Poultry farmers around Europe were on guard Monday against the possible spread of bird flu across the North Sea from infected Britain, fearing the disease could be carried by wild birds. The Netherlands was the first country over the weekend to order restrictions on commercial poultry since the outbreak last week on a turkey farm in eastern England of the H5N1 strain of the virus, which can be deadly for humans. Dutch farmers were told to keep their birds indoors or behind chicken wire and protective netting. "Double" disinfection procedures were imposed on shipments of birds and eggs to or from England. "The general picture is that farmers are obeying the rules," said Roel Vincken, spokesman for the Dutch Agricultural Inspection Service. The European Union's top health official urged veterinary authorities around the EU to step up vigilance, warning that further outbreaks were likely in the months ahead.