Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the transmission of an infectious pathogen, such as a foreign virus, between hosts belonging to different species. Once introduced into an individual of a new host species, the pathogen may  acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population. The concept is most commonly studied in virology, but cross-species transmission may also occur with bacterial pathogens or other types of microorganisms. Steps involved in the transfer of pathogens to new hosts include contact between the pathogen and the host , the successful infection of an initial individual host leading to amplification and an outbreak , and the generation within the original or new host of variants that have the ability to spread efficiently between individuals in populations of the new host. The phenomenon is important for understanding and controlling emerging infectious diseases in humans, especially those caused by viruses , where one reservoir species transfers the virus to a vector species, which in turn transfers the virus to humans . Most viral diseases of humans are zoonotic in origin, having been historically transmitted to human populations from various animal species; examples include SARS, Ebola, swine flu, rabies, and avian influenza. The exact mechanisms that facilitate cross-species transmission vary by pathogen, and even for widespread diseases are often unknown; however, it is believed that viruses with very high mutation rates are able to rapidly adapt to new hosts and thereby overcome host-specific immunological defenses, allowing their continued transmission. This may  occur between species which are frequently in  contact with each other. It can also occur  between species with low contact rates if facilitated by an intermediary species . For example, bats can directly transfer the rabies virus to humans through bites, and also through aerosolization of bat saliva and urine which can then be absorbed by human mucous membranes in the nose, mouth, and eyes. A host shifting event occurs when a strain that was previously zoonotic now circulates exclusively among humans. Similarity between host species  influences the likelihood that a pathogen can be transmitted between them  ; for example, most human zoonotic transmissions come from other species of mammals. This is believed to be facilitated by the similarity of the host species' immunological defenses. Pathogens of more distantly related species, on the other hand, such as plant viruses, are not known to infect humans . Other factors include geographic area, intraspecies behaviors, and phylogenetic relatedness .
Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the transmission of an infectious pathogen, such as a virus, between hosts belonging to different species. Once introduced into an individual of a new host species, the pathogen may cause disease for the new host and/or acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population. The phenomenon is most commonly studied in virology, but cross-species transmission may also occur with bacterial pathogens or other types of microorganisms. Steps involved in the transfer of pathogens to new hosts include contact between the pathogen and the host ; the successful infection of an initial individual host , which may lead to amplification and an outbreak ; and the adaptation of the pathogen, within either the original or new host , which may render it capable of spreading efficiently between individuals in populations of the new host. The concept is important in understanding and controlling emerging infectious diseases in humans, especially those caused by viruses . Most viral diseases of humans are zoonotic in origin, having been historically transmitted to human populations from various animal species; examples include SARS, Ebola, swine flu, rabies, and avian influenza. The exact mechanisms which facilitate cross-species transmission vary by pathogen, and even for common diseases are often poorly understood. It is believed that viruses with high mutation rates are able to rapidly adapt to new hosts and thereby overcome host-specific immunological defenses, allowing their continued transmission. A host shifting event occurs when a strain that was previously zoonotic begins to circulate exclusively among the new host species. Pathogen transfer is most likely to occur between species which are frequently in close contact with each other. It can also occur indirectly between species with less frequent contact if facilitated by an intermediary species ; for example, a reservoir species may transfer the virus to a vector species, which in turn transfers the virus to humans. The degree of phylogenetic relatedness between host species also influences the likelihood that a pathogen is transmitted between them , likely because of the similarity of the hosts' immunological defenses ; for example, most human zoonotic transmissions come from other species of mammals. Pathogens of more distantly related species, on the other hand, such as plant viruses, may not be capable of infecting humans at all . Other factors influencing transmission rates include geographic proximity and intraspecies behaviors .
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foreign
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cause disease for the new host and/or
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concept
phenomenon
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,
;
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leading
, which may lead
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, and the generation within
; and the adaptation of the pathogen, within either
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of variants that have the ability to spread
, which may render it capable of spreading
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phenomenon is important for
concept is important in
D
, where one reservoir species transfers the virus to a vector species, which in turn transfers the virus to humans
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that
which
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widespread
common
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unknown; however, it
poorly understood. It
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very
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This may
A host shifting event occurs when a strain that was previously zoonotic begins to circulate exclusively among the new host species.
A
Pathogen transfer is most likely to
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close
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indirectly
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low contact rates
less frequent contact
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. For example, bats can directly transfer the rabies virus to humans through bites, and also through aerosolization of bat saliva and urine which can then be absorbed by human mucous membranes in the nose, mouth, and eyes. A host shifting event occurs when a strain that was previously zoonotic now circulates exclusively among humans.
R
Similarity
; for example, a reservoir species may transfer the virus to a vector species, which in turn transfers the virus to humans. The degree of phylogenetic relatedness
A
also
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can be
is
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, likely because of the similarity of the hosts' immunological defenses
D
This is believed to be facilitated by the similarity of the host species' immunological defenses.
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are not known to infect humans
may not be capable of infecting humans at all
R
include geographic area, intraspecies behaviors, and phylogenetic relatedness
influencing transmission rates include geographic proximity and intraspecies behaviors