Abstract
The viruses under the family Orthomyxoviridae are responsible for a variety of important respiratory diseases in humans and different animal species. The seven genera under the family are the influenza viruses A, B, C and D, Quaranjavirus, Thogotovirus and Isavirus. Viruses are highly evolving, and the genetic reassortment among viruses is seen only within the same genus and never been reported in between viruses from different genera. Influenza A viruses (IAVs) infect humans and different animals including birds, pigs, equines, dogs, cats, whales and seals. To date, there are 18 different haemagglutinins (H1 to H18) and 11 different neuraminidases (N1 to N9) for influenza A viruses. Influenza B viruses (IBVs) are exclusively human pathogens, while influenza C virus (IVC) affects humans and pigs. Serological evidence of ICV was recently detected in camels. Influenza D virus (IDV) was reported in pigs with influenza-like symptoms. IAVs cause recurrent epidemics of varying severity in humans and different animal species due to antigenic drift, gradual accumulation of point mutations, during replication under immune pressure induced by vaccines or prior infections. Several animal species act as important mixing vessel hosts. This chapter provides information on various orthomyxoviruses emphasizing upon virus properties, strains/types, genome, host, ecology, pathobiology, diagnosis and control.