A Review of Strategic Immune Evasion by Influenza Virus and Antiviral Response of Interferon

Influenza virus belongs to the family orthomyxovirida. It is a major pathogen that has wide host range including humans, horses, pigs, mink, marine mammals, felids and a diverse range of domestic birds but shorebirds and wildfowl are considered to be the reservoir host in nature [1]. The influenza virus has an enveloped, segmented genome comprised of eight segments of negative sense-single stranded RNA (-ssRNA). The –ssRNA has coding ability of 11 proteins as Matrix proteins (M1 and M2), Hemagglutinin (HA), Neuraminidase (NA), Nucleocapsid Protein (NP), Polymerase basic protein (PB1, PB2, and PA), PB1-F2 and non-structural proteins (NS1 and NS2) [2]. Based on the surface glycoproteins the Hemagglutinin (HA) and Neuraminidase (NA), influenza viruses are classified into three types A, B and C. Viral entry in the host cell is mediated by receptor binding and membrane fusion activity of HA while NA mediates the release of viral progeny by enzymatic cleavage. The Influenza viruses that represent 16HA and 9NA antigenic subtypes have been identified in poultry and wild birds throughout the world. These antigenic subtypes can be found in different arrangements as H1N1, H16N3 [3]. Hemagglutinins are initially synthesized as a single polypeptide precursor (HA0), later these are cleaved into HA1 and HA2 subunits by proteases. The introduction of influenza virus subtypes H5 and H7 into the poultry is reported to be highly infectious and may cause outbursts of highly pathogenic avian influenza (HPAI, earlier known as B fowl plague) but this is not associated with other HA subtypes [4]. The introduction of basic amino acid residues into the cleavage site of HA0 converts the low pathogenic avian influenza virus to high pathogenic avian influenza virus, this HA0 helps in systemic replication of the virus [5]. The highly pathogenic influenza virus is responsible for the outbursts, as recurrent outbursts were recorded by influenza viruses of subtype H5N1 in Europe, the Middle East, Asia and Africa; H5N2 in Italy, Mexico and Texas; H7N1 in Italy; H7N3 Abstract