FLU-A H5

Influenza A is subclassified by its two major surface proteins: hemagglutinin, which mediates cell entry, first by recognizing host proteins bearing sialic acid on their surface, and second by triggering the fusion of viral and host membranes following endocytosis, allowing viral RNA to enter the cytoplasm; and neuraminidase, which cleaves sialic acid from host and viral proteins, facilitating cell exit12. There are 16 hemagglutinin subtypes (H1-16) and 9 neuraminidase subtypes (N1-9) that make up all known strains of influenza A viruses by various combinations of hemagglutinin and neuraminidase.