In virus classification influenza viruses are RNA viruses that make up three of the five genera of the family Orthomyxoviridae:

	Influenzavirus A
	Influenzavirus B
	Influenzavirus C
	Influenzavirus D

 

These viruses are only distantly related to the human parainfluenza viruses, which are RNA viruses belonging to the paramyxovirus family that are a common cause of respiratory infections in children such as croup, but can also cause a disease similar to influenza in adults.

Figure 1. Noimanclature of influenza viruses