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.
For the H5N1 subtype of Avian influenza, see Influenza A virus subtype H5N1. Avian influenza â known informally as avian flu or bird flu â refers to influenza caused by viruses adapted to birds.. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is a phrase similar to swine flu, dog flu, horse flu, or human flu in that it refers to an illness caused by any of many different strains of influenza viruses that have adapted to a specific host.