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建立人际资源圈Cross-Species Virus Transmission---Essay代写范文
2016-08-09 来源: 51Due教员组 类别: Essay范文
Essay代写范文：Cross-Species Virus Transmission这篇Essay范文讲述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。通过这篇科学杂志上的阅读，文章的主要目的是向读者介绍病毒是如何能够跨物种和带来新的传染病的信息。就从病毒宿主转换的可能性防止未来的流行病。
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 Nipah virus in Malaysia. For example, bats are considered to be the reservoirs of the Nipah virus, and thus when people decided to plant fruit orchards around piggeries, the bats became attracted to the orchards and caused a spillover which infected the pigs. In turn, people working with the infected pigs became exposed to the virus and this caused an increase in animal virus transmission.
Host barriers are the second variable examined in the article and proven to affect the mechanism of host switching. In order for transmission to be a possibility, a virus has to be able to infect cells of a new host. Yet, this process can be delayed at various levels such as receptor binding, entry into the cell, genome replication or gene expression. Based on these multiple host barriers, the virus would have to undergo changes to be able to overcome everything thus increasing the difficulty of transmission. Also this article states that innate antiviral responses from host cells and apolipoprotein B-editing catalytic polypeptide proteins (APOBEC) further impede the risk of infection by blocking infection to subsequent cells. In examining evolutionary relatedness, species that are closely related to one another have an increased likelihood of viral host switching as viewed between chimpanzees and humans, thus resulting in the establishment of HIV. On the other hand, due to relatedness, certain limitations based on cross-immunity to related pathogens and innate immune resistances to related viral groups arise. Another aspect to host barriers is the physical entry of the virus into the cell. Upon entry there are host glycans or lectins which bind to the virus particles to prevent infection. Also, lack of neuraminidase proteins, used in the process of egress, cause viral inactivation which further aids in the prevention of transmission and emergence. Because viruses are specific to their appropriate host, they are also specific to the various receptors in which they bind to the host cell. For example, the HIV virus binds specifically to CD4 host receptors whereas avian viruses recognize sialic acids found on host cells. Aside from receptor binding, there are also intracellular restrictions which decrease viral transmission. For example, interferon responses are found to be host specific and thus more likely to protect cells against viruses. This can be observed by alpha and beta interferons which restrict the murine norovirus from entering the host cell.
The author further examined the host ranges of viruses and whether or not they were a factor in host switching. It was conjectured that preexisting host ranges influence the ability of a virus to be established in a new host. Viruses were classified as either generalist, infecting many different hosts, or specialist, infecting only a few related hosts. The expectation was that generalist viruses would show a greater likelihood of shifting to additional hosts whereas specialist viruses would be more inclined to restrictions of host switching. However, looking at the data in Table 1, it became apparent that both generalist and specialist viruses have transmitted successfully into new hosts thus diminishing the overall generalization previously made.
The last variable under review for affecting the mechanism of host switching is the viral evolutionary mechanisms which consist of viral fitness trade-offs, modes of virus transmission, recombination and reassortment and viral intermediates. It has been speculated in the article that cross-species transmission is more common in rapidly evolving viruses. This means the greater the rate of variation, the more likely a virus is able to adapt to a new host and undergo transmission. Because RNA viruses lack proofreading mechanisms and contain large viral populations, they are more likely to undergo evolution and transmit within a new host. Yet, there is evidence that some RNA viruses have developed host specialization and that rates of variation of DNA viruses should not be underestimated in comparison to RNA viruses. Because viruses are able to undergo various mutations, this increases their ability to infect new hosts but in the long run reduces their fitness in the donor host. By observing Figures 2 and 3 in the article, this is deemed fitness trade-off. However, not all mutations cause a reduction in fitness trade-off for there are a few advantageous ones that increase fitness. Also, when only a few adaptive mutations are required between donor host and recipient host, transmission becomes more efficient. As far as emergence and successful host transfer are concerned, the modes of virus transmission cause limitations. For example, if viruses are not able to survive between donor, recipient and or vector hosts, then emergence becomes a challenge. Furthermore, different pathways of transmission either by droplet spread, sexual inoculation and or fecal-oral represent challenges in accommodating various hosts. Recombination and reassortment make viruses more susceptible to genetic changes that are beneficial in the long run. In comparing RNA and DNA viruses, the possibility of recombination varies but in observing the retrovirus HIV, there is a high rate of recombination which may correlate to its effective emergence. Figure 5 examines possible roles of recombination in the HIV virus as well as its origin from other primates. Another example of a recombination virus can be viewed in SARS CoV which most likely arose from a combination of a CoV virus and another bat virus before infecting human hosts. Once a virus has been able to switch to a new host, it further uses recombination and reassortment in the process of adaptation. Lastly, there have been cases in which viral intermediates with lower fitness were required in the process of successful transmission. Aside from viruses adapting to their new hosts they also have to optimize their intensity in the host cells at the same time evading any immune responses. By being able to detect viruses that do not spread efficiently, there would be a greater chance of controlling epidemic outbreaks.
