Effects of Temperature on Emergence and Seasonality of West Nile Virus in California

Abstract

Abstract. Temperature has played a critical role in the spatiotemporal dynamics of West Nile virus transmission throughout California from its introduction in 2003 through establishment by 2009. We compared two novel mechanistic measures of transmission risk, the temperature-dependent ratio of virus extrinsic incubation period to the mosquito gonotrophic period (BT), and the fundamental reproductive ratio (R 0 ) based on a mathematical model, to analyze spatiotemporal patterns of receptivity to viral amplification. Maps of BT and R 0 were created at 20-km scale and compared throughout California to seroconversions in sentinel chicken flocks at half-month intervals. Overall, estimates of BT and R 0 agreed with intensity of transmission measured by the frequency of sentinel chicken seroconversions. Mechanistic measures such as these are important for understanding how temperature affects the spatiotemporal dynamics of West Nile virus transmission and for delineating risk estimates useful to inform vector control agency intervention decisions and communicate outbreak potential.

Climate change impacts on West Nile virus transmission in a global context

“…However, it was shown that the replication cycle is completed more quickly in mosquitoes at higher temperatures [38,39], while a clear association was found between extreme heat and outbreak intensity in humans [4,18,22,35,[40][41][42][43]. At the same time, it is important to note that, in some cases, extremely high temperatures begin to slow down mosquito activity.…”

“…In fact, WNV became endemic across most temperate regions of North America [12]. The effects of weather fluctuations on WNV transmission in the USA and Canada have been analysed by several researchers who showed that increased temperatures influence North American WNV distribution and play an important role in the maintenance and amplification of human infection [43,81]. Soverow et al [42] assessed 16 298 human WNF cases from 2001 to 2005 across 17 states in the USA.…”

West Nile Virus Activity in a Winter Roost of American Crows (Corvus brachyrhynchos): Is Bird-To-Bird Transmission Important in Persistence and Amplification?

“…Crows are a widespread, synanthropic, and highly competent host for WNV . In their mechanistic model developed to track the invasion of WNV into California, Hartley et al (2012) showed that outbreaks are unlikely to occur in the absence of crows or other highly competent amplification hosts. Moreover, in southern California, foci of WNV infection in Culex and humans generally overlapped with areas of high crow density and mortality, suggesting the importance of corvids in amplification of the virus (Reisen et al 2006a).…”

Climate, environmental and socio-economic change: weighing up the balance in vector-borne disease transmission

“…Developing an understanding of short-term lags in the effect of exposure and manifestation of the selected health outcome is crucial for correctly capturing true associations [133,134]. These lags might be driven by complex life cycle processes and/or social determinants such as a lack of timely utilization of health care facilities.…”