Images Dated 12th September 2002

Ebola virus

Ebola virus. Coloured transmission electron micro- graph of a single Ebola virus, the cause of Ebola fever. It is one of the group of filoviruses, so- called for its thin and long shape. Here the viral filament is seen looping in on itself. A number of major outbreaks of this severe, frequently fatal viral haemorrhagic fever have occurred in equatorial Africa since 1976, one in Zaire in 1995. The virus appears similar to, but is antigenically distinct from the Marburg virus which causes green monkey disease. The illnesses from both Ebola and Marburg viruses are similar, with fever, skin rash, and haemorrhage. Death may be rapid. Magnification: x19, 000 at 6x7cm size. x66, 500 at 8x10". This is the "reston" strain of Ebola, from Philadelphia, USA

© Barry Dowsett/Science Photo Library

Natural freshwater pearls

Natural pearls from freshwater mussels. Pearls are accretions of nacre (calcium carbonate) secreted by certain oysters and mussels. The presence of a foreign body (such as a parasite or a grain of sand) within the shell triggers the secretion of nacre by the mollusc's mantle. Thin layers are deposited on the irritant particle and, over several years, a pearl is formed. Although commercially valuable pearls are obtained from freshwater mussels and oysters, the precious pearl comes from species of Margaritifera oysters found in tropical oceans. Cultured pearls are cultivated by inserting fragments of clam shell into the shells of farmed mussels and oysters

© VAUGHAN FLEMING/SCIENCE PHOTO LIBRARY