Temporal connections between Culex tarsalis abundance and transmission of western equine encephalomyelitis virus in California - PubMed (original) (raw)
Temporal connections between Culex tarsalis abundance and transmission of western equine encephalomyelitis virus in California
Christopher M Barker et al. Am J Trop Med Hyg. 2010 Jun.
Abstract
Definition of targets for vector control requires an understanding of the relationship between vector abundance and the intensity of arbovirus transmission. Using an extensive surveillance dataset with observations from sentinel chicken flocks and mosquito traps paired in time and space, hierarchical autoregressive logistic regression models were developed to predict the probability of seroconversion in chickens for western equine encephalomyelitis virus (WEEV) based on the relative abundance of the principal vector, Culex tarsalis. After adjustments for confounders, the abundance of Cx. tarsalis 29-42 d before the date of chicken sampling was credibly associated with the risk of WEEV transmission in both the Central and Coachella Valleys, and a doubling of relative Cx. tarsalis abundance was associated with a 58% increase in the odds of seroconversion. The critical time windows identified in our study highlight the need for surveillance of vector populations and forecasting models to guide proactive vector control measures before the detection of transmission to sentinel chickens.
Figures
Figure 1.
Map of California showing the chicken flock sites included in this study and boundaries for counties. The locations of the Central and Coachella Valleys are indicated. The lower graph shows mean monthly temperature anomalies as an indication of year-to-year variation during the 1992–2000 study periods.
Figure 2.
Percentages of chickens that seroconverted for western equine encephalomyelitis virus (WEEV) over the entire 1992–2000 study period for each half-month, Jun–Oct, in the Central and Coachella Valleys.
Figure 3.
Changes in deviance information criterion (DIC) values on addition of the lagged Culex tarsalis predictor (upper panel) shown with odds ratios (ORs) with 95% confidence intervals (CIs) for western equine encephalomyelitis virus (WEEV) seroconversion for a 2-fold increase in relative Cx. tarsalis abundance (lower panel). Each DIC-OR pair represents a model fitted for the specified 2-week (14-d) interval before the bleed date for sentinel chickens.
Figure 4.
Predicted probabilities of biweekly seroconversion (height of surfaces) based on daily minimum temperatures (8–21 d lag), daily maximum temperatures (36–49 d lag), and Culex tarsalis ♀/2 weeks (29–42 d lag). Because associations of seroconversion probabilities with maximum temperatures differed between the valleys, associations are shown for the Central Valley (A and C), Coachella Valley (B and D), and both valleys (E). Grid lines represent the 50th–95th percentiles for each predictor. _Z_-axis scales are consistent within rows for comparisons between valleys. This figure appears in color at
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Figure 5.
Schematic showing the Culex tarsalis abundance and temperature predictors from the final model, positioned at their respective critical time lags. Survival of Cx. tarsalis (80%/day) is depicted by the decay curve through the end of the transmission window for detection on the sampling date. This figure appears in color at
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References
- California Department of Public Health . California mosquito-borne virus surveillance and response plan. Mosquito and Vector Control Association of California, University of California; 2008. http://westnile.ca.gov/downloads.php?download_id=820&filename=2008_CA_Mo... Available at. Accessed August 19, 2008.
- Moore CG, McLean RG, Mitchell CJ, Nasci RS, Tsai TF, Calisher CH, Marfin AA, Moore PS, Gubler DJ. Guidelines for Arbovirus Surveillance Programs in the United States. Ft. Collins, CO: DVBID, CDC, PHS, U.S. Dept. Health Human Services; 2002. pp. 1–81.
- Dye C. Vectorial capacity: must we measure all its components? Parasitol Today. 1986;2:203–209. -PubMed
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