The H5N8 variety of avian influenza virus, which hit hard in Korea earlier this year, is now raising alarm among European poultry owners, with an outbreak detected in the Netherlands and a probable one reported in Britain over the weekend, following one in Germany earlier this month.
The virus, which has never been reported to infect humans, may have used wild birds to catch a ride from East Asia to Europe, European authorities and the United Nations Food and Agriculture Organization (FAO) said today.
Dutch outbreak involves 150,000 birds
In the Netherlands, the virus killed 1,000 of a flock of 150,000 layer and breeding hens in Utrecht province, veterinary authorities said in a report to the World Organization for Animal Health (OIE) today. The rest of the flock has been destroyed to prevent any further spread. The European Commission (EC) in a statement today said the flock is housed indoors.
In response to the outbreak, Dutch authorities announced a 72-hour ban on transportation of poultry products, including birds, eggs, dung, and used straw among poultry farms across the country, which is the world's leading egg exporter, according to a Reuters report yesterday.
The story said the movement ban would continue for 30 days for poultry farms within 10 kilometers of the outbreak site, and all would be subject to enhanced security measures. The OIE report said there are 13 other farms within that zone.
H5 virus reported in Britain
In the United Kingdom, officials reported to the OIE that a highly pathogenic H5 virus killed 338 birds on a Yorkshire farm housing 6,000 60-week-old breeding ducks.
"The birds showed signs of slightly raised mortality and a gradual but marked drop in egg production," said the report, filed today. "An underlying bacterial/fungal infection is likely to have preceded the infection by avian influenza contributing to presentation of clinical signs."
The report said the surviving birds would be destroyed to stop the virus, and the farm would be disinfected.
"The information available indicates that the H5 virus in the UK is probably identical to the H5N8 HPAI virus found in The Netherlands and in Germany," the EC said in its statement today.
The UK Department for Food, Environment & Rural Affairs (DEFRA) said the virus has been identified as an H5 subtype and that H5N1 has been ruled out, with further tests under way to identify the exact subtype and strain. The agency asserted that the risk to human health is very low and that there is no risk to the food chain.
The EC said both the UK and the Netherlands are taking a set of control measures specified in European Union regulations, including a temporary ban on the sale of poultry and poultry products to other countries.
H5N8 in Europe
The Dutch and British outbreaks, which both began Nov 14, surfaced 10 days after H5N8 first surfaced in Europe with an outbreak on a turkey farm in northeastern Germany. That outbreak, in the state of Mecklenburg–Western Pomerania, infected 5,000 turkeys and killed 1,880, prompting culling of the rest of the 31,000-bird flock.
The FAO, in a statement today about the German outbreak, said genetic information from German authorities shows the virus is very similar to isolates identified earlier this year in China, South Korea, and Japan. South Korea was hit by a series of outbreaks that started in January and by mid-March had forced the destruction of more than 10 million birds, 6% of the country's poultry.
Outbreak data from South Korea and Germany show that the H5N8 virus causes high death rates in chickens and turkeys, but experiments with the Korean strain suggests it does not cause high mortality in domestic or wild ducks, though ducks shed the virus, the FAO said.
The genetic link between the Korean and German isolates and the fact that wild ducks may be infected without dying "could suggest a role for wild birds in the spread of the virus over long distances and further onward transmission to poultry," the FAO said.
Wild birds were linked previously to the spread of H5N1 virus from Asia to Europe and Africa starting in 2005, the agency said, adding, "With regard to H5N8, experts hypothesize that the virus may have travelled during the spring season from eastern Asia into the breeding grounds of migratory birds in Central Asia. These migratory birds may now be carrying the virus with them as they migrate into more moderate climates."
The EC also favored the wild-bird hypothesis, commenting, "The fact that the three recent outbreaks in Germany, The Netherlands and the UK have occurred in proximity of humid areas with wild birds and the absence of any other possible epidemiological link between them point towards wild migratory birds as a possible source of virus. A species of wild swans might be carrying the virus without showing signs of disease."
The FAO said the detection of H5N8 in Europe "is a reminder that avian influenza viruses still represent a global threat to animal health and the international poultry industry. FAO is calling for worldwide vigilance and targeted surveillance as well as optimized biosecurity measures on farms."
Nov 16 OIE report of Dutch H5N8 outbreak
Nov 17 European Commission statement
Nov 17 Reuters story on Dutch H5N8 outbreak
Nov 17 OIE report of UK H5 outbreak
Nov 17 BBC News story on Dutch and UK outbreaks
Nov 17 UK DEFRA statement
Nov 14 FAO statement on H5N8 in Germany
Nov 6 CIDRAP News item on German outbreak
Mar 14 CIDRAP News item on H5N8 toll in South Korea