FAO has published a report on lessons learned from from the fight against highly pathogenic avian influenza in Asia between 2005 and 2011. Since the emergence of H5N1 HPAI in 2003, the disease situation has evolved considerably. At the peak of avian influenza (AI) outbreaks in 2006, 63 countries in Asia, Europe and Africa were affected by the disease; it has now been eliminated from most of these countries. H5N1 is currently entrenched in a number of countries in Asia and the disease is endemic in China, Viet Nam, Indonesia, Bangladesh and large parts of eastern India. A number of countries in Asia, including the Lao People’s Democratic Republic (Lao PDR),Cambodia, Myanmar and Nepal, also experience regular outbreaks.
The period 2004 to 2008 saw a steady decline in disease outbreaks in poultry. While there has been an apparent increase in outbreak numbers since 2009, the 2011/2012 HPAI season saw a significant decline in poultry outbreaks. The last newly-infected country was Bhutan; this outbreak took place in February 2010. However, the disease is known to be under-reported and there is increasing evidence that H5N1 HPAI has become endemic in some of the smaller countries in Asia that have relatively undeveloped poultry industries; such countries include Cambodia and Nepal. It is estimated that the disease has resulted in the loss of over 400 million domestic poultry and has caused economic losses of over US$20 billion.
The information, generated from isolation and genetic and antigenic characterization of a large number of viruses in Asia and other parts of the world, coupled with the information on disease outbreaks, has improved our understanding of the virus’s evolution and the implications for its spread, infectivity and suitability for use in the development of vaccines. The current trends in evolution present a number of concerns, which include the emergence of second-, third- and fourth-order clades, demonstrating rapid evolution and rapid replacement of virus strains in some endemic regions, and the emergence of antigenic diversity, including changes in receptor binding capacity and the ability to break through existing vaccine strains.