Europe is once again experiencing epidemics of bird flu, the deadliest animal disease known. While the disease may be milder in ducks and geese, it seems inevitable that more than 90% of the flock in affected chickens and turkeys will die within a few weeks.
Bird flu outbreaks are caused by avian influenza viruses, which cause mild infection in most birds. But two subtypes (called H5 and H7) stand out as a very deadly virus.
Influenza viruses have a high mutation rate and can exchange genes when two viruses infect a single host at the same time. These genetic changes allow them to change their structure and evade their host’s immunity and continue to spread.
In the previous century, outbreaks of deadly avian flu were rare and were always caused by mild H5 or H7 viruses that turned into a deadly virus when infecting a flock of chickens or turkeys. By 1996, emerging outbreaks were either effectively controlled or dwindled due to a lack of susceptible hosts.
H5N1 Appears
Infections caused by these deadly viruses have not been observed in wild birds. But the situation changed after the H5N1 virus appeared in China. Outbreaks in poultry were not effectively controlled. The virus gradually expanded its reach to China and from 2003 to Asia and Africa. People who were in close contact with infected poultry also began to become infected, resulting in the death of 456 people to date. In other words, bird flu has become a threat to humans as well.
Wild birds became infected due to a transmission resulting from the continued spread of the virus in poultry. This led to new H5 viruses that are still deadly to poultry but do little harm to certain waterfowl species. As a result, migratory waterfowl were able to spread the viruses over great distances by flying thousands of kilometers despite carrying these viruses.
In 2005, wild waterfowl first introduced the virus to Europe during their autumn migration. This was the first sign that the ecology of these viruses had completely changed; A virus closely related to poultry had adapted itself to wild waterfowl, greatly increasing their survival potential.
In the spring and summer each year, waterfowl congregate at their breeding grounds in Siberia and confuse influenza viruses, creating new variants that they then bring to Europe, Asia and Africa during their autumn migration, causing deadly outbreaks in poultry.
Predictably, there isn’t much we can do to control infections in wild waterfowl. Inspections to assess the risk of exposure to the virus to poultry and to remove the bodies of dead birds from the environment are among the recommendations offered.
Poultry breeders in areas with many waterfowl during the winter are advised to keep their poultry indoors and take biosecurity measures to keep the virus out of their sheds. The droppings of infected wild birds can contain large amounts of the virus and are easily transmitted to poultry by uncleaned boots or equipment.
Existing biosecurity programs have not been effective enough to prevent infections in risk areas. There were more than 1,000 outbreaks in the EU alone in the 2020-21 season. In the current season, dozens of epidemics have already been detected.
Recurrent annual epidemics, often resulting in mass killings of poultry, pose a clear threat to the sustainability of poultry farming.
A vaccine can be a tool to help solve the problem. However, it is banned in many countries and its use creates trade barriers for poultry. Trade barriers are because most of the vaccines available prevent disease, but do not stop the transmission of infection.
A vaccine that stops disease but does not stop transmission can lead to “silent” virus spread, which compromises epidemic control and is undesirable because the virus has the potential to spread from animals to humans.
Fortunately, most of the currently circulating H5 virus variants are not as dangerous as their H5N1 ancestor, which was once a major problem for humans. However, caution is needed as this can easily change due to the virus’s ability to alter its genetic code. In other words, it is necessary to take measures to prevent a new risk of H5N1 for humans.
For poultry, the immediate development of effective vaccines is seen as the only sustainable solution. Next-generation vaccines may have greater potential to control avian influenza, but their effectiveness in stopping virus transmission must be demonstrated in the field. Such vaccines will not only protect poultry, but also minimize human exposure to the virus. . .
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