A Canadian program aiming to discover any traces of the bird flu virus that may have arrived in the country via migratory birds is under way but has so far found no reason for concern. A quarter of the planned 12,000 birds have been tested to date, but no avian influenza viruses have been isolated, as one high ranking official of the Canadian Co-operative Wildlife Health centre declared in an interview. A similar nationwide program in the United States has also failed to spot any highly pathogenic flu virus and this is giving the experts a hint that migratory birds might be an unlikely way of the disease entering North America. Although some avian flu viruses are traced on birds, none is of the H5 or H7 subtypes, the ones causing high mortality among birds and. Mild, low pathogenic forms have been found in birds for years, but without any reason for concern for the public. This conclusion is soon to be published in an article by two scientists, that have analyzed the possibilities of the disease being introduced into the country. Their opinion is that diseased birds imported either legally or illegally are the most likely source of infection for North American poultry, more likely than migratory birds or birds from Asia or Africa blown off course by storms.