This document defines key terms related to zoonotic influenza such as zoonosis, influenza, pandemic, and epidemic. It then provides information about influenza A viruses. Specifically, it notes that influenza A is made up of 8 gene segments that code for 10 proteins, including hemagglutinin and neuraminidase which determine aspects of the virus and are used to classify strains, such as H1N1. It describes how these proteins control how the virus interacts with host cells during the infection process.