Viral diseases in animals

Animal diseases can be caused by viruses, which are self-reproducing agents that multiply only within susceptible living cells and lead to a wide range of infections and to cancer. The four main categories of viruses: animal and human; insect; plant; and bacterial, may be interchangeable and transmissible. For viruses to survive, there must be a means by which virus units can reach susceptible cells, multiply within these cells, and liberate into the environment. Viral animal diseases include rinderpest, rabies, distemper, hog cholera, fowl pox, infectious laryngotracheitis, Newcastle disease, and some cancers.