Beyond competence: a mechanistic model of avian demographic drivers in West Nile virus dynamics

BackgroundWest Nile virus (WNV) is a vector-borne zoonotic pathogen maintained in an enzootic cycle between birds and mosquitoes which is considered a significant public health concern in Europe, particularly in relation to its recent increase in reported human cases and range expansion. While a comprehensive understanding of the viruss epidemiological dynamics is essential to inform effective prevention and control strategies, to date significant knowledge gaps remain in quantifying interspecific differences within the complex avian communities involved in WNV circulation. Globally, WNV-infection has indeed been documented across more than 300 bird species, however, whether and how inter-specific differences in avian hosts traits affect the spread of WNV is still largely unknown. A substantial body of research has investigated how epidemiological traits, such as the duration of infection and competence, influence WNV dynamics. However, much less is known about the role of avian demography. Methodology/Principal findingsWe therefore investigated through mathematical modelling the role of avian demographic traits in shaping patterns of mosquito WNV infection dynamics in northern Italy (Lombardy Region, 2016-2018). We focused on the effects of annual offspring production, timing and synchrony of breeding which ultimately affect seasonal abundance of competent avian hosts. We highlighted that timing of breeding has the greatest effect on the number of infected mosquitoes, while annual offspring production influences the timing of the infection peak. Our simulations provide evidence that non-corvid species can have a key impact on WNV transmission. Conclusion/SignificanceThese results can support future research by providing priority bird species to direct further studies and by suggesting that the acknowledgment of spatio-temporal variation in the abundance of competent avian hosts plays a key role in the development of effective surveillance strategies and mosquito control actions. Author summaryWest Nile virus (WNV) is endemic in Italy and represents a significant public health threat in Europe, with increasing cases of severe neuroinvasive disease in humans in recent years. Surveillance data reveal marked spatial and temporal variability in infection dynamics, suggesting that key drivers of WNV transmission remain poorly understood. The contribution of different bird species (over 300 are implicated in the WNV cycle) is often overlooked despite evidence that species-specific traits are critical determinants of WNV infection dynamics. Few studies have examined birds demographic traits, despite their well-established importance in shaping infection dynamics across diseases. Given the challenges in collecting detailed wildlife data, we employed mechanistic models to explore transmission scenarios and test whether avian demographic traits influence bird species roles in WNV transmission and maintenance in Lombardy. Our findings demonstrate that brood size, hatching synchrony, and hatching time significantly affect estimated WNV prevalence in mosquitoes.