Reading through this scientific journal, the main purpose of the article is to present the audience with information on how viruses are able to cross species and bring about new epidemic diseases. The authors mostly define the barriers that a virus has to overcome in order to obtain successful transmission and overall emergence by organizing the information into various subheadings. For example, in the section Environmental and Demographic Barriers to Host Switching, the authors compare human actions such as travel or trade and link these to viral host switching and the potential for infection. In the next section, they focus on the host and the barriers that the virus has to overcome in order to give rise to efficient transmission. Basically the virus has to be able to enter into potential host cellsand in doing so has to bind to receptors and then either fuse or undergo endocytosis. However, host cells have various mechanisms by which they are able to stop a virus from spreading and causing further infections. Next, there is a discussion about the relationship between the host range of a virus and whether or not it is a factor in determining the likelihood of host switching. The authors state that regardless of the host range of a virus, both generalist and specialist viruses have been successful in transmission into a new host. Lastly, the authors examine mutations and adaptations of viruses in response to their ability to emerge and cause diseases. These last few paragraphs consider what occurs once a virus has entered into a host cell and its ability to maintain entry by undergoing advantageous mutations or further adapting to the recipient hosts. The article ends with a basic summary or overview of all the information presented earlier with the outlook of being able to control future epidemic diseases. Upon reading this journal article, the style of writing is rather complex in certain sections which would inhibit the audience from fully understanding the material. Also, there appear to be no major experiments or tests conducted by the authors for the journal article only contains basic information and referenced data. Further, in quite a few sections, the authors use phrases such as, “poorly understood” and “we know relatively little” in discussing the information. This would most likely make the audience skeptical as to the authors' competence and understanding of the information being presented. In addition, while presenting their information, the authors mainly focus on few specific viruses such as HIV, SARS and Influenza. What about the rest? Are other viruses less prone to host switching or crossing barriers? These aspects need to be addressed so that the audience is not able to ponder and make generalizations. Lastly, no solution is stated as to the prevention of future epidemics from the possibility of viral host switching. The only statements made in the journal consisted of being able to better understand the information presented and the complexities that follow this topic. Overall, this article should only be used as background information in aiding previous knowledge on the topic. The authors accomplish the task of providing the audience with information, but the style and the presentation should have been executed differently.
51Due原创版权郑重声明：原创范文源自编辑创作，未经官方许可，网站谢绝转载。对于侵权行为，未经同意的情况下，51Due有权追究法律责任。
51due为留学生提供最好的作业代写服务，想获取更多Essay代写范文，亲们可以进入主页 www.51due.com 为留学生提供essay辅导服务，了解详情可以咨询我们的客服QQ:800020041哟。-lc
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 Nipah virus in Malaysia. For example, bats are considered to be the reservoirs of the Nipah virus, and thus when people decided to plant fruit orchards around piggeries, the bats became attracted to the orchards and caused a spillover which infected the pigs. In turn, people working with the infected pigs became exposed to the virus and this caused an increase in animal virus transmission.
Host barriers are the second variable examined in the article and proven to affect the mechanism of host switching. In order for transmission to be a possibility, a virus has to be able to infect cells of a new host. Yet, this process can be delayed at various levels such as receptor binding, entry into the cell, genome replication or gene expression. Based on these multiple host barriers, the virus would have to undergo changes to be able to overcome everything thus increasing the difficulty of transmission. Also this article states that innate antiviral responses from host cells and apolipoprotein B-editing catalytic polypeptide proteins (APOBEC) further impede the risk of infection by blocking infection to subsequent cells. In examining evolutionary relatedness, species that are closely related to one another have an increased likelihood of viral host switching as viewed between chimpanzees and humans, thus resulting in the establishment of HIV. On the other hand, due to relatedness, certain limitations based on cross-immunity to related pathogens and innate immune resistances to related viral groups arise. Another aspect to host barriers is the physical entry of the virus into the cell. Upon entry there are host glycans or lectins which bind to the virus particles to prevent infection. Also, lack of neuraminidase proteins, used in the process of egress, cause viral inactivation which further aids in the prevention of transmission and emergence. Because viruses are specific to their appropriate host, they are also specific to the various receptors in which they bind to the host cell. For example, the HIV virus binds specifically to CD4 host receptors whereas avian viruses recognize sialic acids found on host cells. Aside from receptor binding, there are also intracellular restrictions which decrease viral transmission. For example, interferon responses are found to be host specific and thus more likely to protect cells against viruses. This can be observed by alpha and beta interferons which restrict the murine norovirus from entering the host cell.
The author further examined the host ranges of viruses and whether or not they were a factor in host switching. It was conjectured that preexisting host ranges influence the ability of a virus to be established in a new host. Viruses were classified as either generalist, infecting many different hosts, or specialist, infecting only a few related hosts. The expectation was that generalist viruses would show a greater likelihood of shifting to additional hosts whereas specialist viruses would be more inclined to restrictions of host switching. However, looking at the data in Table 1, it became apparent that both generalist and specialist viruses have transmitted successfully into new hosts thus diminishing the overall generalization previously made.
