Hepatitis B viruses, coloured transmission electron micrograph (TEM). They are a cause of liver inflammation. The smaller circles and the rod- shaped objects are surplus viral coat (capsid) protein from infected liver cells. These non- infectious antigens (foreign proteins) are used to make vaccines against hepatitis B. The complete viruses are called Dane particles. Hepatitis B is transmitted by infected blood, passed mainly through sexual intercourse or the sharing of needles by intravenous drug users. Symptoms include headache, fever, weakness and jaundice. Magnification unknown. Cover credit: DR LINDA STANNARD, UCT / SCIENCE PHOTO LIBRARY.