Disease: Avian influenza (bird flu)

This page provides general information about  this condition; reveal the text by clicking on  the green headers. Press releases, results from DWHC investigations as well as other useful documents and relevant literature can be found at the bottom of the page.


There are multiple subtypes of the avian influenza virus and these are named according to the nature of two proteins that are present on the surface of the virus: 16 (1-16) different forms of hemagglutinin protein (HA) and nine (1-9) subtypes of neuraminidase protein (NA) are recognised.

Depending on the ability of the subtype to cause disease in poultry (pathogenicity), viruses are further classified as either low or high pathogenic varieties. Mutation can result in a formerly low pathogenic H5 or H7 variant (LPAI) becoming highly pathogenic (HPAI).

Susceptible species

Birds – Water birds, in particular Anseriformes (ducks, geese, and swans) and Charadriiformes (sea gulls, sterns and waders) are the natural reservoirs for LPAI viruses. Typically these viruses do not cause serious disease in birds (Verhagen et al., 2015).

In contrast, HPAI-viruses can cause serious disease and mortality in chickens and other bird sorts including Anseriformes. It Is believed that HPAI viruses develop in domesticated poultry in intensive farming conditions and not in wild birds (Pasick & Kahn, 2014).

Occurrences of HPAI demonstrate that at some point genetic material has been exchanged between HPAI H5N1-virus and an LPAI-virus. This is likely to lead to the development of  HPAI viruses that are better adapted to some species of wild birds which, in turn, would facilitate virus spread by wild birds (Verhagen et al. 2015).

Mammals, including people (AI is a zoonosis), dogs, cats, horses and pigs can become infected with AI viruses.  Additionally, in the winter of 2014-2015 variant H10N7 was found in seals in the Netherlands.



Pasick J, Kahn S. The scientific rationale for the World Organisation for Animal Health standards and recommendations on avian influenza. Rev Sci Tech. 2014 Dec;33(3):691-709.

Verhagen JH, Herfst S, Fouchier RA. Infectious disease. How a virus travels the world. Science. 2015 Feb 6;347(6222):616-7. doi: 10.1126/science.aaa6724.

Signs in animals

Signs in LPAI-infected birds include egg-drop, respiratory problems and an increased mortality rate. Signs are more severe in cases of HPAI infection. In addition diarrhoea, swelling and blue discoloration of the comb, wattle and legs can be seen. In ducks central nervous system signs may occur.

Symptoms in people

People infected with AI develop fluey symptoms including fever, headache, muscle soreness, cough and conjunctivitis.

Infection of people

Infection occurs by direct or indirect contact via the gastrointestinal tract, airways or ocular surfaces.

Preventative measures

Poultry industry – Biosecurity measures to prevent the spread of AI virus are compulsory for poultry farmers and live-animal transporters.

In addition, poultry farms are monitored in order to facilitate the detection of AI infection at an early stage. When AI infection is suspected, infected premises are put under movement restrictions while further investigations are carried out.

Monitoring is also performed in wild bird populations. Surveillance of live birds allows researchers from the Dutch Center for Field Ornithology (Sovon) and the Erasmus Medical Centre, to keep track of which AI viruses are circulating. Europe-wide monitoring of AI in dead birds and living wild birds was instigated after HPAI H5N1 was detected in Europe in 2005 and 2006. It was then associated with mortality in wild birds, particularly the mute (Cygnus olor) and Bewick (Cygnus cygnus) swans.

In the Netherlands the DWHC, Sovon, Central Veterinary Institute (CVI) and the NVWA (Dutch Food and Consumer Product Safety Authority) are involved in this monitoring program.

External information

Research results


No projects found.

Overige berichten


  • Effect of 2020–21 and 2021–22 Highly Pathogenic Avian Influenza H5 Epidemics on Wild Birds, the Netherlands. Caliendo, V., E. Kleyheeg, N. Beerens, K.C.J. Camphuysen, R. Cazemier, A.R.W. Elbers, R.A.M. Fouchier, L. Kelder, T. Kuiken, M. Leopold, R. Slaterus, M.A.H. Spierenburg, H. van der Jeugd, H. Verdaat & J.M. Rijks (2024). Emerging Infectious Diseases. 2024;30(1):50-57. doi:10.3201/eid3001.230970.
  • Zoonotic Mutation of Highly Pathogenic Avian Influenza H5N1 Virus Identified in the Brain of Multiple Wild Carnivore Species. Vreman, S., M. Kik, E. Germeraad, R. Heutink, F. Harders, M. Spierenburg, M. Engelsma, J. Rijks, J. van den Brand & N. Beerens. Pathogens 202312(2), 168; https://doi.org/10.3390/pathogens12020168