An article published in the medical journal The Lancet explains how the avian influenza virus H5N1 is distributed in the body and its pathogenesis. Previously it was thought that the virus only grew in the lungs, but researchers have shown that it not only grew in the respiratory system, but also in the stomach and intestine, the immune system and the central nervous system, being able to cross the placenta. Published data are now of great importance for conducting clinical, pathological and epidemiological research, and will affect public health and health personnel.