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Zoonoses (, plural -, also spelled zoönoses; singular zoonosis (or zoönosis); from Greek: ζῷον ''zoon'' "animal" and νόσος ''nosos'' "ailment") are infectious diseases of animals (usually vertebrates), that can naturally be transmitted to humans.〔(【引用サイトリンク】title=Zoonoses )〕〔(【引用サイトリンク】title=Zoonosis )〕 Major modern diseases such as Ebola virus disease and influenza are zoonoses. Zoonoses can be caused by a range of disease pathogens such as viruses, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in animals; however, only diseases that routinely involve animal to human transmission, like rabies, are considered as zoonoses. Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from animals to humans through media such as air (influenza) or through bites and saliva (Rabies).〔(【引用サイトリンク】title=Zoonosis )〕 In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting infected. When humans infect other animals; it is called reverse zoonosis or anthroponosis. ==History== 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 constant contact with humans who have not developed an immune response. To persist in such a population, a pathogen either had to be a chronic infection, staying alive and infectious in the host for long periods, or it had to have a non-human reservoir in which it could survive until new hosts made contact. In fact, for many 'human' diseases, the human is actually an accidental or incidental victim and a dead-end host. Examples include rabies, anthrax, tularemia and West Nile virus. Thus, much of human exposure to infectious disease has been zoonotic. Many modern diseases, even epidemic diseases, started out as zoonotic diseases. It is hard to establish with certainty which diseases jumped from other animals to humans, but there is increasing evidence from DNA and RNA sequencing, that measles, smallpox, influenza, HIV, and diphtheria came to us this way. Various forms of the so-called "common cold" and tuberculosis also are adaptations of strains originating in other species. Zoonoses are of interest because they are often previously unrecognized diseases or have increased virulence in populations lacking immunity. The West Nile virus appeared in the United States in 1999 in the New York City area, and moved through the country in the summer of 2002, causing much distress. Bubonic plague is a zoonotic disease, as are salmonellosis, Rocky Mountain spotted fever, and Lyme disease. A major factor contributing to the appearance of new zoonotic pathogens in human populations is increased contact between humans and wildlife. This can be caused either by encroachment of human activity into wilderness areas or by movement of wild animals into areas of human activity. An example of this is the outbreak of Nipah virus in peninsular Malaysia in 1999, when intensive pig farming began on the habitat of infected fruit bats. Unidentified infection of the pigs amplified the force of infection, eventually transmitting the virus to farmers and causing 105 human deaths. Similarly, in recent times avian influenza and West Nile virus have spilled over into human populations probably due to interactions between the carrier host and domestic animals. Highly mobile animals such as bats and birds may present a greater risk of zoonotic transmission than other animals due to the ease with which they can move into areas of human habitation. Because they depend on the human host for part of their life-cycle, diseases such as African schistosomiasis, river blindness, and elephantiasis are ''not'' defined as zoonotic, even though they may depend on transmission by insects or other vectors. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「zoonosis」の詳細全文を読む スポンサード リンク
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