Avian influenza or bird flu falls under two groups. Low pathogenic avian influenza affects wild birds as well as domestic poultry, where minor symptoms to no sign of infection are exhibited.
Generally, these low-mortality strains pose an insignificant threat to human health. However, the H5 and H7 strains can possibly mutate into a highly pathogenic avian influenza. Highly pathogenic avian influenza spreads rapidly and has recorded a high death rate in birds. It's rarely transmitted to humans, but when a person gets infected, death can be inevitable.
H5N1 is the deadliest of the very few avian flu viruses that have crossed the species barrier with the ability to infect humans. Infected individuals have reportedly come in contact with infected poultry or contaminated surfaces with traces of bird secretions/excretions.
The spread of avian influenza among humans has been limited to rare, sporadic cases since February 2007. Influenza H5N1 virus remains under close monitoring. Scientists do not disregard the potential of the avian virus strain with a high mortality rate to evolve. Mutation could have the virus easily transmitted among non-immune people and ultimately lead to a dreaded pandemic.