Introduction To Virology

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Viruses are obligate intracellular parasites because they are unable to replicate or carry out their life cycle without infecting and using the cellular machinery of a host organism. They rely on the host's cellular resources to reproduce and spread. This obligate dependence on host cells distinguishes viruses from other types of parasites that can survive and replicate independently outside of a host.

Naked capsid viruses release from the cell by lysis, which means they cause the cell to burst open and release new virus particles. This is in contrast to enveloped viruses that bud off from the cell membrane. Naked capsid viruses are also sensitive to various environmental factors such as drying, heat, detergents, acids, and proteases, which can lead to their inactivation. They cannot survive in the gastrointestinal tract and do not spread easily via fomites, which are objects or materials that can carry infectious agents.

Viruses are unable to replicate DNA because they lack the necessary cellular machinery to do so. Unlike living organisms, viruses cannot carry out metabolic processes or reproduce independently. Instead, they rely on host cells to replicate their genetic material and produce new viral particles. Viruses can only replicate by hijacking the cellular machinery of the host organism. Therefore, they are unable to replicate DNA on their own.

The question asks for one type of viral diagnostic, and the answer provides four options: electron microscope, PCR, serology, and cytologic examination. These are all different methods used to diagnose viral infections. An electron microscope is a powerful tool that can directly visualize viruses. PCR (Polymerase Chain Reaction) is a technique used to amplify and detect viral DNA or RNA. Serology involves testing for the presence of antibodies produced by the immune system in response to a viral infection. Cytologic examination refers to the microscopic examination of cells for the presence of viral particles or changes caused by viral infection.

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The two types of symmetry for Naked Capsid Viruses are icosahedral and helical. Icosahedral symmetry refers to the arrangement of the viral capsid proteins in a symmetrical 20-sided shape, resembling a soccer ball. This type of symmetry is commonly found in many viruses, including adenoviruses and herpesviruses. Helical symmetry, on the other hand, refers to the arrangement of viral capsid proteins in a spiral or helical shape. This type of symmetry is commonly found in filamentous viruses, such as tobacco mosaic virus. Both types of symmetry play a crucial role in maintaining the structural integrity of the virus and facilitating its infectivity.