A study by Wageningen Bioveterinary Research (WBVR) has shown that the 'new' HPAI H5N8 virus – detected in October 2020 in mute swans in the Netherlands – shares a common ancestor with viruses that were last reported in Egypt in 2018-2019. The new H5N8 virus also has a similar genetic composition. WBVR has investigated the relationship between the viruses in more detail. Notably, the virus is not directly related to the European H5N8 viruses that were identified in the first half of 2020.
Genetic analysis of the avian flu virus detected in October in the Netherlands suggests that the ancestor of this H5N8 virus has been circulating in Egypt since March 2017 and caused outbreaks there in 2018-2019. After these outbreaks, the virus went unreported until it was detected in the Netherlands in October 2020. This H5N8 introduction is not related to outbreaks in Eastern Europe, Germany and Bulgaria that occurred earlier in 2020. It also seems unlikely that the H5N8 virus has been circulating unnoticed in the Netherlands in the wild bird population since 2017.
Mute swans do not migrate over long distances, so the virus may have been introduced by other waterfowl species that migrate from their breeding grounds in northern Russia to wintering grounds in the Netherlands. Prior to the bird migration season in 2020, no highly pathogenic avian influenza (HPAI) H5N8 viruses or deaths in wild birds from these breeding grounds were reported. Beginning in August 2020, however, there were several reports of HPAI H5N8 viruses being found in wild birds and poultry in southern Russia and northern Kazakhstan.
The sequences of the viruses detected in Russia and Kazakhstan have recently been published, and these suggest a genetic relationship between these viruses and the HPAI H5N8 virus in the Netherlands. Some waterfowl species, such as wigeon, tufted duck and white-headed goose, are known to reside in these regions of Russia and Kazakhstan, from where they migrate to wintering grounds the Netherlands. The HPAI H5N8 virus was detected in a wigeon found near the location of the dead mute swans, which suggests that the wigeon may have introduced the virus to the Netherlands. The virus has also been detected in various species of geese, such as barnacle geese and greylag geese, that also migrate to the Netherlands from their breeding grounds in Russia.