Zoonoses are defined as diseases and infections that are transmitted between vertebrate animals and humans. Currently there are more than 200 recognized zoonotic diseases, and 75% of emerging infectious diseases fit into this category. Zoonotic diseases can be transmitted to humans through bites and scratches, direct contact, aerosols, arthropod vectors, or contamination of food or water. There are many reasons for the increased impact of zoonotics in current times. Contact with domestic animals continues to be frequent, even in urban centers. Pets are a major reservoir and source of zoonoses, especially for children. In 2011–2012, 62% of US households, or approximately 72.9 million total households, owned a pet: 39% of households owned a dog, 33% owed a cat, 5% owned a pet bird, and 4% owned a reptile. The total number of animals owned was 78 million dogs, 86 million cats, 16 million birds, and 4.6 million reptiles. Other common pets include fish, rabbits, hamsters, gerbils, mice, and farm animals such as horses.
Recent factors that have had a substantial impact on emergence of zoonotics are human encroachment on wildlife habitat, wildlife trade and translocation, the ownership of exotic pets, petting zoos, and ecotourism. The epidemics of severe acute respiratory syndrome (SARS), West Nile virus, and monkeypox in North America have demonstrated the role of wildlife and exotic pets in the emergence of zoonotic diseases in industrialized nations. Traditional leisure pursuits such as hunting, camping, and hiking are increasingly common and continue to bring people into close contact with wild animals, arthropods, and sometimes contaminated water. Occupational exposures to domestic animals or animal products, especially in backyard operations, remain a leading cause of zoonotic disease exposure.