The West Nile virus is a re-emergent pathogen naturally circulating in western Andalusia since, at least, 2003. Nevertheless, the number of cases of West Nile Disease in humans had been scarce until 2020, when an unprecedented increase of cases in humans was registered. In this talk, I present the objectives of my thesis that aims to assess the effect of biotic and abiotic factors on the occurrence of the 2020 outbreak. To do so, I will study changes associated to WNV vectors and vertebrate hosts populations and their interactions with pathogens which could affect the WNV epidemiology. Firstly, I will analyse how environmental conditions influence mosquito abundance, their genetic population structure and the WNV prevalence in mosquitoes. Secondly, I will identify the role of hosts species identity and intrinsic factors like parasite specialization on the pathogen incidence in vertebrate hosts. Finally, I will explore the role of blood feeding preferences of vectors on WNV circulation in the area. With this, I expect to contribute to the understanding of the changes of the epidemiology of WNV during 2020.