2 - Spread of virus A. Spread in the environment and...

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Spread of virus A. Spread in the environment and encounter its target animal B. Spread from epithelial surface to target organs (Immune system) C. Spread between host cells -Virus has no locomotion unit -Their small size allows them to spread between infected cells to healthy cells by diffusion and Brownian movement -Production of large amount of progeny virions with surfaces composed of many copies of structures that allow the virions to attach to susceptible cells. Viral receptor: Molecules on host cell that allow virus attachment. 1. Viral receptors could be proteins or carbohydrates located on the host cell membrane. (Table 4.1). Many receptor-binding sites are components of the extracellular matrix or adhesion molecules. 2. Cells bearing viral receptors are susceptible but not necessarily permissive to virus infection. 3. The same receptor can be used by more than one family of virus. E.g. CD4 for HIV and Herpervirus type 7. 4. A virus can bind to more than one type of receptors. E.g. FMDV can bind to integrin ( α v β 3 ) and heparan sulfate. 5. Virion binding can usually occur at 0 o C (but entry of virus does not). Thus infection of cultured cells can be synchronized by incubation at 4 o C first then shift to 37 o C. 6. The receptors are usually abundantly expressed on differentiated cells. 7. Reason: The first steps in virus attachment are governed by the probability that a virion and a receptor will collide, which depends on the concentration of virions and host cells (and the density of receptors). 8. The rate of attachment = k [V] x [H], where [V] is the concentration of virions, [H] is the concentration of host cells, and k i s t h e r a t e c o n s t a n t . The k value for animal viruses vary greatly (as mush as five order of magnitude). Thus, a 100 fold dilution of virus-cells mixture will decrease the attachment rate of 10000 fold. Tissue tropism (Host range of virus) : why different viruses can only infect their specific host cells? The concept of susceptible vs permissive host cells Susceptible host cells carry specific virus binding sites (receptors) that allow virus binding. Permissive host cells
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This note was uploaded on 10/28/2010 for the course SCI biol3214 taught by Professor Lam during the Spring '10 term at CUHK.

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2 - Spread of virus A. Spread in the environment and...

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