The H5N1 subtype of the influenza A causes the highly infectious "bird flu." The virus mainly infects birds, and outbreaks have resulted in mass culling within poulrty industries to prevent spread. In rare occasions, the virus can cross species and trasmit to humans, causing a severe, infectious flu with high mortality. Upon infection, the virus can spread quickly throughout the body, incubating within 2 to 17 days. H5N1 antibodies typically recognize antigens within the hemagglutinin (HA) and neuraminidase (NA) surface proteins.