Various biological models are used to isolate West Nile virus, but their role as a selection factor that facilitates selection of isolates with certain properties is usually not evaluated. We compared pathogenic properties of three strains of the West Nile virus obtained from one sample of virus-containing material using different models: WNV Volgograd 900m/18 (on the model of suckling mice), WNV Volgograd 900a/18 (on C6/36 cells) and WNV Volgograd 900v/18 (on Vero cells). WNV Volgograd 900m/18 strain demonstrated virulent (LD