Avian flu has spread to humans before, most notably H1N1 and H5N1, so the new strain could pose a threat to public health, scientists warned. ???HIV/AIDS, SARS, West Nile, Nipah and influenza are all examples of emerging infectious diseases that originated in animals,??? said W. Ian Lipkin, director of the Center for Infection and Immunity at Columbia University. ???Any outbreak of disease in dome