Impact of climate and mosquito vector abundance on sylvatic arbovirus circulation dynamics in Senegal

Abstract

Sylvatic arboviruses have been isolated in Senegal over the last 50 years. The ecological drivers of the pattern and frequency of virus infection in these species are largely unknown. We used time series analysis and Bayesian hierarchical count modeling on a long-term arbovirus dataset to test associations between mosquito abundance, weather variables, and the frequency of isolation of dengue, yellow fever, chikungunya, and Zika viruses. We found little correlation between mosquito abundance and viral isolations. Rainfall was a negative predictor of dengue virus (DENV) isolation but a positive predictor of Zika virus isolation. Temperature was a positive predictor of yellow fever virus (YFV) isolations but a negative predictor of DENV isolations. We found slight interference between viruses, with DENV negatively associated with concurrent YFV isolation and YFV negatively associated with concurrent isolation of chikungunya virus. These findings begin to characterize some of the ecological associations of sylvatic arboviruses with each other and climate and mosquito abundance.

Figure 1.

Summary of DENV, YFV, CHIKV, and ZIKAV isolates from 1962 to 2008. Left shows the number of DENV, YFV, CHIKV, and ZIKAV isolates over time by species. Scales on the right indicate the number of isolations. Right shows the Fourier power spectra with Daniell smoothers of (3,3) with 95% bootstrap CIs for the aggregated DENV, YFV, CHIKV, and ZIKAV isolates. Species were included if there was an isolation over the study period. Patas indicates opportunistic isolations from Erythrocebus patas, papio indicates Papio papio, aethiops indicates Chlorocebus aethiops, and human indicates humans.

Figure 2.

Maps show the location of Kedougou, Senegal in relation to Dakar, Senegal (panel A), and the region of Kedougou (panel B).

Figure 3.

Aedes mosquito captures and cross-correlation. Figure shows time series of Ae. luteocephalus and Ae. furcifer/Ae. taylori captures over time (A) with the corresponding cross-correlation plot (B) and Fourier spectra (C and D). Hatched area in B indicates 95% CI assuming an underlying white noise process. We see marked cross-correlation between mosquito isolates up to lags of 7 years. Ae. furcifer/Ae. taylori have a dominant periodicity of 8 years, and Ae. luteocephalus has a dominant periodicity of 20 years.

Figure 4.

Relationships between mosquito species through virus isolations. Virus isolations were summed across each mosquito species. A dendrogram was calculated using Euclidian distance between viral isolations in each mosquito species. Distance matrix below the dendrogram reports the Spearman correlation between the viral times series.

Figure 5.

Cross-correlation of DENV isolates and other virus isolates. The figure shows a time series of DENV isolates compared with the other virus isolates over time (A, C, and E) with corresponding cross-correlation plots (B, D, and F). Hatched areas in B, D, and F indicate 95% CI for correlation assuming an underlying white noise process. We observed significant cross-correlation between DENV and YFV at −12-year lag, significant cross-correlation between DENV and CHIKV at −11-year lag, and significant cross-correlation between DENV and ZIKAV at a 1-year lag.

Figure 6.

Cross-correlation of YFV isolates and other virus isolates. The figure shows a time series of YFV isolates compared with the other virus isolates over time (A, C, and E) with corresponding cross-correlation plots (B, D, and F). Hatched areas in B, D, and F indicate 95% CI for correlation assuming an underlying white noise process. We see significant cross-correlation between YFV and CHIKV at 1- and 8-year lags and 2- and 5-year lags for ZIKAV. This figure appears in color at www.ajtmh.org.

Figure 7.

Cross-correlation of CHIKV isolates and other virus isolates. The figure shows a time series of CHIKV isolates compared with the other virus isolates over time (A, C, and E) with corresponding cross-correlation plots (B, D, and F). Hatched areas in B, D, and F indicate 95% CI for correlation assuming an underlying white noise process. This figure appears in color at www.ajtmh.org.

Figure 8.

Cross-correlation of ZIKAV isolates and other virus isolates. The figure shows a time series of ZIKAV isolates compared with the other virus isolates over time (A, C, and E) with corresponding cross-correlation plots (B, D, and F). Hatched areas in B, D, and F indicate 95% CI for correlation assuming an underlying white noise process. This figure appears in color at www.ajtmh.org.