Post Reply - H7 flu

Hemagglutinin is a Class I Fusion Protein, having multifunctional activity as both an attachment factor and membrane fusion protein. Therefore, HA is responsible for binding Influenza virus to sialic acid on the surface of target cells, such as cells in the upper respiratory tract or erythrocytes,^[1] causing as a result the internalization of the virus.^[2] Secondarily, HA is responsible for the fusion of the viral envelope with the late endosomal membrane once exposed to low pH (5.0-5.5).^[3]

The name "hemagglutinin" comes from the protein's ability to cause red blood cells (erythrocytes) to clump together ("agglutinate") in vitro.^[4]

Viral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the virus to be released from the host cell. Neuraminidases are enzymes that cleave sialic acid (also called neuraminic acid) groups from glycoproteins. Viral neuraminidase was discovered by Alfred Gottschalk at the Walter and Eliza Hall Institute in 1957.^[3] Neuraminidase inhibitors are antiviral agents that inhibit influenza viral neuraminidase activity and are of major importance in the control of influenza.^[4]

Viral neuraminidases are the members of the glycoside hydrolase family 34 CAZY GH_34 which comprises enzymes with only one known activity; sialidase or neuraminidase EC 3.2.1.18. Neuraminidases cleave the terminal sialic acid residues from carbohydrate chains in glycoproteins. Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins.^{[citation needed]}

To infect a host cell, the influenza virus attaches to the exterior cell surface using hemagglutinin, a molecule found on the surface of the virus that binds to sialic acid groups.

Avian Influenza A(H7) Viruses

There are nine known subtypes of A(H7) viruses A(H7N1), A(H7N2), A(H7N3), A(H7N4), A(H7N5), A(H7N6), A(H7N7), A(H7N8), and A(H7N9)]. Most A(H7) viruses identified worldwide in wild birds and poultry are LPAI viruses. 

Avian influenza A(H7) virus infection of humans have occurred sporadically. 

The most frequently identified A(H7) viruses associated with human infections are avian influenza A(H7N9) viruses, which were first detected in China in 2013. While human infections with A(H7N9) viruses are uncommon, they have resulted in severe respiratory illness and death in approximately 40% of reported cases. In addition to A(H7N9) viruses, human infections with A(H7N2), A(H7N3), A(H7N4), and A(H7N7) viruses have been reported and have primarily caused mild to moderate illness with symptoms that included conjunctivitis and/or upper respiratory tract symptoms.