Flu virus particles. Computer artwork of influenza (flu) A viruses (virion). The virus consists of a core of RNA (ribonucleic acid, red and purple, centre) genetic material surrounded by a protein coat. Embedded in the coat are the surface proteins haemagglutinin and neuraminidase. Both surface proteins are associated with the pathogenicity of a virus. Haemagglutinin binds to host cells, allowing the virus to enter them and replicate. Neuraminidase allows the new particles to exit the host after replication.