| Summary: | Background & objectives: Generally, indepth understanding of the epidemiology of malaria is considered a prerequisite for planning effective control measures in the endemic regions like sub-Saharan Africa. This study focuses on the relationship of entomological inoculation rates (EIRs) to malaria incidence and prevalence rates across eco-vegetational zones in Bayelsa State, Nigeria.
Methods: Mosquito sampling was undertaken in seven towns/villages in seven local government areas (LGAs) in three eco-vegetational zones. Adults were collected twice quarterly by the pyrethrum spray catch (PSC) technique. Anophelines were separated morphologically and the sibling species were identified using PCR. Detection of circumsporozoite (CS) antigen by ELISA was used for determining mosquito infection rates. Man-biting, sporozoite and entomological inoculation rates were calculated by standard methods. Simultaneously, malaria incidence and prevalence rates were calculated using data obtained from hospitals and by examination of blood smears from consenting adults.
Results: The estimated mean man-biting rate (MBR) over a 2-yr period was 6.88 bites/person/night. The highest MBR of 16.9 was in the mangrove coastal water forest and the least, 11.3, was in brackish water swamp forest; differences were significant (t = 12.083; p<0.05). The mean sporozoite rate of Anopheles gambiae sensu lato (s.l.) was 11%. The highest mean sporozoite rate was 13.4% for An. gambiae sensu stricto (s.s.), followed by 7.9% for An. arabiensis and the least was 0.4% for An. melas. Seasonal rates varied, highest for An. gambiae s.s. in the dry season, but highest for An. arabiensis in the wet season. The annual entomological inoculation rate of An. gambiae s.l. over a 2-yr period was 80.50 infective bites/person/year; the highest, 70.35 was in An. gambiae s.s. and the least, 0.15 in An. melas. When prevalence (PR), incidence (IR) and entomological inoculation (EIR) rates were incorporated in a logistic regression model, they showed 70.5 and 64% accuracy in predicting the relationship between EIR and, incidence and prevalence rates respectively.
Interpretation & conclusion: Based on EIR values malaria transmission was classified as stable when EIR was >1.5 or unstable when EIR was ≤ 1.5. Although, earlier studies have shown correlation between EIRs and malaria PR, this study demonstrated a significant correlation between EIRs and malaria incidence rates.
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