WHO has published a long overview: Warning signals from the volatile world of influenza viruses. Excerpt:
The current global influenza situation is characterized by a number of trends that must be closely monitored. These include: an increase in the variety of animal influenza viruses co-circulating and exchanging genetic material, giving rise to novel strains; continuing cases of human H7N9 infections in China; and a recent spurt of human H5N1 cases in Egypt. Changes in the H3N2 seasonal influenza viruses, which have affected the protection conferred by the current vaccine, are also of particular concern.
Viruses in wild and domestic birds
The diversity and geographical distribution of influenza viruses currently circulating in wild and domestic birds are unprecedented since the advent of modern tools for virus detection and characterization. The world needs to be concerned.
Viruses of the H5 and H7 subtypes are of greatest concern, as they can rapidly mutate from a form that causes mild symptoms in birds to one that causes severe illness and death in poultry populations, resulting in devastating outbreaks and enormous losses to the poultry industry and to the livelihoods of farmers.
Since the start of 2014, the Organisation for Animal Health, or OIE, has been notified of 41 H5 and H7 outbreaks in birds involving 7 different viruses in 20 countries in Africa, the Americas, Asia, Australia, Europe, and the Middle East. Several are novel viruses that have emerged and spread in wild birds or poultry only in the past few years.
Some of the outbreaks notified to OIE have involved wild birds only. Such notifications are indicative of the heightened surveillance and improved laboratory detection that have followed the massive outbreaks of highly pathogenic H5N1 avian influenza that began in Asia in late 2003.
Detection of highly pathogenic avian influenza viruses in wild birds signals the need for a close watch over poultry farms. Migratory waterfowl, immune to the disease, are known to spread avian viruses to new areas by quickly crossing continents along the routes of several flyways. These migratory waterfowl subsequently mix with local wild birds and poultry that then become infected.