West Nile is a virus which means that West Nile is not a living organism and the only goal the virus has is to reproduce. The virus does this by taking over a host cell, attaching itself to the host cell and takes the cellular machinery needed to replicate itself. Once the virus is done and leaves, the host cell can also be used to infect other cells; therefore spreading the virus throughout the organism. (Campbell, Marfin, Lanciotti & Gubler, 2002).
Smith, Sarene and Still, Preston, "West Nile Virus" (2015). Infectious Diseases Project 2015. 13.