FIG 9.

Phylogenetic relationships of H1δ-2 viruses collected in U.S. swine, 2005 to 2019. Time-scaled MCC tree inferred for 950 HA (H1δ-2) sequencesfrom IAVs collected in U.S. swine since 2005. The color of each branch indicates the most probable location state: green, commercial swine in North Carolina; blue, commercial swine from other U.S. states, primarily in the Midwest region; purple, exhibition swine from all U.S. states collected for this study. Posterior probabilities are provided for key nodes. The four introductions of H1δ-2 viruses into exhibition swine are indicated by purple boxes. The arrow at the top of the tree indicates the major introduction of H1δ-2 viruses from North Carolina into the Midwest region and thereafter into exhibition swine in 2018. The origins of H1δ-2 viruses via a human-to-swine transmission event in the early 2000s is indicated near the root of the tree.