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  • 当前位置:文档库 > Exercise1

    Exercise1

    病毒学(双语)习题1

    一、阅读下述短文,然后回答问题(每个问题8分,中英文均可)

    In order to persist and evolve in nature, viruses need a large population of susceptible hosts and an efficient means of spread between these hosts. The normal route is termed horizontal spread. The most common route of entry and exit of viruses is the respiratory route. Following their inhalation, viruses usually infect and replicate in the epithelial cells of the upper and lower respiratory tract (e.g. rhinoviruses, coronaviruses, influenza, para-influenza and respiratory syncytial virus). The viruses produced in these airways exit their host via sneezing and coughing. Many viruses which enter and exit via this route are not 'respiratory viruses' (e.g. chicken pox, measles, German measles). In these cases the virus leaves the respiratory tract to set up infection in other target organs. The oral-gastrointestinal route is used mainly by those viruses responsible for gut infections (rotavirus, Norwalk virus and the enteroviruses, including polio and coxsackie viruses). Vast numbers of virus particles can be excreted in fecal material (e.g. in the order of 1012particles g-1), facilitating the easy spread of these viruses in conditions of poor sanitation. Thus, the drinking of contaminated water and consumption of contaminated shellfish or other food prepared by unhygienic food handlers are ways in which these viruses are spread.

    Whilst the skin normally provides an impenetrable barrier to virus invasion, infectious viruses can enter following trauma to the skin. This may be from the bite of an animal vector (e.g. rabies via an infected canine, yellow fever via an infected mosquito). HIV, hepatitis B and hepatitis C may be transmitted by the injection of blood or blood products either in the form of a blood transfusion, a needle-stick injury, or by intravenous drug abuse.

    Sexual transmission of viruses is an important route for the spread of HSV, the papilloma viruses and HIV.

    Viruses may also be transmitted vertically- that is, from mother to offspring via the placenta, during childbirth, or in breast milk. Examples are rubella virus (German measles) and cytomegalovirus (CMV), acquired by the mother during pregnancy and transmitted to the developing embryo, often leading to severe congenital abnormalities and/or spontaneous abortion. Some viral infections, for example, HSV infections, if acquired in utero or during birth can present as an acute disease syndrome in the neonate. In the case of HIV and hepatitis B transmission, the neonate may be born with an asymptomatic infection, the virus persisting in a carrier state and developing into disease much later.

    Questions:

    1.What does horizontal transmission mean? Please give examples.

    2.The skin normally provides good protection against virus infection. But sometimes viruses can infect

    through the skin. Please explain.

    3.What is the vertical transmission of a virus? Please give examples.

    As obligate intracellular parasites with very restricted genetic-coding capacity viruses rely heavily on utilizing the metabolic machinery of the cell for their replication. It was therefore considered by many that the concept of selective toxicity was an unattainable goal and that interference with viral replication would

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