Malaria transmission intensity and dynamics of clinical malaria incidence in a mountainous forest region of Ghana.

Abstract

Background: Malaria transmission is heterogeneous. Villages close to each other may have very different transmission characteristics. The presence and abundance of malaria vectors is governed by local ecology and microclimate. Knowledge of the dynamics of transmission is important for planning and evaluation of malaria control strategies. This study investigated the heterogeneity of malaria transmission in preparation for a vaccine trial and offers insights into dynamics of malaria incidence in the forest zone of Ghana.

Methods: Malaria transmission was assessed in four villages with different micro-ecological features in the forest zone of the Akwapim-Mampong Range in Ghana, water shed with rivers flowing north to Lake Volta in the south. Human landing catches (HLC) of mosquitoes were conducted and Plasmodium falciparum circumsporozoite rates were assessed by ELISA. Sporozoite prevalence, annual biting rates (ABR) and entomological inoculation rates (EIR) from the four study sites were compared with climatological and ecological data. Regression analysis was used to compare transmission data and blood parasite prevalence, parasite density (PD) and malaria episodes from children in the study area. Additionally we examined trends in confirmed clinical malaria incidence from 2005 -2012.

Results: In total 1307 Anopheles gambiae s.l. and 54 An. funestus females were caught by HLC from November 2003 to August 2005. Sporozoites in Anopheles vectors in four villages ranged from 4.0 to 10.2%, ABR from 371 to 1890 and EIR from 40 to 158. Linear regression on parasitological and clinical data of children from the villages revealed that the ABR significantly influenced the parasite density (PD) of P. falciparum.

Conclusion: Malaria transmission was intense and heterogeneous and corresponded to the micro-ecological differences. Malaria transmission in the early evening hours before people went to sleep was enough to sustain stable malaria. Scaling up preventive measures to reduce exposure to vectors will be effective in reducing parasitemia in children. Variations in transmission intensity must be considered when evaluating impact of control strategies and interventions such as the vaccine trials.