This transmission electron micrograph shows heaptitis B virus particles magnified one million times. In reality each particle is only 30 nanometers across, 20 times smaller than the wavelength of light. Viruses are very simple entities containing genetic material (coloured red here), within an outer protein coat (coloured blue-green here). Hepatitis B viruses are incredibly tough and diseases can be spread wherever needles are shared and sterilization practices are poor.