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Animal-borne diseases, or zoonoses, are any type of animal disease that can be transmitted to humans. These diseases may be caused by a variety of pathogens (e.g., viruses, bacteria, parasites, fungi) and can be present, but cause no symptoms in animals.

The plague, flu and tuberculosis are all well-known animal-borne diseases that have killed millions of people. They are caused by different pathogens, transmitted in different manners and cause different symptoms that can range from mild to deadly.

For most people, there is little risk of being infected by an animal-borne disease. This is despite the presence of cats and dogs in more than half of all households in the United States, and the possibility of contact with animals on farms, in petting zoos or in the wild. People who are at most at risk for contracting an animal-borne disease are patients with some form of immunosuppression. A weakened immune system can result from age, medical conditions (e.g., HIV/AIDS) or medical treatments (e.g., organ transplant, certain medications). For those who have an increased risk of contracting a zoonosis, certain types of animals (e.g., stray cats or dogs, reptiles, primates) are not recommended as pets.

Animal-borne diseases can be transmitted to humans through many routes. Bites or scratches can penetrate the skin and deposit pathogens. Inadvertent hand-to-mouth transmission can also occur after contact with an animal or their excretions. Following excretion, pathogens in dried can become airborne and be inhaled.

If any of these modes of transmission allows an infection to occur, a wide range of disease symptoms can follow. The symptoms experienced depend on the type of pathogen involved, the patient’s overall health, and the severity of the infection. Some infections may clear without medical treatment. If treatment is required, a physician will need to know about all animals with which a patient has had contact, the nature of the contact and when it occurred. In addition, blood tests and tissue samples may be necessary for a definitive diagnosis.

Many animal-borne diseases are treatable. Medications such as antibiotics, antivirals or antihelminthics may be prescribed. In addition, supportive treatments will help reduce the patient’s discomfort until the infection clears.