Click and drag or use the buttons below to move the model.
The viral envelope (gray) and viral proteins (red) involved in binding to host cells are shown. The spherical core is not visible.
Influenza A virus occurs worldwide. There are many types of influenza viruses that vary in the severity of symptoms they cause and in their host range. Influenza viruses have a segmented genome, which means that there are multiple separate sections of the genome, not joined to each other. Segmentation provides an additional mechanism for the evolution of new types of viruses. When two or more influenza viruses infect a single cell, genome segments can reassort to produce a new combination of segments and give rise to a new virus strain. Every year, new strains can infect humans, causing seasonal influenza. Sometimes more dangerous strains emerge, such as the 2009 H1N1 pandemic strain of influenza, also called swine flu, which was the result of reassortment between human, avian, and swine influenza strains.