|Influenza virus particle, animation. The virus particle consists of coils of RNA (ribonucleic acid) genetic material surrounded by a nucleocapsid and a lipid envelope. The external structure consists of two types of protein embedded in the lipid envelope. These surface proteins are haemagglutinin (H, rounded) and neuraminidase (N, spike). These surface proteins are used for recognising and binding to the host cell. The proportion of H and N proteins determine the strain of influenza virus and the severity of an infection.