Systematic Veterinary Virology

MORPHOLOGY

• Influenza virus particles are highly pleiomorphic (variable). Mostly they appear as spherical/ovoid (80-120nm diameter). The outer surface of the particle consists of a lipid envelope. Hence these viruses are ether sensitive.
• Glycoprotein spikes project from these envelopes and these spikes are of two types haemagglutinin (HA) and neuraminidase (NA). The inner side of the envelope is lined by the matrix protein. The genome comprises of s/s (-) sense RNA in 8 segments.
• Each segment of RNA codes for one or two proteins. The fourth and sixth segment codes for haemagglutin (HA) and neuraminidase (NA) respectively. Variations observed in these two proteins are used to classify the virus specied into many strains (subtypes). There are 13 H and 9 N types. Common strains of SIV belong to H1N1, H3N2 and H1N2.