12.03.2015

Highly Pathogenic Avian Influenza (HPAI) was confirmed on the 16th November 2014 on a duck breeding site in Yorkshire, which was designated as the infected premises. The infected premises were part of an integrated duck breeding and growing operation encompassing pedigree breeding through to commercial duck meat production, with 43 associated sites mainly situated in the Midlands or north of England. The company covers approximately half of annual UK duck production, and has a wide export market for its elite stock.
The virus that caused the outbreak is strain H5N8 HPAI, which is the same strain, with close sequence similarity, as that found in the outbreaks in the same time period in Germany in turkeys and ducks, in the Netherlands in chickens and ducks, and in Italy in turkeys. The same strain was recovered in a similar time frame from two (healthy) wild birds shot in Germany, from the faeces of wild birds in the Netherlands, a wild bird in the Russian Federation and has also been identified in apparently healthy wild birds, captive birds of prey fed on hunter killed wild birds and in an outbreak in a mixed backyard flock in the USA. The H5N8 HPAI virus has also been reported as the cause of many poultry outbreaks in East Asia in the past twelve months. The infected premises virus has been fully sequenced and the results suggest that it is still predominantly an avian-adapted virus, without any specific increased affinity for humans.
The most likely time that infection was estimated to have entered the infected flock is between 24th October and 6th November 2014. Initially there was uncertainty as to whether the other flock on the premises (‘Site 1’, which was routinely depopulated on 5th and 6th November 2014), was also infected. A significant drop in egg production had been noted in this flock before depopulation but this could have been due to routine management practices implemented to prepare the birds for slaughter. Further analysis of production and mortality data and initially negative PCR test results from eggs and feathers from this flock found that there was no conclusive evidence to suspect HPAI infection in these birds prior to depopulation and it was concluded there was a low probability that the flock was infected. However, early stage infection could not be ruled out, so the maximum precautionary tracing window up to the 8th October 2014 (21 days before the start of the egg drop observed on Site 1) was applied. Subsequently, further experimental analysis carried out on the feather samples yielded a positive result, implying that early stage HPAI infection was present in the flock before depopulation.
There is substantial uncertainty as to the source of infection for the infected premises, however all the available evidence suggests that indirect contact with infected wild birds (for example via their faeces) is the most likely source.
This assessment is based on: evidence that no poultry were brought onto the infected premises during the source window; that there is no evidence of infection in poultry in the local area; that there is no evidence of a direct industry-related connection to the cases in Germany, the Netherlands, Italy, USA or East Asia; the time of year of these outbreaks occurred with respect to wild bird migratory movements and the finding of this strain of virus in healthy wild birds in multiple countries are both supportive of a wild bird mediated introduction. Additionally the absence of other cases having been identified in the UK provides supporting evidence.
There are extensive personnel and other contacts within the company and the industry, and the ability of the virus to cause few clinical signs in ducks raised the possibility that one or more associated duck premises were silen