Temporal and spatial stability of Anopheles gambiae larval habitat distribution in Western Kenya highlands

Abstract

Background: Localized mosquito larval habitat management and the use of larvicides have been proposed as important control tools in integrated malaria vector management programs. In order to optimize the utility of these tools, detailed knowledge of the spatial distribution patterns of mosquito larval habitats is crucial. However, the spatial and temporal changes of habitat distribution patterns under different climatic conditions are rarely quantified and their implications to larval control are unknown.

Results: Using larval habitat data collected in western Kenya highlands during both dry and rainy seasons of 2003-2005, this study analyzed the seasonal and inter-annual changes in the spatial patterns in mosquito larval habitat distributions. We found that the spatial patterns of larval habitats had significant temporal variability both seasonally and inter-annually.

Conclusions: The pattern of larval habitats is extremely important to the epidemiology of malaria because it results in spatial heterogeneity in the adult mosquito population and, subsequently, the spatial distribution of clinical malaria cases. Results from this study suggest that larval habitat management activities need to consider the dynamic nature of malaria vector habitats.

Figure 1

Location of the study area: (upper left) the map of dry season anopheline-positive habitats in 2005 (the black dots are positive habitats and the white dots with black outlines are negative habitats i.e. stagnant aquatic habitats that contain no Anopheles larvae); (lower left) the map of rainy season anopheline-positive habitats in 2005; (right) the map showing the location of the study areas and the regions of Kenya. The scale bar is associated with the two maps on the left sides.

Figure 2

Monthly precipitation: January, February, March, April, and May 2003, 2004, and 2005.

Figure 3

Percentages of stagnant aquatic habitats (A) and anopheline-positive habitats (B) that were observed repeatedly in same locations across seasons and years.