Introduction to Diseases Spread between Animals and People (Zoonoses)

Diseases passed between animals and 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. People with compromised immune systems are at greater risk for zoonotic infections.

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 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.

Many viruses, such as coronaviruses, have the ability to quickly mutate and change their genetic code. These changes can sometimes enable them to infect a new species, including humans. The COVID-19 pandemic is believed to have resulted from a novel coronavirus, SARS-CoV2, “jumping” from wildlife to people. Ongoing surveillance of infectious disease at the interface of human and wildlife populations is critical for early zoonotic disease detection.