27 January 2012
Vol 335, Issue 6067

About The Cover

Cover image expansion

COVER False-colored transmission electron micrograph of a prion [average dimensions: ~150 nanometers (nm) long, 10 nm thick], the infectious protein responsible for deadly brain diseases in animals and humans. Although cross-species prion transmission may show no detectable sign of disease in the brain, lymphoid tissue is much more susceptible to infection. This discovery may be relevant when assessing the public health risks of exposure to animal prions and silent carriers of prion disease. See page 472. Image: Eye of Science/Photo Researchers, Inc.