MALARIA RISK MAPPING AND VECTOR SURVEILLANCE IN IFEDORE LOCAL GOVERNMENT AREA OF ONDO STATE.

Abstract

Mosquitoes are dipterous insects of serious public health importance as various species are vectors of diseases. Anophelesspecies are chief nuisance organisms, acting as vector of the various Plasmodium species that cause malaria. The incidence of malaria, is on the rise on a daily basis in Africa due to increase in breeding sites of these vectors created by various human and environmental factors. In the fight against malaria, modern tools and computing gives ample opportunity to explore data, plan ahead of time in vectoral studies to assist in curbing the spread of the disease from source.This study was conducted in Ifedore Local Government Area, one of the 18 Local Government Areas in Ondo State, in the south-western part of Nigeria.Advocacy visits were paid to Community Leaders before sampling were carried out at the sites. Mosquito larvae were collected using standard dippers, handled and transported appropriately to the laboratory. Eleven settlements in the study area were searched for open water bodies andthree collection points were identified in each settlement. These includebreeding sites close to houses, blocked drainages/stagnant water bodies and breeding sites in outpost farm settlements. Geographical coordinates of the sites were recorded,larval density was calculated per site, each site was categorised andphotographed. The physico-chemical factors of the sites were recorded. The collected larvae were reared to adulthood in the laboratory following modified standard procedure, stored in cool and dry environment and identified morphologically using standard keys. Mean, correlation and Chi Square (χ2) analyses were carried out on the physico-chemical parameters and the various species. The morphologically identified Anopheles gambiae s.l. and some Culex pipiens complex were further subjected to molecular analyses using Polymerase Chain Reaction (PCR). The PCR was performed with universal and species specific primers for the organisms, based on the species specific nucleotide sequences in the ribosomal DNA intergenic spacers (IGS), the amplified DNA were separated on a 1.5% agarose gel stained with ethidium bromide and viewed on a UV trans illuminator. All attributes data, on wetlands, vegetation cover, and drainage systems were prepared on 1: 25,000 scale using Arc View 10.3, GIS software and the site number indexed. Remote sensed image, environmental data Land surface temperature (LST), the normalized difference vegetation index (NDVI) and altitude information were derived from satellite images using standard procedures coupled with the measurements from the study. Obtained geographical coordinates from field study were converted into the Cartesian XY Plane and the points plotted on the map that was developed using the ArcView 10.3 software. The morphologically identified mosquitoes were Anopheles gambiae s.l. 348 (194 male and 154 female; 16.97%), Aedes spp 394 (248 male and 146 female; 19.21%), Culex spp 1270 (740 male and 530 female; 61.92%), Mansonia spp 7 (1 male and 6 female; 0.34%) Toxorhynchite spp 20 (14 male and 6 female; 0.98%) and Coquillettidia spp 12 (3 male and 9 female; 0.59%). Sites at Igbara-Oke had the highest larvae abundance (256.67) and the lowest was observed at Ero (90.67). The larvae densities varied with the type of breeding sites. The distance of breeding sites to the nearest residence ranged from 0.5m to 300m. Temperature in all breeding sites ranged from 20.800C to 32.600C; dissolved oxygen, 2.70 to 7.80mg/L; Total Dissolved Solids, 043 to 1933ppm and pH was between 5.30-8.50. Correlation analysis revealed that temperature and dissolved oxygen had significant effect on all the species, as higher values increased their presence. Each of the other physico-chemical parameters had effects on some of the mosquito species.Chi Square (χ2) analysis revealed the species occurred independent of each other. Numerous Anopheles breeding sites (Owode-Owena, Ibuji, Isarun, Ilara, Eero and Aaye), 17 out of 33 sites (51.52%), were found exposed to direct sunlight and were turbid. After PCR identification of all the348 Anophelesgambiae s.l. a total of 340 (97.70%) came out positive while 8 (2.30%) degenerated before molecular analyses. Anopheles arabiensis was 21 (6.05%), Anopheles gambiae s.s. was 315 (90.52%), while Anopheles merus was 4 (1.15%).