Landscape ecology of sylvatic chikungunya virus and mosquito vectors in southeastern Senegal

Abstract

The risk of human infection with sylvatic chikungunya (CHIKV) virus was assessed in a focus of sylvatic arbovirus circulation in Senegal by investigating distribution and abundance of anthropophilic Aedes mosquitoes, as well as the abundance and distribution of CHIKV in these mosquitoes. A 1650 km(2) area was classified into five land cover classes: forest, barren, savanna, agriculture and village. A total of 39,799 mosquitoes was sampled from all classes using human landing collections between June 2009 and January 2010. Mosquito diversity was extremely high, and overall vector abundance peaked at the start of the rainy season. CHIKV was detected in 42 mosquito pools. Our data suggest that Aedes furcifer, which occurred abundantly in all land cover classes and landed frequently on humans in villages outside of houses, is probably the major bridge vector responsible for the spillover of sylvatic CHIKV to humans.

Figure 1. Location and land cover characteristics of study area.

Symbols indicating sampling sites are centered around each site but are larger than the actual site in order to enhance visibility; thus some symbols overlap each other or the boundary of sampling blocks while actual sites do not overlap.

Figure 2. Meteorological conditions and abundance of potential CHIKV vectors between June 2009 and January 2001.

The top panel shows mean temperature (solid square) bounded by maximum and minimum temperature (top and bottom bars) each month (www.worldclimate.com). The middle panel shows total precipitation (gray bars) (http://www.tutiempo.net/en/Climate/Kedougou/616990.htm), and total abundance of all sampled vector species (black line) per month. The bottom panel shows the monthly abundance of select mosquito species as indicated by the legend.

Figure 3. Chart showing the mosquito sampling strategy.

Figure 4. Standard (solid black line) and cumulative (solid gray line) Moran's I spatial correlograms.

Solid squares/triangles indicate spatial autocorrelation statistics that remain significant after progressive Bonferroni correction; white squares/triangles indicate statistics that were significant before the correction and non-significant afterwards. The dashed line indicates the expected value of Moran's I under the null hypothesis of no spatial autocorrelation (here: 0.02041). Spatial autocorrelation coefficients for distance classes 10 and 11 are not shown here, because they only include the pairs of study area border point locations and less than 2% of all pairs considered.

Figure 5. LISA maps of vector abundance.

The analyses were based on 9,999 permutations and a pseud significance value of 0.05.

Figure 6. Absolute abundance of potential CHIKV vectors at each site between June 2009–January 2010.

The size of each symbol indicates abundance at each site as indicated in the legend; color indicates the land cover class in which the mosquitoes were collected as indicated in the legend.