Cutaway model of an influenza virus particle showing internal structures. Superficially you can see the spikes of Haemagglutinin (red) and Neuraminidase (squarish and yellow). These spikes pass through the greenish viral envelope to dock with the underlying matrix (M) proteins shown in purple. Inside the matrix shell you can glimpse the dark yellow tubular ribonucleoproteins that house the viral genome. Flu viruses have eight of these RNPs. This allows different strains to easily form from existing types if more than one type of flu virus has infected the same cell at the same time. These illustrations are ideal for educators and public health campaigns. They are high resolution (5000 pixels across) and so are suitable for large poster displays.