In December 2017, the highly pathogenic avian influenza (bird flu) broke out on a duck farm in Biddinghuizen. The farm reported various symptoms of disease and a high mortality rate. A few days later, several dead swans and a single dead tufted duck were found near the Veluwemeer. Then, in December 2017 and January 2018, two hobby farms were also infected with the virus. Wageningen Bioveterinary Research (WBVR) examined samples from the duck farm, the hobby farms and the wild birds, and concluded that this was a new virus subtype, H5N6.
A new bird flu virus, H5N6
The H5N6 subtype had been discovered earlier in 2017, in Greece and various countries in Asia. We know that several H5N6 virus strains occur in Asia that can infect humans. WBVR genetically tested the virus and revealed that the Dutch strain is not related to the human H5N6 viruses in Asia. Further research, such as infection tests on mammals (ferrets), could provide more insight into the risks for humans. To date, no humans have been infected with the Dutch H5N6 virus strain. The genetic analysis also revealed that the viruses found in the wild birds are very similar to the virus on the infected duck farm. Infected wild waterfowl probably brought the virus close to the farm, after which it somehow found its way into the barn.
Genetic relationship between H5N8 and H5N6
The genetic study revealed that the H5N6 virus is related to the H5N8 strain that infected several poultry farms in the Netherlands in 2016-2017, and also killed many wild birds. The H5N8 virus obtained a new NA gene through the exchange of genetic material with other viruses, resulting in the subtype H5N6. Different strains of bird flu often exchange genetic material, which is known as reassortment. This reassortment process probably took place on breeding grounds in Siberia, where many wild birds come together, after which the new H5N6 virus was carried to the Netherlands with migrating flocks.
H5N6 in Europe
In late December 2017, H5N6 was discovered in a dead wild bird in Switzerland. In January, the virus was also found in a wild duck in Germany and in several dead wild birds in the UK, and later in two larger groups (70) of dead wild birds. However, the current bird deaths cannot be compared to the H5H8 epidemic of 2016-2017, when mass mortality occurred among wild waterfowl. Many commercial poultry farms all over Europe were hit by the bird flu epidemic of 2016-2017. The new H5N6 virus has only infected one commercial poultry farm in the Netherlands so far. However, the number of reports of H5N6 in Europe is increasing, so this H5N6 strain seems to be spreading.