The Effects of Mean Temperature and Diurnal Temperature Range on West Nile Virus Transmission

Temperature is a major driver of arbovirus transmission, and a changing climate is expected to affect this process significantly. Most experimental studies rely on constant temperatures and overlook realistic daily temperature fluctuations that impact vector-pathogen interactions. The nonlinear relationship between temperature and vector traits responsible for pathogen transmission suggests that daily fluctuating temperatures produce phenotypes important for transmission distinct from those at constant temperatures. Here, we tested whether realistic variations in mean temperature and diurnal temperature range (DTR) influence West Nile virus (WNV) transmission. We experimentally infected colonized Culex tarsalis with WNV-infectious blood meals and maintained them under constant and fluctuating temperature regimes. We quantified how temperature, DTR, and incubation time shaped several outcomes (infection, dissemination, infectiousness, WNV loads in mosquito saliva and mosquito survival). We also integrated survival and infectiousness probabilities to infer implications for transmission. We observed strong effects of temperature on the WNV infection dynamics, viral loads and mosquito survival. Although the probability of initial infection was similar among all temperature regimes, dissemination and infectiousness were constrained by temperature. Dissemination and infectiousness were highest at 26{degrees}C and reduced at cooler (22{degrees}C) and warmer (30{degrees}C) temperatures. Fluctuating temperatures significantly decreased infection and dissemination probabilities, while the probability of becoming infectious was driven primarily by mean temperature rather than DTR. Mosquito survival probability was temperature dependent, and fluctuating regimes increased mortality risk by 1.95-fold. Integrating mosquito survival and infectiousness dynamics demonstrated that, although at higher temperatures the extrinsic incubation period is shorter, reduced mosquito lifespan can limit viral transmission. Together, these results indicate that overall WNV transmission is affected by temperature-dependent viral dynamics and host physiological constraints. Fluctuating temperature regimes significantly delay viral dissemination within the host, especially at the optimal temperature (26{degrees}C). Measurement of infection outcomes under constant temperatures treatments may lead to over/under estimation of transmission parameters in epidemiological models, therefore integrating fluctuating temperature treatments into mechanistic models of transmission can improve estimates of when and where WNV transmission is most likely to occur.