Spotlight

Preventing avian influenza

24 November 2017

Each spring and autumn, there are mild outbreaks of bird flu (avian influenza, AI) on poultry farms in the Netherlands. This is especially true of free-range farms, where animals have access to outdoor areas. Wageningen University & Research (WUR) is studying how to prevent chickens and other poultry from becoming infected.

Preventing avian influenza infections is important for several reasons. Firstly, animals fall ill. Given that they easily infect one another, an entire farm can become sick in no time and animals may die from the disease. Secondly, the H5 and H7 subtypes of the avian influenza virus can develop from a mild variant into a far more dangerous one. The more often the virus is transmitted, the faster a small, random variation can arise in its genetic material (a mutation) that can be more pathogenic. Highly pathogenic viruses are referred to as more ‘virulent’ viruses. And thirdly, some variants of the highly pathogenic avian influenza flu virus can be transmitted from poultry to humans.

The fact that free-range poultry is especially vulnerable does not mean that it is better for chickens to stay indoors.

Waterfowl: a natural source of avian influenza

There are many different mild variants of the avian influenza virus, and wild waterfowl carry them all. Waterfowl, therefore, are a natural source of the mild avian influenza virus. Mild variants of avian influenza, however, do not cause wild waterfowl to sicken.

Highly pathogenic avian influenza viruses are only found in wild waterfowl in exceptional cases. Because highly pathogenic avian influenza does not always sicken the wild birds, they can carry the virus over longer distances. And this is how the Netherlands was hit in November 2016 by H5N8, a highly pathogenic variant of the avian influenza virus. Initially, dead wild waterfowl were found across the Netherlands, after which several poultry farms became contaminated. Studies by Wageningen Bioveterinary Research (WBVR) have demonstrated that the H5N8 virus arrived in the Netherlands via migratory birds. Wageningen Bioveterinary Research is the designated institute where laboratory tests are conducted to determine whether the virus is present in animals. The migratory birds mainly concerned waterfowl, such as all manner of ducks (e.g. widgeons and tufted ducks).

Video about the prevention of bird flu (English subtitles possible)

Transmitting avian influenza

The question remains as to how the avian influenza virus is transmitted from wild waterfowl to chickens, ducks and other poultry. WUR scientists are currently researching the methods of transmission of the virus.
Preventing avian influenza
For poultry, 80% of the cases of avian influenza involve free-range farms. Yet the initial research findings indicate there is no direct contact between waterfowl and chickens; there are no odd ducks wandering among the free-range chickens. Wild waterfowl only visit free-range farms in the spring and autumn. And even then, they only visit when the chickens are inside the barn during the evenings and overnight. The chickens were most likely infected by excrement that the wild waterfowl left on the grounds and in the ponds of the free-range farms. That excrement contains particles of avian influenza virus.

Open water

The fact that free-range poultry is especially vulnerable does not mean that it is better for chickens to stay indoors. Many free-range farms never develop an avian influenza contamination, very likely because they are located in a low-risk area. In high-risk areas, where avian influenza outbreaks occur regularly, poultry farms are located relatively more often at a short distance (less than 500 metres) from waterways like ditches and canals — where wild waterfowl like to congregate — and at a short distance from nature reserves with wild waterfowl.

In addition, all of the poultry farms in the Netherlands that became contaminated during the H5N8 epidemic in the autumn of 2016 had cooped up their animals inside. This ‘cooping up’ was a necessary measure because of the danger posed by avian influenza. The big question remains how, despite this precaution, the virus managed to infiltrate the farms because contact with wild birds was excluded. The virus can be introduced undetected via contaminated materials, shoes or clothing. For this reason, the poultry sector is strongly considering making a hygiene sluice in barns mandatory, so that a potentially contaminated environment can be separated from the ‘clean’ barn housing the chickens. In addition to preventing avian influenza, this also has the significant advantage that it keeps other poultry diseases out of the barn.

Measures for free-range farms

For free-range farmers to keep their flocks healthy, it is especially important to deter wild waterfowl from outdoor areas. This can be accomplished using equipment like laser beams that frighten off birds. Laser deterrence is already common practice for chasing wild birds away from fruit orchards and landfills, offshore oil platforms and drilling operations and airfields. In Australia and the United States, for example, some livestock farms work with specially trained dogs that chase wild animals (birds, but also foxes and other animals) away from free-range farms. The idea to not allow the set-up of new poultry farms in high-risk areas also bears consideration.

Unfortunately, due to the many variants of the virus, vaccinating poultry currently does not provide any relief.

Partitioning may also help to combat avian influenza outbreaks. In collaboration with an entrepreneur, WUR has developed an animal-friendly barn for laying hens: the Rondeel (Dutch). The eggs are available in the supermarket in their characteristic round box that mirrors the shape of the Rondeel barn. The outer edge of the barn is in the open air, and it has mesh-encased roof that partly allows in light. This design protects chickens from the environment while giving them a clear view, and they live in a pleasant and fairly constant climate. They can walk around in peace every day and bathe in the dust, which the animals naturally prefer. The Rondeel eggs have also been awarded the maximum ‘Beter Leven Keurmerk’ score: three stars. That score is as high as what organic eggs are awarded.

Unfortunately, due to the many variants of the virus, vaccinating poultry currently does not provide any relief. During an epidemic, it is nearly impossible to vaccinate more than 100 million chickens in the Netherlands in a short amount of time.

Global One Health

And finally, the Global One Health aspect: the connection between human and animal health. Not only is avian influenza a contagious animal disease, it is also a so-called zoonosis: an animal disease that can sicken humans. Some highly pathogenic strains of the avian influenza virus pose a threat to humans. During the spread of the highly pathogenic Asian avian influenza H5N1 virus at the start of the 2000s in Asia, the Middle East and Africa, hundreds of people died worldwide, primarily from direct contact with infected poultry.

Therefore, preventing outbreaks and further contamination is vital for preventing the suffering of animals, for protecting the income of poultry farmers and for avoiding the mental blow to poultry producers when their farms have to be cleared. And let us not forget that preventing avian influenza is also in the interest of public health.

Further reading

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Armin Elbers

Armin Elbers

Armin Elbers is an epidemiologist and senior researcher at Wageningen Bioveterinary Research. Elbers is analysing the spread of notifiable animal diseases such as swine fever, foot-and-mouth disease and avian influenza, as well as the development of early warning clinical systems to detect these diseases sooner after they have been introduced in the Netherlands. Elbers also conducts field research on midges, horseflies that transmit the bluetongue virus and the Schmallenberg virus to cattle and sheep as well as the African horse sickness virus to equine animals.

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