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Shifting patterns of Aedes aegypti fine scale spatial clustering in Iquitos, Peru.

LaCon G, Morrison AC, Astete H, Stoddard ST, Paz-Soldan VA, Elder JP, Halsey ES, Scott TW, Kitron U, Vazquez-Prokopec GM - PLoS Negl Trop Dis (2014)

Bottom Line: The extent of clustering was used to quantify the probability of finding spatially correlated populations.Our findings have implications for understanding Ae. aegypti distribution and for the design of surveillance and control activities relying on household-level data.Focusing efforts in large geographic areas with historically high levels of transmission may be more effective than targeting Ae. aegypti hotspots.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Emory University, Atlanta, Georgia, United States of America.

ABSTRACT

Background: Empiric evidence shows that Aedes aegypti abundance is spatially heterogeneous and that some areas and larval habitats produce more mosquitoes than others. There is a knowledge gap, however, with regards to the temporal persistence of such Ae. aegypti abundance hotspots. In this study, we used a longitudinal entomologic dataset from the city of Iquitos, Peru, to (1) quantify the spatial clustering patterns of adult Ae. aegypti and pupae counts per house, (2) determine overlap between clusters, (3) quantify the temporal stability of clusters over nine entomologic surveys spaced four months apart, and (4) quantify the extent of clustering at the household and neighborhood levels.

Methodologies/principal findings: Data from 13,662 household entomological visits performed in two Iquitos neighborhoods differing in Ae. aegypti abundance and dengue virus transmission was analyzed using global and local spatial statistics. The location and extent of Ae. aegypti pupae and adult hotspots (i.e., small groups of houses with significantly [p<0.05] high mosquito abundance) were calculated for each of the 9 entomologic surveys. The extent of clustering was used to quantify the probability of finding spatially correlated populations. Our analyses indicate that Ae. aegypti distribution was highly focal (most clusters do not extend beyond 30 meters) and that hotspots of high vector abundance were common on every survey date, but they were temporally unstable over the period of study.

Conclusions/significance: Our findings have implications for understanding Ae. aegypti distribution and for the design of surveillance and control activities relying on household-level data. In settings like Iquitos, where there is a relatively low percentage of Ae. aegypti in permanent water-holding containers, identifying and targeting key premises will be significantly challenged by shifting hotspots of Ae. aegypti infestation. Focusing efforts in large geographic areas with historically high levels of transmission may be more effective than targeting Ae. aegypti hotspots.

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Related in: MedlinePlus

Spatial correlation between pupae and adult presence.Results from the bivariate k-function quantifying the scales of spatial association between pupae and adult male and female Ae. aegypti presence during 9 entomologic surveys spanning between 2009 and 2011. Number inside each plot indicates the survey number. Solid lines represent observed values whereas dashed lines the random expectation for an alpha value of 0.05. Analyses were performed to the combined dataset of the Maynas and Tupac Amaru neighborhoods.
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pntd-0003038-g003: Spatial correlation between pupae and adult presence.Results from the bivariate k-function quantifying the scales of spatial association between pupae and adult male and female Ae. aegypti presence during 9 entomologic surveys spanning between 2009 and 2011. Number inside each plot indicates the survey number. Solid lines represent observed values whereas dashed lines the random expectation for an alpha value of 0.05. Analyses were performed to the combined dataset of the Maynas and Tupac Amaru neighborhoods.

Mentions: Figure 3 shows the results of the bivariate k-functions applied to test the scale up to which pupae and adult infestation were associated during nine entomologic surveys between 2009 and 2011. Given the lack of difference in global clustering between neighborhoods, results were pooled to show the overall scale up to which pupae and adults are associated. When the observed value (solid line) is higher than the random expectation (dashed line) spatial association between variables occurs at such a distance (Figure 3). For 4 out of 9 surveys (44%), pupae and adults were clustered within the household (at a distance of 5 m or less) (Figure 3). A very focal level of association between pupae and adults was found when clustering occurred beyond the household (Figure 3); the average ±SD clustering distance was 11.4±5.4 m. Collections performed in December-January (surveys 3, 6 and 9) had higher extent of association between pupae and adults (15–17 meters) compared to the remaining surveys (up to 5 m), indicating that during those months either the extent of populations is larger or the abundance of Ae. aegypti is more patchily distributed.


