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The Avian Influenza disease Virus (AIV) belongs to the species influenza virus type A, family Orthomyxoviridae, genus Alphainfluenzavirus based on the International Committee of Viral Taxonomy.
Figure 1. Structure of the Avian Influenza virus.
The AIV is characterized by being surrounded by a phospholipid membrane and having a spherical or filamentous shape with a size of approximately 80-120nm.
It contains a genome composed of 8 segments of linear single-stranded RNA with a 3-5’ sense (negative).
The RNA genome codes for 11 proteins, nine of which are structural (PB2, PB1, PB1-F2, PA, HA, NA, M1 and M2) and two non-structural (NS1 and NS2).
The segments are:
Segment one codes for the polymerase enzyme PB2;
Segment two codes for the polymerase enzyme PB1 or PB1-F2;
Segment three codes for the enzyme acid polymerase PA.
The fourth segment codes for the adhesion glycoprotein called hemoagglutinin (HA), which is involved in the binding of the virus to the cell, determines the degree of virulence, and is the antigen that allows the classification of influenza A viruses into 18 different HAs (16 HAs in birds and 2HAs in bats).
The fifth segment codes for the nucleoprotein (N) and is the antigen that allows classification of influenza viruses by genus into A, B, C and D.
Segment six codes for neuroaminidase (NA), which is a glycoprotein present on the surface of the virus that is involved in the release of viral particles from host cell receptors and is the antigen that allows the classification of influenza virus type A into 11 distinct NA (9 NA in birds and 2 NA in bats).
Segment seven codes for the matrix (M1 and M2).
Finally, segment eight codes for the nonstructural protein NS1 and NS2.
The AIVs found in the bird class can express on their surface one of the 16 HA and one of the 9 NA that can theoretically give rise to 144 viral subtypes. These two proteins have antigenic variations through two mechanisms:
The first is antigenic drift consisting of base mutations (substitution, insertion, deletion or reversal) due to the lack of correction of the RNA polymerase enzyme during viral genome synthesis.
The second is by recombination of its segmented genes when a cell is infected by two different subtypes. The latter mechanism allows the virus to acquire genomic segments from other species such as pig and human.
NATURAL HOST OF AIV
Cur...
