Avian influenza virus and human: pandemic concern and threat?

Type A influenza viruses causes infections in human and animals, especially in birds. Wild aquatic birds are the natural hosts for all known influenza type A viruses. Avian type viruses are divided into two groups: highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI). HPAI virus is very dangerous, but LPAI virus is much weaker. Two forms of mutations including drift and shift have been recognized for antigenic changes in influenza viruses. Antigenic shift is responsible for producing re-assortment viruses with a potentiality to be transmissible to human and possibly resulting in pandemic. Emerging new species of viruses, the loss of previous immunity in human population and the transmission from human to human are the three major conditions that result in the occurrence of influenza pandemic in human. When pandemic happens, public health is a major concern due to probability of high fatality rate and other socioeconomic consequences.