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Coloured transmission electron micrograph (TEM) showing monkeypox virus particles from a human skin sample. On the left, mature, oval shaped virus particles are seen. Immature virus particles (circular shaped, right) are also seen. Monkeypox particles are composed of a DNA (deoxyribonucleic acid) genome surrounded by a protein coat and lipid envelope. This virus, which is found near rainforests in Central and West Africa causes disease in humans and monkeys, although its natural hosts are rodents. It is capable of human to human transmission. In humans it causes fever, swollen glands and a rash of fluid-filled blisters. It is fatal in 10 per cent of cases. (KEYSTONE/SCIENCE PHOTO LIBRARY/CDC/SCIENCE PHOTO LIBRARY)