Viral migration patterns.

The number of viral introductions is represented by the Markov jump counts (posterior expected number of location state transitions, with 95% highest posterior density [HPD] intervals) between the three key US regions: South-central (SC), Southeast (SE), and Midwest (MW). The highest estimates of expected location state transitions are highlighted in bold. Using the estimated number of pigs transported between regions (‘swine-flows’) during years that are well sampled in our study (2005–2008) (Table S2), we estimate the number of pigs transported along each inter-regional route per viral introduction.