To the Editor: Bird flu or avian flu, caused by H5N1 virus, is a new emerging infectious disease. It is noted that this H5N1 virus jumped the species barrier and caused severe disease with high mortality in humans in many countries. The continued westward To the Editor: Bird flu or avian flu, caused by H5N1 virus, is a new emerging infectious disease. It is noted that this H5N1 virus jumped the species barrier and caused severe disease with high mortality in humans in many countries. The continued westward