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Zoonosis (pronounced zoo-e-no-sis) is any infectious disease that may be transmitted from other animals, both wild and domestic, to humans or from humans to animals. The word is derived from the Greek words zoon (animal) (pronounced as zoo-on) and nosos (disease). Many serious diseases fall under this category. The plural of zoonosis is zoonoses, from which an alternative singular zoonose is derived by back-formation. The simplest definition of a zoonosis is a disease that can be transmitted from other animals to humans. A slightly more technical definition is a disease that normally exists in other animals, but also infects humans. The emerging interdisciplinary field of conservation medicine, which integrates human and veterinary medicine, and environmental sciences, is largely concerned with zoonoses.
Partial list of carriers A partial list of agents that can carry infectious organisms that may be zoonotic includes: List of infective agents Zoonoses can be listed according to the infective agent: Partial list of important zoonoses Some of the more important zoonoses are: Other zoonoses might be This list is by no means complete. The influenza virus is an interesting example: it continually recombines genes between strains found in humans, swine and ducks, producing new strains with changed characteristics, and occasionally, as in 1918, killing millions worldwide. Historical development of zoonotic diseases Most of human prehistory was spent as small bands of hunter-gatherers; these bands were rarely larger than 150 individuals, and were not in contact with other bands very often. Because of this, epidemic or pandemic diseases, which depend on a constant influx of humans who have not developed an immune response, tended to burn out after their first run through a population. To survive, a biological pathogen had to be a chronic infection, stay alive in the host for long periods of time, or have a non-human reservoir in which to live while waiting for new hosts to pass by. In fact, for many 'human' diseases, the human is actually an accidental victim and a dead-end host. (This is the case with rabies, anthrax, tularemia, West Nile virus, and many others). Thus much of human development has been in relation to zoonotic, not epidemic, diseases. Many modern diseases, even epidemic diseases, started out as zoonotic diseases. It is hard to be certain which diseases jumped from other animals to humans, but there is good evidence that measles, smallpox, influenza, and diphtheria came to us this way. HIV, the common cold, and tuberculosis may also have started in other species. In modern days, zoonoses are of practical 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. The plague is a zoonotic disease, as are salmonella, Rocky Mountain spotted fever, and Lyme disease. The major factor contributing to the appearance of new zoonotic pathogens in human populations is increased contact between humans and wildlife (Daszak et al., 2001). This can be caused either by encroachment of human activity into wilderness areas or by movement of wild animals into areas of human activity due to anthropologic or environmental disturbances. An example of this is the outbreak of Nipah virus in peninsular Malaysia in 1999, when intensive pig farming intruded into the natural habitat of fruit bats carrying the virus. Unidentified spillover events caused infection of the pig population which acted as an amplifier host, eventually transmitting the virus to farmers and resulting in 105 human deaths (Field et al., 2001). 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. Diseases like malaria, schistosomiasis, river blindness, and elephantiasis are not zoonotic, even though they may be transmitted by insects or use intermediate hosts vectors, because they depend on the human host for part of their life-cycle. | ||||||||
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