Thermal thresholds heighten sensitivity of West Nile virus transmission to changing temperatures in coastal California

Temperature is widely known to influence the spatio-temporal dynamics of vector-borne disease transmission, particularly as temperatures vary across critical thermal thresholds. When temperature conditions exhibit such ‘transcritical variation’, abrupt spatial or temporal discontinuities may result, generating sharp geographical or seasonal boundaries in transmission. Here, we develop a spatio-temporal machine learning algorithm to examine the implications of transcritical variation for West Nile virus (WNV) transmission in the Los Angeles metropolitan area (LA). Analysing a large vector and WNV surveillance dataset spanning 2006–2016, we found that mean temperatures in the previous month strongly predicted the probability of WNV presence in pools of Culex quinquefasciatus mosquitoes, forming distinctive inhibitory (10.0–21.0°C) and favourable (22.7–30.2°C) mean temperature ranges that bound a narrow 1.7°C transitional zone (21–22.7°C). Temperatures during the most intense months of WNV transmission (August/September) were more strongly associated with infection probability in Cx. quinquefasciatus pools in coastal LA, where temperature variation more frequently traversed the narrow transitional temperature range compared to warmer inland locations. This contributed to a pronounced expansion in the geographical distribution of human cases near the coast during warmer-than-average periods. Our findings suggest that transcritical variation may influence the sensitivity of transmission to climate warming, and that especially vulnerable locations may occur where present climatic fluctuations traverse critical temperature thresholds.

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Spatio-temporal Analyses of West Nile Virus Transmission inCulexMosquitoes in Northern Illinois, USA, 2004

Vector-Borne and Zoonotic Diseases ◽

10.1089/vbz.2006.6.91 ◽

2006 ◽

Vol 6 (1) ◽

pp. 91-98 ◽

Cited By ~ 20

Author(s):

Weidong Gu ◽

Richard Lampman ◽

Nina Krasavin ◽

Robert Berry ◽

Robert Novak

Keyword(s):

West Nile Virus ◽

Virus Transmission ◽

West Nile ◽

West Nile Virus Transmission ◽

Spatio Temporal

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Exploring the Spatio-Temporal Dynamics of Reservoir Hosts, Vectors, and Human Hosts of West Nile Virus: A Review of the Recent Literature

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph10115399 ◽

2013 ◽

Vol 10 (11) ◽

pp. 5399-5432 ◽

Cited By ~ 23

Author(s):

Esra Ozdenerol ◽

Gregory Taff ◽

Cem Akkus

Keyword(s):

West Nile Virus ◽

Recent Literature ◽

Temporal Dynamics ◽

West Nile ◽

Spatio Temporal ◽

Reservoir Hosts

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Spatio-temporal impacts of aerial adulticide applications on populations of West Nile virus vector mosquitoes

Parasites & Vectors ◽

10.1186/s13071-021-04616-6 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Karen M. Holcomb ◽

Robert C. Reiner ◽

Christopher M. Barker

Keyword(s):

West Nile Virus ◽

Temporal Trends ◽

Larval Habitat ◽

Post Treatment ◽

Additive Models ◽

Dispersal Ability ◽

Stochastic Variation ◽

West Nile ◽

Spatial Coverage ◽

Spatio Temporal

Abstract Background Aerial applications of insecticides that target adult mosquitoes are widely used to reduce transmission of West Nile virus to humans during periods of epidemic risk. However, estimates of the reduction in abundance following these treatments typically focus on single events, rely on pre-defined, untreated control sites and can vary widely due to stochastic variation in population dynamics and trapping success unrelated to the treatment. Methods To overcome these limitations, we developed generalized additive models fitted to mosquito surveillance data collected from CO2-baited traps in Sacramento and Yolo counties, California from 2006 to 2017. The models accounted for the expected spatial and temporal trends in the abundance of adult female Culex (Cx.) tarsalis and Cx. pipiens in the absence of aerial spraying. Estimates for the magnitude of deviation from baseline abundance following aerial spray events were obtained from the models. Results At 1-week post-treatment with full spatial coverage of the trapping area by pyrethroid or pyrethrin products, Cx. pipiens abundance was reduced by a mean of 52.4% (95% confidence intrval [CI] − 65.6, − 36.5%) while the use of at least one organophosphate pesticide resulted in a mean reduction of 76.2% (95% CI − 82.8, − 67.9%). For Cx. tarsalis, at 1-week post-treatment with full coverage there was a reduction in abundance of 30.7% (95% CI − 54.5, 2.5%). Pesticide class was not a significant factor contributing to the reduction. In comparison, repetition of spraying over three to four consecutive weeks resulted in similar estimates for Cx. pipiens and estimates of somewhat smaller magnitude for Cx. tarsalis. Conclusions Aerial adulticides are effective for achieving a rapid short-term reduction of the abundance of the primary West Nile virus vectors, Cx. tarsalis and Cx. pipiens. A larger magnitude of reduction was estimated in Cx. pipiens, possibly due to the species’ focal distribution. Effects of aerial sprays on Cx. tarsalis populations are likely modulated by the species’ large dispersal ability, population sizes and vast productive larval habitat present in the study area. Our modeling approach provides a new way to estimate effects of public health pesticides on vector populations using routinely collected observational data and accounting for spatio-temporal trends and contextual factors like weather and habitat. This approach does not require pre-selected control sites and expands upon past studies that have focused on the effects of individual aerial treatment events.

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