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.
Bird flu, or avian flu, is an infectious type of influenza that spreads among birds. In rare cases, it can affect humans. There are many different strains of bird flu virus, most of which don't infect humans. However, two particular strains have caused serious concern in recent years: 1  H5N1 (since 1997). 2  H7N9 (since 2013).