In this article we will discuss about the structure of influenza viruses (explained with diagram).
Particles of influenza virus are highly pleomorphic, mostly spherical having 80-120 nm diameter. But it also occurs in other form like long filamentous particles (2,000 nm long, and 80-120 nm diameter). They have helical symmetry also.
The outer surface of the viral particle consists of a lipid envelope from which prominent two types of about 500 glycoprotein spikes are projected (each of which projects 10 to 14 nm from the surface): haemagglutinin (HA), and neuraminidase (N A) (Fig. 17.34 A-B).
The clusters of neuraminidase (NA) with a ratio of HA to NA to about 4-5:1, irregularly interpose the major glycoprotein (HA). The number of N spike per virion is about 100. The nucleocapsids are enclosed by lipoprotein membranes.
The inner side of the envelope is lined by two types of the matrix protein. Ml and M2 as well as non-structural (NS1 and NS2) proteins at some places. These proteins provided rigi framework to the virion and stabilize the lipoprotein envelope.
Influenza A viruses are further classified on the basis of viral surface proteins, hem-agglutinin (H) and neuraminidase (N). Sixteen H subtypes or serotypes and nine N subtypes of influenza A virus have been identified.
The spikes provide antigenic properties to the virus. Therefore, several antigens have been identified on the basis of difference in H and N antigens. The virus becomes ineffective after removing the spikes by treating with proteolytic enzymes.
