Migratory birds may carry the deadly H5N1 avian flu virus to US northern states next summer, although samples taken from waterfowl in this year have shown negative results, scientists reported on Friday.

Scientists at the University of Alaska, Fairbanks, formed the Avian Influenza Program to study the evolution and assess the prevalence of the avian influenza viruses in Alaska, firstly the highly pathogenic H5N1 strain, in migratory birds.

Of the roughly 4,500 samples collected in this summer, 290 have been screened to determine the presence of any of the known subtypes of avian flu virus.

None of the viral isolation and subtyping to date has detected H5N1, although 30 of the 290 samples tested positive for other bird flu virus strains, the researchers said.

But next year the news may not be so good, they noted in a statement. They also urged the government to tighten the monitor network on wild migratory birds before the virus enters the United States.

"With a virus like H5N1 emerging in an area like Southeast Asiaand spreading toward Europe if it doesn't reach Alaska this year, those birds that go back may very well pick it up and bring it to Alaska next year to an environment where that H5N1 might mix with other strains it hasn't seen before," said Jonathan Runstadler, leading scientist of the project.

Alaska, at the overlap for parts of the Asian and North American flyways for migratory birds, could be the first stop when the killer avian flu spreads into the United States, scientists said.

The birds may carry the H5N1 virus to Alaska in summer when they fly back from Siberia, where they may have been infected with the H5N1 virus after close contact with local waterfowl, Runstadler said.

The environment of Alaska also provides an opportunity for exchange of different bird flu virus strains, which then may lead to new virus strains that are capable of infecting humans. Scientists said it is only a question of time that a flu pandemic aroused by such new strains kill millions of people.

The 1918 Spanish Influenza virus, which caused one of history'smost deadly epidemics, killed at least 50 million people around the world. Earlier this month, the virus was identified as a bird flu that jumped to humans.

According to US National Institutes of Health, the highly pathogenic H5N1 virus strain, currently circulating in Asia and part of Europe, has acquired five of the 10 gene sequence changes associated with the human-to-human transmission of the 1918 Spanish virus.

By now the H5N1 virus have sporadically infected pigs, cats, and humans. About 70 people in Southeast Asia were confirmed to beinfected with the H5N1 virus, and more than half died in this year' s outbreak.