A zoonotic disease (or zoonosis) is a disease or infection caused by bacteria, parasites, viruses or fungi that is transmitted between vertebrate animals and humans.

Transmission occurs through:

• direct contact (with the saliva, blood, urine or other body fluids of an infected animal)
• indirect contact (contact with contaminated air droplets, objects or surfaces or through contaminated food or water)
• bites of infected arthropod vectors (see also vector-borne diseases). 

Due to our close relationship with animals in agriculture, as companions and in the natural environment, zoonoses comprise a large proportion of existing and emerging diseases in humans around the world.

Examples of zoonotic diseases are cat scratch disease, brucellosis, hantavirus disease, rabies, leptospirosis, anthrax, tularaemia, psittacosis, Q fever, echinococcosis, avian and swine influenza, etc.