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Find information on animal health topics, written for the veterinary professional.

Introduction to Diseases Spread from Animals to People (Zoonoses)

By Stephen C. Waring, DVM, PhD, Assistant Professor, Epidemiology and Environmental Science;Associate Director of Research, Center for Biosecurity and Public Health Preparedness, School of Public Health, University of Texas Health Science Center;School of Public Health, University of Texas Health Science Center ; Donald Armstrong, MD, Emeritus Chief;Professor of Medicine, Infectious Disease Service, Memorial Sloan Kettering Cancer Center;Cornell University Medical College ; James H. Steele, DVM, MPH, Professor Emeritus, Center for Infectious Diseases, School of Public Health, University of Texas

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Diseases that are passed from animals to people (called zoonotic diseases or zoonoses) present an ongoing public health concern. Many organisms (such as bacteria and viruses) that infect animals can also cause disease in people. These organisms can be passed on in a number of ways. Contact with the animal itself is one way that disease is spread, but other ways include contact with urine, feces, or respiratory secretions of an infected animal, or contact with other items in the animal’s environment. Disease can also be spread through scratches or bites by a pet, or by insects that carry the infection from animals to humans.

Many known zoonotic diseases are passed from wild animals to people, or from wild animals to pets to people. Exposure to animals kept as pets is steadily increasing as the number of pets increases in the United States and other countries. The number of different types of animals kept as pets is also increasing. Exotic pets such as prairie dogs have become popular in many parts of the world. Such animals have brought diseases out of the wild and into human homes. For example, in 2003 an outbreak of monkeypox (a rare viral disease) occurred in people who were exposed to the virus by recently purchased prairie dogs. It was later determined that the prairie dogs likely were exposed to the virus when they came into contact with another exotic species, the Gambian rat, at a pet distributor.

In addition, exposure to wild animals is increasing as humans continue to clear land and build houses in areas that were formerly home to wildlife. Animals such as raccoons have adapted to urban conditions and are common carriers of rabies. People’s desire to touch wild animals and livestock has resulted in the establishment of petting zoos. Public health officials in several countries, including the US, Canada, and United Kingdom, are trying to control the spread of disease at these zoos through inspections and rules, including handwashing with antibacterial soap.

People with weakened immune systems, such as those with AIDS (acquired immune deficiency syndrome) are much more likely to get diseases from animals, including tuberculosis and foodborne Salmonella infections. Some very rare diseases may emerge in individuals who have AIDS or other conditions that impair the body’s ability to fight infections. Many of these organisms do not ordinarily cause disease.