On 20 October, Wageningen Bioveterinary Research (WBVR) tested two dead mute swans positive for highly pathogenic H5N8 avian influenza. This was the first case of bird flu that was discovered in the Netherlands in 2020.
This news has been last edited on Monday 2 November.
Various wild birds with bird flu
The two swans sent to WBVR were part of a group of six swans found dead in the Netherlands’ Groene Hart region, near Kockengen. Since then, WBVR detected highly pathogenic avian influenza of the type H5N8 in several dead wild birds found in the provinces of Utrecht, Noord-Holland, Noord-Brabant and Friesland. It concerned different bird species, such as mute swan, greylag goose, barnacle goose and wigeon.
H5N8 virus and bird migration
H5N8 virus was detected in dead mute swans in Western Russia in August and was later found in a tufted duck and mallard as well. The virus was then detected in dead wild birds in Kazakhstan in September. H5N8 was found in swans at a zoo in Jerusalem (Israel) in October. Wild migratory birds can bring the virus from these areas to Europe during their autumn migration. However, H5N8 viruses have yet to be reported along the migration routes towards the Netherlands from countries to the east.
It is particularly striking that the H5N8 virus was detected in dead swans in Russia, Israel, and now the Netherlands. Swans may be very sensitive to this specific virus, but this will have to be investigated further. The wild mute swan populations in Russia are known not to migrate to Europe for hibernation. The virus was probably introduced to the Netherlands through other bird species, after which local bird populations became infected. This suggests that the virus is circulating locally among wild birds in the Netherlands. No dead birds from other areas in the Netherlands have been tested as of yet, so it is unclear whether the virus has spread further.
Risk of introduction to poultry
The H5N8 virus can spread from the wild bird population to poultry farms, in particular through faeces from wild birds infected with the virus. The current risk of introducing highly pathogenic avian influenza into the poultry sector is therefore high, especially in areas with many wild waterfowl. Biosecurity and vigilance with regard to clinical signs of avian flu in poultry farms are of great importance at the moment for preventing avian influenza outbreaks.
Genetic composition of avian influenza viruses
Highly pathogenic avian influenza viruses were previously introduced to the Netherlands by wild migratory birds, after which several poultry farms became infected. In 2014 this involved an H5N8 avian influenza virus, and in 2016 it also concerned an H5N8 avian influenza virus, but with a different genetic composition. The H5N6 virus was introduced to the Netherlands in 2017. WBVR will conduct further research to determine the sequence of the entire virus genome. This should reveal how this new H5N8 virus is related to other highly pathogenic avian influenza viruses currently circulating.
Dead wild bird monitoring programme
The dead wild bird monitoring programme is of great importance for the rapid detection of highly pathogenic viruses in the Netherlands. This programme also makes it possible to monitor the further spread of the virus among wild birds in the Netherlands. Wild birds found dead can be sent in to be tested for infection with avian influenza.