Please help with thorough explanations for these two questions. 1. When two viru
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Question
Please help with thorough explanations for these two questions.
1. When two viruses with similar capsids coinfect a cell, it is possible for virions to be produced where the capsid does not match the genome. This phenomenon is known as phenotypic mixing, the consequences of which is the expansion of the host range. One of the most recent viral outbreaks, SARS and bird flu can be attributed to this phenomenon.
Explain which one and show how this could have happened. Please explain in thorough detail and reasoning.
2. When two viruses with similar capsids coinfect a cell, it is possible for virions to be produced where the capsid does not match the genome. This phenomenon is known as phenotypic mixing. What could be the consequences of this mismatch with regard to future infections? Please explain in detail and give thorough reasoning.
Explanation / Answer
1. Phenotypic mixing might have occured in case of influenza virus. Let's imagine that the viral strain capable of infecting birds and the viral strain capable of humans are co-infecting pig. There is a possibility that there is phenotypic mixing resulting in formation of pseudovirion containing capsid of human virus (hence possess the attachment proteins capable of binding to human cells) and genome of bird virus. So, this particle will be able to infect human cells. (However, phenotypic mixing can result in only temporary expansion/alteration of host range. So in case of influenza virus genetic reassortment is the major phenomenon involved).
2. Phenotypic mixing can result in alteration of host range in the viruses. Let's imagine there is a virus 'A', which can infect hosts 1,2 and 3. Similarly, there is another virus 'B' which can infect the hosts viz. 3, 4 and 5. A major reason for host specificity in the virions is the presence (or absence) of specific binding protiens which can bind to specific receptors on the host cells. So, in the above case, the capsid of virus 'A' will have binding proteins for the receptors of hosts 1, 2 and 3. Similarly, the capsid of virus 'B' will have binding proteins for the receptors of hosts 3, 4 and 5. If we imagine a situation where both virus A and B have infected host cell type 3 and there is phenotypic mixing. It is possible that we end up with a viral particle with genome of A and capsid of B. In such a situation, this virion will be able to bind to the receptors of hosts 3, 4 and 5. So, the virion with genome of A which can infect the host 1,2, 3 only, will be able to infect host 4 and 5 also. (Such virion is termed as pseudo virion)