   zoonosis (; also spelled zoÃ¶nosis; plural zoonoses) is any process whereby an infectious disease is transmitted between different species of animals. often the term is used specifically to refer to diseases that originate in other species of animal, but that get transmitted to humans. zoonoses in which humans are infected may originate in either domestic animals or wildlife, such as insects, mammals, reptiles, or birds. in some zoonoses, humans infect other animals; this is sometimes called reverse zoonosis or anthroponosis ("anthropo-" being greek for "human"). in direct zoonosis the agent needs only one host for completion of its life cycle, without a significant change during transmission. many strains of influenza are common examples. "direct zoonosis" also may refer to transmission between hosts when one animal directly passes the disease to another. in contrast, in those terms indirect zoonosis is transmission via an intermediate host species that may carry the disease without showing ill effects itself. an animal that transmits a disease in such a way is are known as a vector. many serious epidemic diseases are zoonoses that originated in animals. these include rabies, ebola virus disease and influenza. in a systematic review of 1,415 pathogens known to infect humans, 61% were zoonotic. the emergence of a pathogen into a new host species is called disease invasion or disease emergence. the emerging interdisciplinary field of conservation medicine integrates human and veterinary medicine, and environmental sciences; conservation medicine is largely concerned with zoonoses. ==etymology== zoonosis is derived from the greek words Î¶á¿·Î¿Î½ zoon "animal" and Î½ÏÏÎ¿Ï nosos "ailment". ==historical development of zoonotic diseases==  during most of human prehistory groups of hunter-gatherers usually numbered fewer than 150 individuals. such groups seldom made contact with other bands. such isolation commonly caused epidemic diseases to burn out after their first run through a population, because epidemics depend on 
Animal_diseases Zoonoses