RNA strands specify the structure of proteins that are most medically relevant as targets for antiviral drugs and antibodies. HA and NA are also used as the basis for the naming of the different subtypes of influenza A viruses. This is where the H and N come from in H5N1. Influenza A viruses are significant for their potential for disease and death in humans and other animals. Influenza A virus subtypes that have been confirmed in humans, in order of the number of known human pandemic deaths that they have caused, include: H1N1, which caused the 1918 flu pandemic ("Spanish flu") and the 2009 flu pandemic ("swine flu") and is causing seasonal human flu H2N2, which caused "Asian flu" H3N2, which caused "Hong Kong flu" and causes seasonal human flu H5N1, ("bird flu"), which is noted for having a strain (Asian-lineage HPAI H5N1) that kills over half the humans it infects, infecting and killing species that were never known to suffer from influenza viruses before (e.g. cats), being unable to be stopped by culling all involved poultry—some think due to being endemic in wild birds, and causing billions of dollars to be spent in flu pandemic preparation and preventiveness H7N7, which has unusual zoonotic potential and killed one person H1N2, which is endemic in humans and pigs and causes seasonal human flu H9N2, which has infected three people H7N2, which has infected two people H7N3, which has infected two people H10N7, which has infected two people H7N9, which as of Feb 2014 has infected 309 people, and lead to 70 deaths Low pathogenic H5N1 Low pathogenic avian influenza H5N1 (LPAI H5N1) also called "North American" H5N1 commonly occurs in wild birds. In most cases, it causes minor sickness or no noticeable signs of disease in birds. It is not known to affect humans at all. The only concern about it is that it is possible for it to be transmitted to poultry and in poultry mutate into a highly pathogenic strain. 1966 – LPAI H5N1 A/Turkey/Ontario/6613/1966(H5N1) was detected in a flock of infected turkeys in Ontario, Canada 1975 – LPAI H5N1 was detected in a wild mallard duck and a wild blue goose in Wisconsin. 1981 and 1985 – LPAI H5N1 was detected in ducks by the University of Minnesota conducting a sampling procedure in which sentinel ducks were monitored in cages placed in the wild for a short period