Fig. 1: Phylogeographic reconstruction of West Nile virus lineage 1 (WNV L1) strains.

a Geographic diffusion pattern of 80 WNV L1 genomes and their ancestors was reconstructed. African and European countries from which the samples come from are coloured in dark orange and blue, respectively. Black areas correspond to the 80% HPDs of the inferred location. The time of each area or sample is indicated by different shades (black for areas and red for dots), with the oldest samples corresponding to the most intense shade. The main events of the diffusion of the virus are indicated on the map, with numbers from 1 to 6: 1) introductions to West and East of Africa, 2) first introduction in Morocco and then Spain, 3) movement towards France and Italy, 4) back reintroductions from Spain to Morocco and from Italy to Senegal, 5) introduction from Senegal to France in 2015, and 6) back introduction from Italy to Senegal. The direction of the spread of the virus is indicated by arrows, while colours indicate movements happened only in Africa or involving Africa and Europe (in green) and routes that took place entirely in Europe (in yellow). Dotted arcs indicate back reintroductions from Europe to Africa. b A molecular clock shows the phylogenetic relationships between the same 80 WNV L1 genomes. Light orange dots indicate nodes with a posterior probability <0.9, while 95% HPDs of the median ages are indicated by blue bars. African and European sequences are coloured by continent. The time of the most recent common ancestor (tMRCA) for Clade 1A was estimated to be around 1919. On the right, inside Clade 1A, three groups of interest are highlighted: cluster 2, Western Mediterranean clade 1 (WMed-1), and Western Mediterranean clade 2 (WMed-2). The map in Fig. 1 has been produced using free vector and raster map data from Natural Earth (naturalearthdata.com), downloaded from a web platform freely available at https://geojson-maps.ash.ms/.