Bird flu (avian influenza, AI) is a collective term for different influenza viruses that may be dangerous to poultry. Especially chickens, turkeys, waterfowl, waders, beach birds, ratites and starlings are susceptible to avian influenza, with possible lethal consequences. Some variants of avian influenza are also transmissible to humans.
Mild and hazardous avian influenza
Avian influenza has two variants: a mild variant and a hazardous variant. Most viruses are the mild variant, known as Low Pathogenic Avian Influenza (LPAI). On average about 10 to 30 introductions of the mild variant are detected annually. Birds that have been infected with this variant exhibit few disease symptoms. However, the mild form may also change into the highly contagious variant, known as High Pathogenic Avian Influenza (HPAI). It is for this reason that companies are also culled in the case of an outbreak of a mild variant.
Wild birds are often the source of avian influenza viruses. Birds, including poultry, can catch bird flu in several ways:
- through direct contact with infected birds; the virus can be spread through the respiratory system, eye fluids and droppings;
- through contaminated materials such as food, crates, vehicles and people who have been in contact with the virus through their shoes or clothing;
- via dust from a contaminated coop (spread through the air).
In some cases people – and other mammals like pigs and foxes – can become infected with avian influenza. This can happen if there is direct and extensive contact between infected animals and humans, like the caretakers of the animals or those involved in culling.
The symptoms of avian influenza in humans are very mild in most cases. Serious or even fatal infections have only been reported in exceptional cases. This happened for example after infection with the HPAI H5N1 virus in Asia in 1997 and 2004, with a HPAI H7N7 in the Netherlands in 2003 and recently with a LPAI H7N9 virus in China.
The avian influenza virus can enter the Netherlands through the import of live birds, eggs and egg products, poultry and poultry products as well as through travellers. Spreading via migratory birds also represents a risk.
Free-range poultry farms in the Netherlands are at greater risk of avian influenza infection, because the poultry can come into direct contact with potentially infected wild birds and waterfowl.
There is a fear that the avian influenza virus will change to make it easily transmissible among humans. This could lead to a worldwide influenza epidemic; a pandemic. Whether this will actually happen is unpredictable. Previous flu pandemics were the Spanish flu (1918), with an estimated 40 million deaths worldwide, the Asian flu (1957-58) and the Hong Kong flu (1968) with 2 to 3 million victims each.
Within the European Union legislation exists to prevent avian influenza from being introduced or spread throughout the EU via infected poultry or transport. For example, farmers and transporters of live animals must take hygienic measures to prevent infection and the spread of the avian influenza virus.
Monitoring and early warning program
The Netherlands has operated a monitoring program since the HPAI H7N7 outbreak in 2003. Domestic poultry, but also wild birds, are regularly checked for antibodies to the virus. In this way, it is possible to discover avian influenza at an early stage and limit the spread of the virus (early warning programs).
Vaccination of poultry?
Vaccination of poultry is possible but there are many snags. It is costly, difficult to organise and tied to permits. Some buyers of Dutch poultry products (including Germany) do not want products from vaccinated animals.
The Wageningen Bioveterinary Research (WBVR) is the designated institute where the diagnosis of the disease Avian Influenza or avian flu is performed.
Laboratory tests are performed at WBVR to see if the virus is present and diagnostics are run on samples of poultry from locations where a suspicion of the disease is present. WBVR also examines wild birds and waterfowl. These birds are often reported by individuals and retrieved by the GD (municipal services) and AID (general inspection). This is done at the request of the government in order to rule out avian influenza as a cause of the birds’ death. The goal is to identify the disease as early as possible and then check the poultry kept in the neighbouring areas.
The duck genome and transcriptome provide insight into an avian influenza virus reservoir species
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Systemic distribution of different low pathogenic avian influenza (LPAI) viruses in chicken
Virology journal 10 (2013). - ISSN 1743-422X - 7 p.
Rate of introduction of a low pathogenic avian influenza virus infection in different poultry production sectors in the Netherlands
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Rapid emergence of a virulent PB2 E627K variant during adaptation of highly pathogenic avian influenza H7N7 virus to mice
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Quantification of dust-borne transmission of highly pathogenic avian influenza virus between chickens
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Public Interests and Values in Multi-Level Food Risk Governance: European Responses to Avian Influenza
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Guiding outbreak management by the use of influenza A(H7Nx) virus sequence analysis
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Global lack of flyway structure in a cosmopolitan bird revealed by a genome wide survey of single nucleotide polymorphisms
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