A zoonosis is a disease that can be transmitted to a human being from another animal, as contrasted to diseases that are primarily human in nature and diseases to which humans are not susceptible (see diseases, animal). The term derives from the Greek words for "animal" and "disease."
More than 100 zoonoses have been identified. Other than being shared by humans and animals, they are as varied in nature, mode of transmission, and seriousness as are diseases in general. They include bacterial illnesses such as glanders, leptospirosis, lyme disease, relapsing fever, and tularemia; viral illnesses such as psittacosis, rabies, spongiform encephalopathy, and yellow fever; rickettsial diseases such as Q fever, Rocky Mountain spotted fever, and typhus; and parasite-transmitted diseases such as leishmaniasis, river blindness, toxoplasmosis, and trypanosomiasis, as well as infestations by parasites themselves, such as hookworms and tapeworms.
Perhaps the most famous zoonosis, historically, has been bubonic plague. Other serious diseases that continue to affect many areas of the world include anthrax, brucellosis, viral encephalitis, and cattle-derived tuberculosis.