The name originates from the Greek word “ortho” which means correct while “myxo” stand for mucus . The word essentially stands for virus that infects epithelial cells in the right way, exactly opposite to that of paramyxoviruses. The family Orthomyxoviridae contains viruses of single stranded segmented RNA genome (6-8 segments). Out of all, influenza viruses are the most important members of this family which includes influenza virus A, B, and C. The name originates during 18 th century from a disease that was thought to “ influence” by stars. The pathogenic viruses are included in the genus influenza virus A, whereas other two genera (B and C) circulate constantly in human subjects. Several devastating pandemics caused because of influenza virus in past include famous Spanish Flu (1918), Asian Flu (1956), and Hong Kong Flu (1967) which killed millions of people.

 

25.1 Distinct Characters

• I. The viruses cause an acute respiratory disease with prominent systemic symptoms with its major manifestation on the respiratory system.

II. Influenza virus type A is responsible for periodic epidemics worldwide; while virus types A and B cause regional epidemics during the cold weather.

III. Antigenic drift (minor changes in the viral surface proteins) and Antigenic Shift (major changes in the viral genome due to rearrangement of the virus segments or reassortments) are responsible for both epidemics and pandemics of influenza viruses.