This virus was originally referred to as “swine flu” because laboratory testing showed that many of the genes in this new virus were similar to influenza viruses that normally occur in pigs in North America. But further study has shown that the new virus is different from what normally circulates in North American pigs. It has two genes from flu viruses that normally circulate in pigs in Europe and Asia and avian genes and human genes. Scientists call this a “quadruple reassortant” virus.

Source: Centers for Disease Control and Prevention