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跨物种病毒传播

根据美国微生物学会的文章称，病毒再次引起了一种新的疾病，并通过他们的主机切换能力引起轰动。非典型肺炎，埃博拉出血热和流感病毒已经是病毒从野生动物宿主中传播到人类宿主的例子。此外，据报道，当艾滋病毒跨越物种屏障，约70年前，通过灵长类动物感染了大量的人，成为一个延续至今的重大威胁。正如作者所述，在三个特定的阶段中，病毒性疾病出现，并成功地从供体主机切换到收体主机。因此，本文重点研究和探讨的变量，是新兴病毒性疾病在三个之前提到的阶段影响传染成功率的因素。这些变量的多样性影响主机切换机制，包括环境和人口壁垒,主机壁垒,现有的宿主范围,和病毒进化的传播,以及重组和病毒的中间体。

为了让主机切换成功,必须有病毒之间的相互作用和有潜在的新主机。但是,如果两者之间的接触是被预防或有限的,则会削弱了传播的可能性。这个障碍是可观测的,世界范围内前几次被转移给人类并没有成功,因为灵长类动物和人类之间的相互作用是有限的。然而,一旦灵长类动物能够接触到一个足够大的人群,传播变得成功，其影响仍然可以通过当今出现的感染看到。文章显示，病毒转移到人类宿主的种类很少，或根本不能传染，以及偶尔才出现能够产生和导致流行病的病毒。根据调查结果，各种人口因素和人类行为，如旅行，静脉吸毒，性行为和接触，农业的做法，农业扩张，都会增加病毒的主机切换，促进新的疾病的出现。正如作者所证实的，人类的贸易和旅游模式能够传播病毒和病毒的病原体，如非典型肺炎，而候鸟携带的流感病毒能够跨越广泛的人群。此外，马来西亚的尼帕病毒的出现正是人类活动造成的生态变化所带来的影响。例如，蝙蝠被认为是尼帕病毒库，当人们决定在养猪场种植果园，蝙蝠被果园吸引并感染猪。结果，与受感染的猪一起工作的人接触到病毒，这导致了动物病毒传播的增加。

Cross-Species Virus Transmission

According to the article supported by the American Society of Microbiology, viruses have once again been causing a stir in terms of giving rise to new diseases through their ability of host switching. SARS, Ebola fever and Influenza are a few examples in which viruses have underwent transmission from wildlife hosts onto human hosts. Furthermore, it was reported that when the HIV/AIDS virus crossed the species barrier from primate to human approximately 70 years ago, a major threat arose for a great amount of people were infected and still continue to be infected today. As outlined by the authors, there are three specific stages in which viral diseases emerge and successfully switch from donor host into recipient host. Therefore, this article focuses upon and examines the variables that affect the success rate of emerging viral diseases by the way they influence the three stages previously noted. The diversity of these variables which affect the mechanism of host switching consist of environmental and demographic barriers, host barriers, existing host ranges, and viral evolution in terms of transmission, recombination, reassortment and viral intermediates.

In order for host switching to be successful, there has to be interaction between the virus and the potential new hosts. However, if contact between the two is either prevented or limited, then the likelihood of transfer is weakened. This barrier is observable in the HIV virus, which prior to its global emergence was transferred to humans several times with little success because of the limited interaction between primates and human. However, once primates were able to come into contact with a large enough human population, transmission became successful and the effects can be viewed today for infections still arise. Figure 2 in the article shows the transfer of viruses into human host populations with little or no transmission along with the occasional viruses that are able to emerge and cause epidemics. Based upon findings, various demographic factors and human behaviors such as traveling, intravenous drug use, sexual practices and contacts, farming practices, and agricultural expansion increase viral host switching and promote the emergence of new diseases. As confirmed by the authors, human trade and travel patterns were able to spread insect vectors of viruses and viral pathogens such as SARS while migratory birds carrying the Influenza A virus were able to span across a wide range of populations. In addition, ecological changes brought upon by human actions have impacted the emergence of the Nipa