Pathogen Gallery

Avian flu virus

Avian flu virus, computer artwork. A virus is a tiny pathogenic particle comprising genetic material enclosed in a protein coat. The coat contains surface proteins (spikes). Flu viruses have two types of surface protein, called haemagglutinin (H) and neuraminidase (N). These exist in several subtypes, only some of which are pathogenic in humans. The current bird flu that is endemic in birds is H5N1. The surface proteins are essential for the life cycle of the virus. Haemagglutinin allows the virus to bind to and enter a host cell, where the virus uses the cell's machinery to create more copies of the virus. Neuraminidase allows the new virus particles to exit the cell, so that they can infect others

© PASIEKA/SCIENCE PHOTO LIBRARY

Herpes virus replicating

Herpes virus replicating, computer artwork.Viruses are only able to replicate in a host cell.The glycoprotein spikes in the virus envelope(green) enable it to fuse with the host cell'smembrane (upper right). The virus capsid (proteincoat, blue), which contains its DNA(deoxyribonucleic acid) genome (red), is releasedinto the cell's cytoplasm. The virus particletravels to the nucleus (pink), entering it througha nuclear pore, and uses the cell's machinery toreplicate its own DNA and produce and assemble newcapsid proteins. The daughter DNA enters the newcapsids and the particles leave the nucleus, againthrough a nuclear pore. Envelope proteins areadded to the capsid by Golgi bodies in thecytoplasm. The viruses then leave the cell, readyto infect another cell

© Russell Kightley/Science Photo Library

E. coli bacterium, TEM

E. coli bacterium. Coloured transmission electron micrograph (TEM) of an Escherichia coli bacterium in the early stages of binary fission, the process by which the bacterium divides. This Gram-negative bacillus (rod-shaped) bacterium normally inhabits the human intestines. Under certain conditions it may undergo rapid division, which increases its numbers to such an extent that it causes infection. E. coli cause 80% of all urinary tract infections, travellers diarrhoea and gastroenteritis in children. The hair-like appendages around the bacterium are pili, structures used for bacterial conjugation. Magnification: x25, 000 when printed at 10cm wide

© CNRI/SCIENCE PHOTO LIBRARY