Avian Flu

Avian flu means "flu from viruses adapted to birds", but is sometimes mistakenly used to refer to both other flu subsets (such as H5N1 flu) or the viruses that cause them (such as H5N1).

"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 flu viruses such that the strain in question has adapted to the host. "Avian flu" differs in being named after an entire vertebrate class with 8,800–10,200 species. All known avian flu viruses belong to the species of virus called Influenza A virus. All subtypes of Influenza A virus are adapted to birds, which is why for many purposes avian flu virus is the Influenza A virus.

Adaptation is sometimes partial or multiple so a flu virus strain can be partially adapted to a species or adapted to more than one species. Flu pandemic viruses are human adapted and also bird adapted. Being adapted to one species does not mean another species can not catch it; nor does it mean it can not adapt to another species.

...More at Wikipedia 

Related Links:

• US National Library of Medicine
• Mayo Clinic

Recent Hope Cube Blog Entries For Avian Flu