Malaria vectors composition and vectorial transmission indices in selected rural and urban areas of Imo state, Nigeria

A combined field and laboratory investigation was conducted in selected communities from Obowo and Owerri North Local Government Areas of Imo State to determine the status of malaria in relation to mosquito vector for rainy and dry seasons. The pyrethrum knock down technique (PKD) was employed ones monthly in the morning hours (6:00am-10.00am) for collection of mosquitoes. The mosquitoes caught were taken to the Laboratory for identification, dissection and infectivity assessment using standard methods. Two malaria vectors Anopheles gambiae and Anopheles funestus sl were identified as major vectors of the disease. The proportions of indoor resting An. gambiae (53.6% vs 46.37%) and An. funestus (50.00% vs 50.00%) did not differ significantly for urban and rural areas (p>0.05). similarly, their indoor resting densities (IRD) 1.43% vs 1.45% as well as average bite/person/night (0.95 vs 1.16) had no difference between rainy and dry seasons. The proportions of the vectors and human biting rates (HBR) 1.56% vs 1.25% were comparable. July (55.75%) and May (50.60%) had the highest mosquito for rainy season while December (56.4%) and October (47.3%) for dry season. In these areas, the proportions of the transmitting vectors could not differ (p>0.05). Overall, sporozoite infection rates were 83.33% and 16.33% for species from urban and rural areas respectively. Monthly variations in density and parity were 57.95% and 42.04% for An. gambiae and An. funestus while monthly entomological inoculation rates (EIR), monthly biting rate (MBR) and monthly sporosites rate (SPR) were 0.021, 1,86% and 1.17% accordingly. HBR, SPR and EIR between urban and rural areas were (0.87% vs 0.98%), (0.41% vs 1.85%), (0.003 vs 0.018) respectively. From the results of this study it appeared that An. gambiae and An. funestus had vectorial capacity in malaria transmission despite low infectivity rate of salivary glands. The comparable rates of infection between urban and rural areas is a serious concern and could indicate the dynamics of vectors and infection status. This put to rest discrepancies about the relationship between malaria transmission and vector composition and signals the scalling up of integrated strategy that includes good environmental sanitation.