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.
Types of Bird Flu (Avian Flu) There are many different subtypes of type A influenza viruses. These subtypes differ because of certain proteins on the surface of the virus (hemagglutinin [HA] and neuraminidase [NA] proteins). Each different combination of HA and NA proteins is a different subtype of the virus.