Shifting patterns of Aedes aegypti fine scale spatial clustering in Iquitos, Peru.

LaCon G, Morrison AC, Astete H, Stoddard ST, Paz-Soldan VA, Elder JP, Halsey ES, Scott TW, Kitron U, Vazquez-Prokopec GM - PLoS Negl Trop Dis (2014)

Spatial correlation between pupae and adult presence.Results from the bivariate k-function quantifying the scales of spatial association between pupae and adult male and female Ae. aegypti presence during 9 entomologic surveys spanning between 2009 and 2011. Number inside each plot indicates the survey number. Solid lines represent observed values whereas dashed lines the random expectation for an alpha value of 0.05. Analyses were performed to the combined dataset of the Maynas and Tupac Amaru neighborhoods.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4125221&req=5

pntd-0003038-g003: Spatial correlation between pupae and adult presence.Results from the bivariate k-function quantifying the scales of spatial association between pupae and adult male and female Ae. aegypti presence during 9 entomologic surveys spanning between 2009 and 2011. Number inside each plot indicates the survey number. Solid lines represent observed values whereas dashed lines the random expectation for an alpha value of 0.05. Analyses were performed to the combined dataset of the Maynas and Tupac Amaru neighborhoods.
Mentions: Figure 3 shows the results of the bivariate k-functions applied to test the scale up to which pupae and adult infestation were associated during nine entomologic surveys between 2009 and 2011. Given the lack of difference in global clustering between neighborhoods, results were pooled to show the overall scale up to which pupae and adults are associated. When the observed value (solid line) is higher than the random expectation (dashed line) spatial association between variables occurs at such a distance (Figure 3). For 4 out of 9 surveys (44%), pupae and adults were clustered within the household (at a distance of 5 m or less) (Figure 3). A very focal level of association between pupae and adults was found when clustering occurred beyond the household (Figure 3); the average ±SD clustering distance was 11.4±5.4 m. Collections performed in December-January (surveys 3, 6 and 9) had higher extent of association between pupae and adults (15–17 meters) compared to the remaining surveys (up to 5 m), indicating that during those months either the extent of populations is larger or the abundance of Ae. aegypti is more patchily distributed.

Bottom Line: The extent of clustering was used to quantify the probability of finding spatially correlated populations.Our findings have implications for understanding Ae. aegypti distribution and for the design of surveillance and control activities relying on household-level data.Focusing efforts in large geographic areas with historically high levels of transmission may be more effective than targeting Ae. aegypti hotspots.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Emory University, Atlanta, Georgia, United States of America.

ABSTRACT

Background: Empiric evidence shows that Aedes aegypti abundance is spatially heterogeneous and that some areas and larval habitats produce more mosquitoes than others. There is a knowledge gap, however, with regards to the temporal persistence of such Ae. aegypti abundance hotspots. In this study, we used a longitudinal entomologic dataset from the city of Iquitos, Peru, to (1) quantify the spatial clustering patterns of adult Ae. aegypti and pupae counts per house, (2) determine overlap between clusters, (3) quantify the temporal stability of clusters over nine entomologic surveys spaced four months apart, and (4) quantify the extent of clustering at the household and neighborhood levels.

Methodologies/principal findings: Data from 13,662 household entomological visits performed in two Iquitos neighborhoods differing in Ae. aegypti abundance and dengue virus transmission was analyzed using global and local spatial statistics. The location and extent of Ae. aegypti pupae and adult hotspots (i.e., small groups of houses with significantly [p<0.05] high mosquito abundance) were calculated for each of the 9 entomologic surveys. The extent of clustering was used to quantify the probability of finding spatially correlated populations. Our analyses indicate that Ae. aegypti distribution was highly focal (most clusters do not extend beyond 30 meters) and that hotspots of high vector abundance were common on every survey date, but they were temporally unstable over the period of study.

Conclusions/significance: Our findings have implications for understanding Ae. aegypti distribution and for the design of surveillance and control activities relying on household-level data. In settings like Iquitos, where there is a relatively low percentage of Ae. aegypti in permanent water-holding containers, identifying and targeting key premises will be significantly challenged by shifting hotspots of Ae. aegypti infestation. Focusing efforts in large geographic areas with historically high levels of transmission may be more effective than targeting Ae. aegypti hotspots.

Show MeSH
Related in: MedlinePlus