Introduction to Diseases Spread Between Animals and People (Zoonoses)

Diseases that can be passed between animals and people are called zoonotic diseases, or zoonoses. These diseases are always a public health concern. Many tiny organisms, like bacteria and viruses, that infect animals can also make people sick. Some zoonotic diseases are more serious than others.

Diseases caused by bacteria and viruses can spread in different ways. One way is by direct contact with an infected animal. Another is through contact with an infected animal’s urine, feces (droppings), or body fluids like saliva or mucus. People can also get sick from scratches or bites from pets, or from insects that carry disease. Sometimes, people can get sick by handling objects that have touched infected animals. People with weak immune systems are more likely to contract zoonotic infections.

Many zoonotic diseases spread from wild animals to people, either directly from these animals or through pets' contact with wild animals. As the number and variety of pets in homes increases, and as more people take their pets to public places, diseases are moving from wild animals into homes. For example, prairie dogs have become popular pets in many countries. In 2003, there was an outbreak of mpox (formerly monkeypox), a rare viral disease, in people in the United States with pet prairie dogs. It was later found that the prairie dogs likely caught mpox from another exotic animal, the Gambian rat, at a pet distributor in Africa.

More recently, a dangerous bird flu virus (highly pathogenic avian influenza) that spread throughout the world, killing poultry, has also infected some people, although the risk is low for people who don't have direct contact with infected birds.

As people continue to build homes and clear land in areas where wild animals live, contact with wild animals increases. Raccoons, for example, have adapted to living in cities and often carry rabies—a zoonotic viral infection that spreads through contact with infected saliva and that is fatal to both animals and people.

Petting zoos, where people can touch wild and farm animals, have also grown in popularity. Public health officials in the United States, Canada, the UK, and other countries work to control the spread of disease at these zoos through inspections and enforcement of handwashing with antibacterial soap.

Many viruses, including coronaviruses, can change quickly by mutating (changing their genetic content). These changes sometimes allow viruses to infect new species, including people. The COVID-19 pandemic is believed to have started when a new coronavirus, called SARS-CoV-2, jumped from wildlife to people. Watching for new infectious diseases where people and wildlife interact is essential for detecting zoonotic diseases early.