H5N3 influenza A virus particles. Coloured transmission electron micrograph (TEM) of the H5N3 strain of influenza virus type A. All five H5 strains (H5N1,H5N2,H5N3,H5N8 and H5N9) cause bird flu. The virus consists of ribonucleic acid (RNA),surrounded by a nucleocapsid (yellow) and a lipid envelope (orange). In the envelope are two types of protein spike,haemagglutinin (H) and neuraminidase (N),which determine the strain of virus. This virus strain was responsible for the flu pandemic of 1968-1969,called Hong Kong flu,which infected an estimated 50 million people in the United States and killed 33,000 of these |