text: Swiss-Prot lists 137 types of neuraminidase from various species as of October 18, 2006. Nine subtypes of influenza neuraminidase are known; many occur only in various species of duck and chicken. Subtypes N1 and N2 have been positively linked to epidemics in humans, and strains with N3 or N7 subtypes have been identified in a number of isolated deaths.
  CAZy defines a total of 85 glycosyl hydrolase families, of which families GH34 (viral), GH33 (cellular organisms), GH58 (viral and bacterial), GH83 (viral) are major families that contain this enzyme. GH58 is the only endo-acting family.
  The following is a list of major classes of neuraminidase enzymes:
  * Viral neuraminidase
  * Bacterial neuraminidase
  * Mammalian neuraminidases: