Avian influenza A virus infections in humans: current knowledge to enhance host innate immunity to control Avian influenza

Abstract Every year, ~500,000 people die because of influenza A virus infections, with many more suffering from nonfatal infections. The ancestral host of influenza A viruses is recognized as wild birds, and avian viruses have contributed genetic material to the majority of human viruses, including subtypes H5N1 and H1N1. Thus, influenza virus transmission in wild and domestic animals, as well as humans, is intertwined. Human populations have suffered a high death toll because of influenza pandemics caused by viruses with new antigenic subtypes. The most lethal pandemic, the so-called Spanish influenza of 1918 to 1919, was caused by an H1N1 virus and killed at least 20 million people worldwide. Moreover, the number of affected countries increased between 2003 and 2008, beginning in East and Southeast Asia and progressing to West Asia and Africa. Evidence indicates that viral transmission in domestic poultry, spread to other domestic animals, wild birds, and humans, and the potential for pandemic spread are all on the rise. Phylogenetic studies of viral genes have revealed species-specific lineages as well as genes that have crossed species barriers, indicating the threats of influenza A virus outbreaks in humans is continuous. In this review we try to provide a perspective on the outbreaks, detrimental factors, innate immune responses, and advances in detection and diagnosis for better control and management of influenza virus A outbreaks.