In the early 1800s, animal owners and local healers provided most veterinary care, and indigenous healing methods thrived around the world. Colonialism, global trade networks, and other circulations of animals led to disease outbreaks (epizootics). Rinderpest, imported by Europeans, destroyed about 90 percent of all wild and domesticated bovines in sub-Saharan Africa, causing devastating famines. European-model veterinary schools continued to spread around the world. Their graduates worked to reduce competition by developing laws and regulations that forbade non-graduates from practicing animal healing. Veterinary leaders envisioned "scientific" veterinary medicine, using microscopes and other tools. By working to establish microbiology, comparative pathology, and "one medicine," veterinarians were important co-creators of modern medicine and public health as we know them today. Ideas about disease causation included the roles of the environment and insects in spreading disease; the contagium vivum; parasitism; toxins; and several germ theories. Some veterinarians treated companion (pet) animals, whose owners valued them for emotional reasons. Associations for the humane treatment of dogs and other animals were established. Pet owners increasingly expected scientifically trained veterinarians to provide the same services for pets that their owner could expect at a hospital for humans.