The story of how viruses that affect humans and the animals we depend on emerge—and what we have learned about them after centuries of veterinary science.

In 1896, bacteriologist Ernest Hankin studied the Ganges and discovered something he could not explain. Despite receiving the semi-cremated remains of thousands of corpses, the river did not spread cholera. There was something invisible in the water that killed bacteria. Twenty years later, Félix d'Herelle found it in the feces of soldiers recovering from dysentery and named it bacteriophage—"the bacteria-eater." They were viruses. D'Herelle dedicated his life to using them against infections, was nominated for the Nobel Prize eight times without ever receiving it, and his work was buried when antibiotics arrived. Today, they have returned. Perhaps the Ganges was right.

Human health, animal health, and environmental health form a single system.

When the general public discovered the meaning of words like zoonosis, strain, cytokine storm, or airborne transmission, Pedro Rubio had already been working with them for four decades. Emeritus Professor of Infectious Diseases at the Faculty of Veterinary Medicine in León, he has witnessed major animal epidemics from the front line, handled swine coronaviruses in the laboratory, and applied—on farms, not in headlines—the very same measures of quarantine, isolation, biocontainment, and vaccination that the covid-19 pandemic placed at the center of public debate long before. For veterinarians, none of that was new.

This book is the fruit of that experience. It explains what viruses are and how they cause disease, why new epidemics emerge, and what this has to do with livestock intensification, ecosystem loss, or the incessant movement of people and goods. It traces pandemics that devastated millions of animals—rinderpest, porcine reproductive and respiratory syndrome, African swine fever—that the public never came to know, even though they should have served as warnings. It explains the fascinating world of swine coronaviruses, in constant evolution, and the extraordinary relationship between bats and viruses: animals that have coexisted for millions of years with Ebola and Marburg without falling ill, and whose immunological secret science has yet to fully decipher. And it ends where few virology books reach: giant viruses, zombie viruses rescued from permafrost, and bacteriophages—viruses that kill bacteria and may become our next line of defense against antibiotic resistance.

PEDRO RUBIO NISTAL (Castrocontrigo, León, 1955) is Emeritus Professor of Infectious Diseases and Epidemiology at the Faculty of Veterinary Medicine, University of León. A veterinarian by training and calling, he began his professional career in livestock operations before moving into teaching and research, where he has developed his entire career over more than four decades. He earned his PhD with a thesis on coronavirus and rotavirus infections in swine, completed a postdoctoral stay at the Faculty of Veterinary Medicine in Ghent, and formed and led a research group of international prestige specializing in digestive infectious diseases of swine. He has supervised numerous doctoral theses, several of them on coronaviruses, published his work in national and international scientific journals, and carried out extensive outreach work at congresses, courses, and technical seminars. His activity combines academic research with collaboration with livestock, food industry, and pharmaceutical companies; he is a founding member of two spin-off companies at the University of León, holds a patent for a worldwide-unique vaccine against swine dysentery, and is a member of the European College of Porcine Health Management. He has directly experienced and closely followed for decades the evolution of many infectious diseases in animals—an experience that lies at the heart of this book.