British bird flu isolated but not in isolation

Source of the latest H5N1 outbreaks is proving illusive to identify but most likely could be wild birds.

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Virus sub-type was identified as H5N1 of the highly pathogenic avian influenza (HPAI) virus, and 29,000 premium free-range turkeys, geese and ducks culled across five East Anglia farms run by the prestige United Kingdom (UK) poultry producer, Gressingham Foods. Flocks on four out of the five farms were culled according to UK government’s ‘slaughter as a precaution’ policy due to ‘dangerous contact’ because all five units had shared the same pool of farm staff. Now comes the hard part for UK government’s Department of Environment, Food and Rural Affairs (DEFRA) to discover source of the second H5N1 outbreak in less than one year.

Early this year, Bernard Matthews’ site at Holton is the benchmark where migratory wild birds were initially blamed for introducing H5N1 into the UK. Infection was subsequently found to have arrived on partly processed turkey meat from Hungary brought in by the Bernard Matthews company. That time, genetic sequencing pointed the finger of blame firmly at Hungary and Bernard Matthews Company so perhaps it is worth first considering the poultry trade for this outbreak too. 

For the current outbreak, comments by UK’s acting chief veterinarian, Dr Fred Landeg, suggest the virus is genetically close to that responsible for outbreaks in wild birds (France, Germany and Czech Republic) and poultry (Czech Republic – turkeys and chickens; Germany – ducks) this summer.

Poults sourced from UK

In press releases, Gressingham Foods claims that all turkey poults and feed are sourced from UK producers, although a report that day-old ducklings are regularly imported from the Netherlands has not been denied. Ducks were grown on the infected Redgrave Park Farm but Gressingham Foods say these Pekin ducks were all hatched and raised in the UK. There are few willing to believe or bet on Dutch ducks infected with H5N1 and subsequent testing at Redgrave Park Farm has given ducks and geese a clean bill of health. Only turkeys were infected. Focus is on trucks and drivers exporting ducks to UK to discover whether any history of contact with at risk areas in Germany or Czech Republic.

According to Expatica Netherlands, Dutch transport of day-old duck chicks into UK was stopped because it may have carried AI into eastern England. Investigative focus is on trucks and drivers because authorities fear possible connection with H5N1 outbreaks in Germany and the Czech Republic. Dutch farm ministry said there has only been one recent shipment into the UK and that to a farm some 50km away from Redgrave. Gressingham Foods (via its subsidiary, Redgrave Poultry) claims no knowledge of direct links with the Netherlands and the five farms involved.

They were commenting on reports that first appeared in The Times (15 November 2007). This claimed the UK virus was almost identical to that found in ducks in southern Germany and the Czech Republic in June-August 2007, implying transference via equipment, vehicle or human contagion. Imports of speciality poultry meats by Gressingham Foods are also part of overall investigations, claimed The Times. Imported meat – guinea fowl, poussin, Barbary duck, duck breast and legs and smoked duck breasts – is frequently processed or packed at the company’s plant just 1km from the Redgrave Park Farm near Diss on the border between the countries of Suffolk and Norfolk. An audit trail is being followed to see if any imported meat came from European farms near recent outbreaks of H5N1. 

Did migratory birds bring infection?

If this line of investigation comes to a dead end, a potentially more serious wild bird source looks likely. East Anglia is a haven for wild waterfowl and huge numbers arrive every year from the continent to escape harsher winter conditions in Europe and to feed in the expanses of water, reed beds and marshland of East Anglia. Redgrave Park itself has a large ornamental lake where wild waterfowl including geese, swans and ducks reside. 

This autumn’s migratory season is near its end, and ornithologists at Royal Society for Protection of Birds (RSPB) say there are no finds of dead birds with H5N1 in East Anglia or back into Europe since the French, German and Czech cases this summer.

Infection already endemic in wild birds?

The other and even less palatable wild bird source is endemic infection in the UK wild bird population. Wild birds were not involved in the introduction of H5N1 into the UK in February 2007 but seagulls were implicated in the transfer of infection from discarded Hungarian-sourced turkey waste from the processing plant to turkey growing sheds adjacent on the Bernard Matthews’ site at Holton in Suffolk. Seagulls were seen scavenging waste and carrying turkey breast trimmings onto turkey house roofs that were subsequently found to be leaking.

Some might argue that any wider and longer wild bird risk should be low because wild waterfowl like ducks, wild geese and swans were not involved.  But long gone are the days when seagulls like black-headed gulls (Larus agentatus) and herring gulls (L. ridibundus) were birds only of the seashore.  Huge colonies of gulls permanently feed and breed around livestock farms, sewage farms, landfill sites and marshland. Gull chicks hatch, grow, mature, breed and die without ever seeing the sea. These inland gulls mix and compete for food with mallard ducks (Anas platyrhynchus), wild geese (Anser spp.) and mute swans (Cygnus olor) on reservoirs, lakes and ponds in public parks throughout the UK. Just down the road from Holton is Minsmere, one of the largest sanctuaries for wild waterfowl in the country, and home to thousands of resident birds and resting place for migratory wild fowl from all over Europe and beyond.

In mobility and range, gulls could prove one of most effective and dangerous carriers and disseminators of the H5N1 virus. Breakdown of the gull population at Holton was black-headed gull (70%), herring gull (25%), the remainder mostly lesser black-backed gull (L. fuscus) and common gull (L. canus). DEFRA made repeated assurances about stepped up surveillance and said there was no evidence of H5N1 in wild birds.

When questioned by The Independent newspaper, a DEFRA official admitted that no tests were carried out on live wild birds within the restricted zone around Holton in the three weeks after the outbreak. The nearest sampling and testing of live wild birds took place 80km away at Welney in Norfolk. European virologists with long experience in testing wild birds for influenza type A viruses (which include those causing AI) have previously criticised sampling techniques used in the UK, and say this may be why such low rates of virus incidence (all sub-types) are traditionally recorded. This criticism, like the gull scenario at Holton, was never fully explained.

Free-range and intensively reared poultry at risk

Whether the source of the virus turns out to be the poultry trade or wild birds, the implications for continued health of the wild bird population are more worrying this time. Turkeys on the Bernard Matthews farm at Holton were intensively produced and continually housed. All poultry at Redgrave were free-range on a farm certified as organic by the regulatory body, the Soil Association. Redgrave Poultry (a subsidiary of Gressingham Foods) says every precaution was made to keep apart their poultry and wild waterfowl on the ornamental lake. Their birds were allowed outside access by day and housed at night. There were five paddocks for turkeys, one for geese and one for ducks. The birds did not have any access to the lake on the property because electrified and permanent fences, empty ground and a road segregated their poultry from the lake. Ducks, geese and turkeys were neither raised nor kept in the same paddocks.

It now appears that the H5N1 infection at Redgrave Park Farm now looks like an isolated outbreak but evidence shows it cannot be considered in isolation from recent H5N1 events elsewhere.

United Nations has claimed the virus may already be endemic in Eastern Europe, with ducks and geese as ‘silent carriers’ of H5N1. After months of denial, Hungarian authorities have admitted to the UK press that the H5N1 virus at Holton almost certainly originated in Hungary, which indicates that at least one outbreak in turkeys there was neither detected nor reported.

There is even speculation that the virus was brought into the UK by a migrant worker from Eastern Europe. Large numbers of Europeans from right across the new EU member states (including the Czech Republic and Hungary) are now working in UK agriculture.

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