viruses are everywhere; they are found in all living species, including farm animals. However, as long as the animals are healthy, their defense systems (immune systems) keep them under control. About 10,000 years ago, humans learned to domesticate certain docile animal species, and to breed them for food and clothing. These farming practices worked reasonably well, except for the occasional outbreak of viral diseases such as foot and mouth disease, cattle plague (rinderpest), African swine fever, avian influenza, and salmon rhabdoviruses. However, since the advent of intensive industrial farming practices after World War Two, these and other animal virus diseases have become much more frequent, as a consequence of the stressful existence of the animals. In these conditions the animal defenses can no longer control the viruses, which then multiply and disseminate freely. Sophisticated gene sequencing techniques have shown recently that, each time one of these viruses multiply,...