In early 2009, a virus with an unusual genome popped up in people in central Mexico. It had actually pieces derived from 3 different swine influenza lineages, consisting of a Eurasian lineage not previously observed in the Americas.Beginning in the 1990s, millions of United States pigs were trucked into Mexico, some of which carried classical H1N1 and triple-reassortant H3N2 infections that then spread across the nations northern, central, and eastern regions.
