How did the new virus develop? Where did it come from?
In general, influenza viruses commonly stick to one species when it comes to infection; for example, dogs and cats don’t get seasonal flu from their owners. However, under the right conditions, influenza viruses from different species are capable of mixing and swapping genes (this is called reassortment), resulting in a new virus. Swine flu can merge with other influenza viruses, such as avian or human flu, to produce new strains. The 2009 H1N1 flu virus consists of North American swine influenza viruses, North American avian influenza viruses, human influenza viruses and swine influenza viruses found in both Asia and Europe.
