the selection/training of village based field assistants (VBFA) (Male and Females).
Entomological study
Indoor resting mosquitoes were caught fortnightly in randomly selected households in each community between 1800-1600 h using the Pyrethrum Spray sheet Collection (PSC) after all occupants and easily movable objects were removed and immovables were covered in each consented household. White sheets were carefully laid on the entire floor by two assistants. All doors and windows were shut and holes and openings eg between hinges were covered with newsprints. The rooms were then space sprayed with pyrethrum spray and kept closed for 10 min after which they were opened. Fallen mosquitoes were collected from the sheets and packed into petri dishes with labels of the house numbers, date of collection and transported to the laboratory for determination of transmission intensity or entomological inoculation rates.
In the laboratory, the female mosquitoes were identified and dissected to determine parity by observing the degree of coiling of their ovarian tracheoles [9]. The salivary glands of parous mosquitoes were extracted, stained with giemsa and examined for malaria parasites under the microscope [10]. Malaria transmission intensity expressed as Mean entomological Inoculation rates (EIRm) were then calculated as infectious bite per person per night (ib/p/n) using standard formula [9].
Malaria morbidity study
Structured, pretested questionnaires were administered to one mother/caregiver in each of six hundred and ninety nine (699) selected households by trained field based assistants. In addition key informant interviews were also conducted with 60 community health workers to determine the malaria specific signs and symptoms among children in the study area which includes relapsing fever for 48 hours and headache [5]. Records of total number of outpatient attendance attributed to malaria between 2007-2010 from selected health facilities in the study area were also analyzed. Annual morbidity attributable to malaria was calculated as percentage malaria prevalence of total outpatient cases for the study period.
Ethical approval
Ethical approval for this study was given by the ethical committee of the Federal Medical Center, Owerri Nigeria. The study was also reviewed by the institutional Review Board (IRB) of the Department of Animal and Environmental Biology, Imo State University, Owerri, Imo State.