Any disease or infection that is naturally transmissible from vertebrate animals to humans and [no-glossary]vice-versa is classified as a zoonosis or zoonotic disease according to the Pan American Health Organization publication "Zoonoses and communicable diseases common to man and animals". According to the publication, over 200 zoonoses have been described and known for many centuries.
Acha PN, Szyfres B [Pan American Health Organization (PAHO)]. Zoonoses and communicable diseases common to man and animals. Volume 2. Chlamydioses, rickettsioses, and viroses. 3rd ed. Washington DC: PAHO; 2003. Scientific and Technical Publication No. 580. Eastern equine encephalitis; p. 110-115.
In recent years, zoonoses and communicable diseases common to man and animals have gained increasing attention worldwide. Human diseases that have their origins in infected animals, such as AIDS or Creutzfeldt-Jakob, have highlighted the need for a better understanding of animal diseases. The ease and speed of modern travel facilitates the spread of diseases once confined to specific geographic areas, as recently occurred with the widely publicized severe acute respiratory syndrome (SARS) epidemic. Animal migration and trade pose a similar threat, as was shown by the outbreaks in the United States of West Nile fever, and most recently, monkeypox—two diseases not previously known in the Western Hemisphere. Each of these examples highlights the need for accurate, up-to-date information, such as that presented in the latest edition of Zoonoses and Communicable Diseases Common to Man and Animals.