Abstract
Avian influenza is a disease caused by influenza A virus (IAV) that mainly affects domestic poultry but poses a serious zoonotic threat due to direct transmission from poultry to mammals including human beings. While the high pathogenic avian influenza (HPAI) mainly caused by H5 and H7 subtypes of IAVs lead to high mortality, the low pathogenic avian influenza (LPAI) caused by all the 16 haemagglutinin subtypes lead to high production losses. Wild aquatic birds serve as reservoir hosts as the virus cause productive subclinical infections in them. Reported for the first time in 1878 in Italy, the IAVs have so far caused three pandemics in humans. The H5N1 virus currently circulating for over two decades throughout the world has caused outbreaks in over 60 countries including India. LPAI viruses are transmitted amongst terrestrial poultry via respiratory droplets and aerosols and the HPAI viruses are transmitted via faecal route. Pathogenesis of IAVs is markedly different between wild water birds, terrestrial poultry and humans. Clinical diagnosis of AI is very difficult and often confused with other respiratory diseases of poultry. Diagnosis of AI involves isolation, identification and characterization of the virus. Current molecular techniques particularly the RT-PCR and real-time RT-PCR are recommended for rapid AI diagnosis. Effective control programs for avian influenza in poultry farms or its spread between farms can reduce the loss due to the disease by a minimum of 75%. The various control measures along with their advantages and disadvantages are discussed in detail in this chapter.