A huge range of diseases are caused by viruses, affecting every type of living thing from tiny bacteria to humans. But viruses can't live on their own. They spread by infecting living cells, hijacking their host's biological machinery to make new virus particles that burst out of the cell and transmit the infection. However, although thousands of viruses can start an infection in a cell, only a handful of them get passed on. And this means that the most infectious viruses are quickly separated out, spreading from one cell to the next without mixing – like these tomato plant cells infected with viruses labelled with different fluorescent colours. Although the cells in the middle – where the infection started – are a mixture of green and pink, the viruses quickly separate out as the infection spreads outwards. This 'self sorting' process helps to explain why viruses are so effective at spreading.
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.
BPoD is also available in Catalan at www.bpod.cat with translations by the University of Valencia.