Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae. Influenza B virus is only known to infect humans and seals with influenza.Encyclopedia Entry for Influenza B :Influenza B virus. Influenzavirus B. Human,Respiratory, Associated with FluEncyclopedia Entry for Influenza B :Influenza B virus. Influenzavirus B. Human,Respiratory, Associated with Flu