Imported day-old ducklings from the Netherlands are now being investigated as a possible route for the H5N1 avian flu virus arriving in Britain.

The Times has learnt that Gressingham Foods received regular supplies of ducklings delivered by a Dutch exporter. The focus of inquiries is on the vehicle and driver, whether there are any links with previous outbreaks of the virus in mainland Europe and whether there was any opportunity for the disease to be spread through the Gressingham company via vehicles, equipment or staff.

The strain of virus in Suffolk is almost identical to one that infected ducks on a farm outside Munich in southern Germany in September. The same virus was also found in outbreaks in the Czech Republic in August. Ducks have shown no symptoms of disease in Suffolk but some can act as carriers without showing symptoms. Blood samples are being taken to see if they could have transmitted the virus to turkeys.

Imports of speciality poultry meats by Gressingham Foods are also part of the official inquiry. This meat is frequently processed or packed at the company’s plant less than 750 yards from Redgrave Park Farm, near Diss, which is at the centre of the alert. Gressingham regularly imports guinea fowl, poussin, barbary duck breasts and legs and smoked duck breasts.

An audit trail is being conducted to see whether any imported meat came from European farms near recent outbreaks of bird flu.

The virus can live in poultry faeces which can be transferred by vehicles, drivers, farm staff, bird crates, packaging, feathers or live birds. It can travel on footwear and on tyres. The virus in faeces can survive for several weeks, depending on conditions such as temperature and humidity.

A cull of 5,000 turkeys, 1,200 ducks and 500 geese is still under way at Redgrave Park Farm and a further 22,000 turkeys on four other farms in the area are to be slaughtered as “dangerous contacts”.

The four new premises are Stone House Farm in West Harling and Bridge Farm, Pulham, both in Norfolk, and Grove Farm, in Botesdale, and Hill Meadow, in Knettishall, both in Suffolk. No disease has been identified in these birds but there is concern about possible spread of the virus by five poultry workers who operated between these five premises, all run by Gressingham.

In East Anglia, 25 million turkeys are farmed. Many are for export but more than three million are destined for the £400 million domestic Christmas market. Many are breeding birds.

An air exclusion order has been made above the infected farms to prevent broadcast companies hiring helicopters to film the scene.

Fred Landeg, the acting chief veterinary officer, was concerned that helicopters would disturb the birds, delaying the cull, and could also spread the disease.

Britain’s emergency stockpile of flu drugs must be doubled or even tripled to give the country the best chance of containing a pandemic, the Government’s own scientific advisory panel has recommended.

The supply of 14.6 million doses of the antiviral drug Tamiflu, enough for a quarter of the population, is too small to ensure that the maximum number of lives would be saved, an official report has concluded.

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