Bird flu, refers to “influenza caused by viruses modified to birds. Of greatest concern is highly pathogenic avian influenza (HPAI).

“The Bird flu” is a expression like to “human flu” in that it refers to an illness caused by any of many special strains of influenza viruses that have modified to a specific host. All known viruses that cause influenza in birds belong to the species influenza A virus. All subtypes (but not all strains of all subtypes) of influenza A virus are adapted to birds, which is why for many purposes avian flu virus is the influenza A virus

Version is non-exclusive. Organism adapted towards a particular species does not prevent adaptations, or partial adaptations, towards infecting different species. In this method strains of influenza viruses are adapted to multiple species, though may be preferential towards a exacting host. For example, viruses answerable for influenza pandemics are adapted to both humans and birds. Recent influenza research keen on the genes of the Spanish flu virus shows it to have genes adapted to together birds and humans; with more of its genes from birds than less deadly later pandemic strains.

The Pandemic flu viruses have some avian flu virus genes and frequently some human flu virus genes. Both the pandemic strains limited genes from avian influenza viruses. The new subtypes arose in pigs confected with avian and human viruses and were soon transferred to humans. Swine were painstaking the original “intermediate host” for influenza, because they supported resentment of divergent subtypes. However, other hosts appear capable of similar confection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible. The Spanish flu virus strain may have been transmitted directly from birds to humans.