The last variable under review for affecting the mechanism of host switching is the viral evolutionary mechanisms which consist of viral fitness trade-offs, modes of virus transmission, recombination and reassortment and viral intermediates. It has been speculated in the article that cross-species transmission is more common in rapidly evolving viruses. This means the greater the rate of variation, the more likely a virus is able to adapt to a new host and undergo transmission. Because RNA viruses lack proofreading mechanisms and contain large viral populations, they are more likely to undergo evolution and transmit within a new host. Yet, there is evidence that some RNA viruses have developed host specialization and that rates of variation of DNA viruses should not be underestimated in comparison to RNA viruses. Because viruses are able to undergo various mutations, this increases their ability to infect new hosts but in the long run reduces their fitness in the donor host. By observing Figures 2 and 3 in the article, this is deemed fitness trade-off. However, not all mutations cause a reduction in fitness trade-off for there are a few advantageous ones that increase fitness. Also, when only a few adaptive mutations are required between donor host and recipient host, transmission becomes more efficient. As far as emergence and successful host transfer are concerned, the modes of virus transmission cause limitations. For example, if viruses are not able to survive between donor, recipient and or vector hosts, then emergence becomes a challenge. Furthermore, different pathways of transmission either by droplet spread, sexual inoculation and or fecal-oral represent challenges in accommodating various hosts. Recombination and reassortment make viruses more susceptible to genetic changes that are beneficial in the long run. In comparing RNA and DNA viruses, the possibility of recombination varies but in observing the retrovirus HIV, there is a high rate of recombination which may correlate to its effective emergence. Figure 5 examines possible roles of recombination in the HIV virus as well as its origin from other primates. Another example of a recombination virus can be viewed in SARS CoV which most likely arose from a combination of a CoV virus and another bat virus before infecting human hosts. Once a virus has been able to switch to a new host, it further uses recombination and reassortment in the process of adaptation. Lastly, there have been cases in which viral intermediates with lower fitness were required in the process of successful transmission. Aside from viruses adapting to their new hosts they also have to optimize their intensity in the host cells at the same time evading any immune responses. By being able to detect viruses that do not spread efficiently, there would be a greater chance of controlling epidemic outbreaks.
Reading through this scientific journal, the main purpose of the article is to present the audience with information on how viruses are able to cross species and bring about new epidemic diseases. The authors mostly define the barriers that a virus has to overcome in order to obtain successful transmission and overall emergence by organizing the information into various subheadings. For example, in the section Environmental and Demographic Barriers to Host Switching, the authors compare human actions such as travel or trade and link these to viral host switching and the potential for infection. In the next section, they focus on the host and the barriers that the virus has to overcome in order to give rise to efficient transmission. Basically the virus has to be able to enter into potential host cellsand in doing so has to bind to receptors and then either fuse or undergo endocytosis. However, host cells have various mechanisms by which they are able to stop a virus from spreading and causing further infections. Next, there is a discussion about the relationship between the host range of a virus and whether or not it is a factor in determining the likelihood of host switching. The authors state that regardless of the host range of a virus, both generalist and specialist viruses have been successful in transmission into a new host. Lastly, the authors examine mutations and adaptations of viruses in response to their ability to emerge and cause diseases. These last few paragraphs consider what occurs once a virus has entered into a host cell and its ability to maintain entry by undergoing advantageous mutations or further adapting to the recipient hosts. The article ends with a basic summary or overview of all the information presented earlier with the outlook of being able to control future epidemic diseases. Upon reading this journal article, the style of writing is rather complex in certain sections which would inhibit the audience from fully understanding the material. Also, there appear to be no major experiments or tests conducted by the authors for the journal article only contains basic information and referenced data. Further, in quite a few sections, the authors use phrases such as, “poorly understood” and “we know relatively little” in discussing the information. This would most likely make the audience skeptical as to the authors' competence and understanding of the information being presented. In addition, while presenting their information, the authors mainly focus on few specific viruses such as HIV, SARS and Influenza. What about the rest? Are other viruses less prone to host switching or crossing barriers? These aspects need to be addressed so that the audience is not able to ponder and make generalizations. Lastly, no solution is stated as to the prevention of future epidemics from the possibility of viral host switching. The only statements made in the journal consisted of being able to better understand the information presented and the complexities that follow this topic. Overall, this article should only be used as background information in aiding previous knowledge on the topic. The authors accomplish the task of providing the audience with information, but the style and the presentation should have been executed differently.
51Due原创版权郑重声明：原创范文源自编辑创作，未经官方许可，网站谢绝转载。对于侵权行为，未经同意的情况下，51Due有权追究法律责任。
51due为留学生提供最好的作业代写服务，想获取更多Essay代写范文，亲们可以进入主页 www.51due.com 为留学生提供essay辅导服务，了解详情可以咨询我们的客服QQ:800020041哟。-lc
