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West Nile virus (WNV) is a re-emerging zoonotic pathogen with increasing incidence in Europe, producing a recent outbreak in 2020 in Spain with 77 human cases and eight fatalities. However, the factors explaining the observed changes in the incidence of WNV in Europe are not completely understood. Longitudinal monitoring of WNV in wild animals across Europe is a useful approach to understand the eco-epidemiology of WNV in the wild and the risk of spillover into humans. However, such studies are very scarce up to now. Here, we analysed the occurrence of WNV and Usutu virus (USUV) antibodies in 2102 samples collected between 2005 and 2020 from a population of feral horses in Doñana National Park. The prevalence of WNV antibodies varied between years, with a mean seroprevalence of 8.1% (range 0%–25%) and seasonally. Climate conditions including mean minimum annual temperatures and mean rainy days per year were positively correlated with WNV seroprevalence, while the annual rainfall was negatively. We also detected the highest incidence of seroconversions in 2020 coinciding with the human outbreak in southern Spain. Usutu virus-specific antibodies were detected in the horse population since 2011. The WNV outbreak in humans was preceded by a long period of increasing circulation of WNV among horses with a very high exposure in the year of the outbreak. These results highlight the utility of One Health approaches to better understand the transmission dynamics of zoonotics pathogens.

[ES] Una de las consecuencias de la acción humana y el cambio global es el aumento de enfermedades infecciosas no solo en humanos sino también en fauna silvestre. Los efectos negativos de los patógenos pueden ser devastadores llegando a diezmar poblaciones naturales e incluso causar la extinción de especies. Por ello, es imperativo un conocimiento más profundo de los mecanismos y estrategias que estos agentes llevan a cabo durante su ciclo de vida, así como las respuestas inmunológicas y bioquímicas que sus hospedadores naturales muestran durante la interacción hospedador- patógeno. Gracias al desarrollo de metodologías moleculares como la genómica y a través del análisis de transcriptomas hoy en día sabemos un poco más acerca de las cascadas bioquímicas y respuestas inmunológicas que se dan en la interacción hospedador-patógeno. El presente artículo se centra en mostrar los avances en el estudio genómico y transcriptómico de infecciones en aves provocadas por parásitos del género Plasmodium y del Virus del Nilo Occidental. Así mismo, revisamos los problemas a los que los científicos deben hacer frente para un mejor entendimiento de la dinámica hospedador-patógeno, [ENG] Anthropogenic pressure and global change are favouring the increase of infectious diseases not only in humans but also in wildlife. The negative effects of pathogens can be devastating, affecting natural populations and even causing the extinction of species. Therefore, it is fundamental to understand the mechanisms and strategies that these agents develop during their life cycle, as well as the immunological and biochemical responses that natural hosts show during host-pathogen interaction. Development of new molecular tools such as genomics or the analysis of transcriptomes have provided the scientific community significant information about host-pathogen interactions, including the biochemical cascades and immunological responses that occur. This article focuses on showing the advances in this field in birds infected with avian Plasmodium and West Nile Virus. In addition, we also review the problems that scientists must face in order to better understand the host-pathogen dynamics