Facts about avian influenza in humans
Influenza is an infectious disease that primarily presents with respiratory signs and symptoms, caused by RNA viruses. The most significant impacts of influenza viruses on humans are those arising from the influenza A strains. The natural reservoir of influenza A strains is a diverse pool of viruses among aquatic wild bird populations, the avian influenza (AI) viruses. These viruses are divided into those of high and low pathogenicity (hence HPAI and LPAI), according to their severity in the avian species they usually infect. HPAI epizootics continue to be documented worldwide all due to the A/H5 and A/H7 virus groups.
Most but not all of cases of animal influenza in humans have been due to transmission from birds. Many millions of birds have died in huge epizootics either directly from the infection or from culling undertaken to control the infection. Outbreaks have rarely been due to the introduction of HPAI from wild birds, but these do occur. Since 2000 there have been more and larger outbreaks of HPAI in poultry. The reason for this is unknown. Both large and small outbreaks have taken place in Europe.
There are two forms of risk to the health of humans from avian influenza viruses, from infection by the native form of the avian influenza virus and from the potential for the emergence of new pandemic strains either directly from avian viruses, or from their recombination with human or other animal viruses.
The ‘high’ and ‘low’ pathogenicity is not related to the disease in humans. Some avian viruses do not cause disease in humans, or are known to only cause mild disease. Some, however, are known to cause severe disease in humans, for example, A(H5N1). The classification of avian influenza viruses as ‘low pathogenic’ or ‘highly pathogenic’ is defined either by the composition of the cleavage site in the haemagglutinin (HA) gene or by the intravenous pathogenicity index in six-week old chickens in accordance with the criteria listed in Council Directive 2005/94/EC and the OIE International Health Standards .
Any detection of avian influenza viruses of the H5 and H7 subtype in poultry holdings during regular surveillance needs to be notified. Precautionary measures are then applied to prevent potential avian-to-human infection.
The avian influenza virus A(H5N1) emerged in 1996. It was first identified in Southern China and Hong Kong. The A(H5N1) virus kills a high proportion of the poultry that it infects and is therefore known as a highly pathogenic avian influenza virus. It remains poorly adapted to humans. Transmission from birds to humans is infrequent and no sustained human-to-human transmission has been observed, however it can cause severe disease in humans.
The A(H5N1) virus has only sporadically been detected in European poultry or wild birds.
A novel influenza A avian influenza virus, A(H7N9), was identified in China in March 2013, causing severe illness in humans. It was the first time that a low pathogenic avian influenza A virus had been associated with fatal outcomes for people.
Influenza virus detections in poultry in EU/EEA
In 2014 and 2015, outbreaks of highly pathogenic avian influenza virus A(H5N8) in poultry were notified by several European countries. Previously, this virus has been detected among wild birds and domestic poultry in Asia.
In 2015, highly pathogenic avian influenza virus A(H5N1) was detected in poultry and wild birds in Bulgaria and Romania.
In 2015 and 2016, outbreaks of highly pathogenic avian influenza viruses A(H5N1), A(H5N2), and A(H5N9) as well as detections of low pathogenic avian influenza viruses A(H5N2) and A(H5N3) have been reported.
No human infection with these viruses have been reported in EU/EEA countries. The risk of transmission to the general public is extremely low. Persons at risk are mainly those in direct contact/handling diseased birds or poultry, or their carcasses (e.g. farmers, veterinarians and labourers involved in the culling and rendering).
Ongoing monitoring and testing of wild birds and domestic poultry in the EU is important to detect and prevent further spread of this highly pathogenic virus to poultry and other farmed birds.
Questions and answers on avian influenza
What is avian influenza (bird flu)? Why are we concerned about bird flu outbreaks? What are the control measures in birds and animals? How do outbreaks of avian influenza spread?
Factsheet on A(H5N1)
The information contained in this factsheet is intended for the purpose of general information and should not substitute individual expert advice and judgement of healthcare professionals.