Topography as a modifier of breeding habitats and concurrent vulnerability to malaria risk in the western Kenya highlands

Abstract

BackgroundTopographic parameters such as elevation, slope, aspect, and ruggedness play an important role in malaria transmission in the highland areas. They affect biological systems, such as larval habitats presence and productivity for malaria mosquitoes. This study investigated whether the distribution of local spatial malaria vectors and risk of infection with malaria parasites in the highlands is related to topography.MethodsFour villages each measuring 9 Km2 lying between 1400-1700 m above sea level in the western Kenya highlands were categorized into a pair of broad and narrow valley shaped terrain sites. Larval, indoor resting adult malaria vectors and infection surveys were collected originating from the valley bottom and ending at the hilltop on both sides of the valley during the rainy and dry seasons. Data collected at a distance of ≤500 m from the main river/stream were categorized as valley bottom and those above as uphill. Larval surveys were categorized by habitat location while vectors and infections by house location.ResultsOverall, broad flat bottomed valleys had a significantly higher number of anopheles larvae/dip in their habitats than in narrow valleys during both the dry (1.89 versus 0.89 larvae/dip) and the rainy season (1.66 versus 0.89 larvae/dip). Similarly, vector adult densities/house in broad valley villages were higher than those within narrow valley houses during both the dry (0.64 versus 0.40) and the rainy season (0.96 versus 0.09). Asymptomatic malaria prevalence was significantly higher in participants residing within broad than those in narrow valley villages during the dry (14.55% vs. 7.48%) and rainy (17.15% vs. 1.20%) season. Malaria infections were wide spread in broad valley villages during both the dry and rainy season, whereas over 65% of infections were clustered at the valley bottom in narrow valley villages during both seasons.ConclusionDespite being in the highlands, local areas within low gradient topography characterized by broad valley bottoms have stable and significantly high malaria risk unlike those with steep gradient topography, which exhibit seasonal variations. Topographic parameters could therefore be considered in identification of high-risk malaria foci to help enhance surveillance or targeted control activities in regions where they are most needed.

Protein Microarray Analysis of Antibody Responses to Plasmodium falciparum in Western Kenyan Highland Sites with Differing Transmission Levels

“…There, the tremendous variations of malaria transmission intensity in a small spatial scale are caused by substantial differences in altitude, topography and other environmental conditions [6,7,21,22]. We now expand our antibody profiling survey to include 854 P. falciparum polypeptides by using protein microarray technology.…”

Molecular Characterization Reveals Diverse and Unknown Malaria Vectors in the Western Kenyan Highlands

“…The western Kenyan highlands is an area of unstable, sometimes epidemic malaria 34 where anopheline vector dynamics determine the spread and maintenance of malaria transmission. [35][36][37] The aim of our study was to identify Anopheles species present in two neighboring districts in the western Kenyan highlands using both molecular and morphological tools. This study expands upon previously reported findings of unknown and potentially new vector species in Kisii district, 38 detailing the rDNA ITS2 and mtDNA CO1 regions, and includes sequence analysis of two more recent sets of mosquito collections from an area in the neighboring district, Rachuonyo South.…”

Individual- and Household-Level Risk Factors Associated with Malaria in Mutasa District, Zimbabwe: A Serial Cross-Sectional Study

“…Topographical attributes are potentially relevant for habitat suitability of malaria vectors, thus, aspect, slope, and elevation were extracted from the DEM. 13,18 The aspect, which ranges from 0 to 360 degrees, was categorized into three topographically important slope orientations: north-facing, south-facing, and all other slope orientations. In the southern hemisphere, north-facing slopes tend to be warmer and less humid because of more direct sunlight.…”