Avian influenza, better known as bird flu, is a highly contagious viral disease affecting both wild and domestic birds, and is one of the most important diseases in the poultry industry. The natural hosts of avian influenza are wild birds, especially waterfowl. Avian influenza is classified into two categories depending on the severity of the disease in domestic birds: low pathogenic and highly pathogenic avian influenza (LPAI and HPAI, respectively). HPAI is included in the list of notifiable diseases of the World Organisation for Animal Health (OIE) and causes high mortality rates in domestic birds or vulnerable wild species. 

Although HPAI are viruses that primarily affect birds, they sometimes cross the species barrier and infect other mammalian species, including humans. Avian influenza viruses have been key in the different influenza pandemics and represent an important zoonotic risk. Specifically, the HPAI H5N1 subtype was first detected in birds in 1996 in Guangdong (China) and the first human case was identified in 1997. Since then, the HPAI H5N1 subtype has had a major impact on the poultry industry and around 900 human cases have been detected with a mortality of 50-60%. Until now, no human case of HPAI H5N1 has ever been detected in Spain and new infections cannot be ruled out. Human infections with HPAI H5N1 are due to close contact with infected birds and the risk to the general population is considered low, as no sustained inter-human transmission has been detected.  

However, the unprecedented number of outbreaks of avian influenza in the 2021-2022 season in Europe and worldwide, obliges us to keep a close eye on how the situation is evolving and to continue active surveillance to mitigate the impact of the virus on the poultry industry and to be able to anticipate future pandemics. We must remember that the next influenza pandemic is not likely, it is almost certain. So it is not a question of whether it will happen or not. The question is when it will happen and how it will originate.

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