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sigh...给大家一个权威得好了
Viruses are the smallest of parasites; they are completely dependent on cells (bacterial, plant, or animal) to reproduce. Viruses are composed of an outer cover of protein and sometimes lipid, and a nucleic acid core of RNA or DNA. In many cases, this core penetrates susceptible cells and initiates the infection.
Viruses range from 0.02 to 0.3 µ; too small for light microscopy but visible using electron microscopy. Viruses can be identified by biophysical and biochemical methods. Like most other parasites, viruses stimulate host antibody production.
Several hundred different viruses infect humans. Because many have been only recently recognized, their clinical effects are not fully understood. Many viruses infect hosts without producing symptoms; nevertheless, because of their wide and sometimes universal prevalence, they create important medical and public health problems.
Viruses that primarily infect humans are spread mainly via respiratory and enteric excretions. These viruses (see Table 162-1) are found worldwide, but their spread is limited by inborn resistance, prior immunizing infections or vaccines, sanitary and other public health control measures, and prophylactic antiviral drugs.
Zoonotic viruses pursue their biologic cycles chiefly in animals; humans are secondary or accidental hosts. These viruses (see Table 162-2) are limited to areas and environments able to support their nonhuman natural cycles of infection (vertebrates or arthropods or both).
Some viruses have oncogenic properties. Human T-cell lymphotropic virus type 1 (a retrovirus) is associated with human leukemia and lymphoma. Epstein-Barr virus has been associated with malignancies such as nasopharyngeal carcinoma (see Ch. 87), Burkitt's lymphoma (see Ch. 139), Hodgkin's disease, and lymphomas in immunosuppressed organ transplant recipients (see Ch. 149). Kaposi's sarcoma-associated virus is associated with Kaposi's sarcoma (see Ch. 126), primary effusion lymphomas, and Castleman's disease (a lymphoproliferative disorder).
Slow viral diseases are characterized by prolonged incubations and cause some chronic degenerative diseases, including subacute sclerosing panencephalitis (measles virus), progressive rubella panencephalitis, progressive multifocal leukoencephalopathy (JC virus), and Creutzfeldt-Jakob disease (a prion disease). (See Slow Virus Infections, below, and Subacute Sclerosing Panencephalitis and Progressive Rubella Panencephalitis in Ch. 265.)
Latency--a quiescent infection by a virus--permits recurrent infection despite immune responses and facilitates person-to-person spread. Herpesviruses exhibit latency.
refference from
http://www.merck.com/mrkshared/m ... chapter162/162a.jsp
病毒是最小的寄生物;它们完全依赖细胞(细菌,植物或动物)而复制.病毒的外壳为蛋白质,有时为脂质,核心为RNA或DNA核酸.在许多情况下,核心穿入易感细胞并引起感染.
病毒大小从0.02μ~0.3μ,在光学显微镜下不可见,但在电子显微镜下可以看到.病毒可用生物物理和生物化学的方法鉴定.与大多数其他寄生物一样,病毒可以刺激宿主产生抗体.
有几百种不同的病毒可以感染人体.许多病毒刚被发现不久,它们的临床意义尚未完全认识.虽然许多病毒感染宿主而不引起症状,然而,由于它们广泛地,有时是全球性地存在,因此造成重要的医学和公共卫生问题.
[ 本帖最后由 zhangheng1020 于 2006-1-12 14:44 编辑 ] |
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