Now that we know about both prokaryotic and eukaryotic cells, let's look at the endosymbiosis theory. This theory suggests that mitochondria and plastids in eukaryotic cells were once independent prokaryotic cells.
Avian influenza (AI) is an infectious viral disease of birds (especially wild water fowl such as ducks and geese), often causing no apparent signs of illness. AI viruses can sometimes spread to domestic poultry and cause large-scale outbreaks of serious disease.
Type A influenza virus is the most virulent form of influenza and the one that causes the most severe illness. This virus often originates in populations of wild birds, poultry, or swine (including pigs and hogs), so different strains are sometimes referred to as avian (bird) or swine flu.