Bacteria are unicellular entities that rank among the tiniest of all living organisms; viruses are biological entities that are even smaller than the smallest bacterial cell. But both can infect humans, other animals and vegetal organisms, causing serious and even lethal disease. From malaria to contemporary plagues (such as AIDS, or other sicknesses exaggerated by the media, like SARS or avian flu), the author tells the story of how these micro-organisms were discovered, describes their importance in human pathology, explains the mechanisms underlying their pathogenic action and identifies which tools help prevent and control infection.

Michele La Placa is professor emeritus of Microbiology at the University of Bologna and one of the pioneers of virological research in Italy.