Speaking at a press conference, Salgado said that no-one in Spain had been infected with the H5N1 virus and the appearance of one infected bird -- a great crested grebe found last Friday in the northern city of Vitoria -- did not mean there had been a mutation which could trigger a human pandemic.

Salgado stressed however, as bird flu in Spain was spreading within expected limits, the public had better become accustomed to the idea that an infected bird could appear from time to time, and that they should maintain sensible levels of vigilance.

Salgado said that the bird had been infected with a strain of H5N1 bird flu which was very similar to that seen in dead birds found elsewhere in Europe -- the Czech Republic, Greece, Germany and France.

The grebe, a bird that sometimes lives in woodland and wetlands, appeared to have been infected by a woodland bird, she said.

Spain, like other European nations, has not yet experienced bird flu infections among captive birds and there has not been any flu detected in commercial poultry farms, either in Spain or the surrounding nations.

Also on Wednesday, the country's Veterinary Alert Committee told the press it would increase its vigilance in the country's northern wetlands and the Ebro Valley. The team will increase its visits to wetland areas, with particularly thorough checks over the next 10 to 15 days: the time it takes for bird flu to incubate.

The Committee also agreed to extend the quarantine period and tighten related measures concerning birds kept close to wetlands, starting from Sept. 1 -- the day when the great north-south bird migrations over Spain begin.

Bird flu has infected 229 people and killed at least 131 people worldwide since it started late 2003 in Asia, according to the World Health Organization. Most of those who died worked closely with birds. Scientists fear that the virus could one day mutate into a version that could spread quickly between people.