Discuss mechanisms of viral persistence illustrating your answer with specific examples

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Discuss mechanisms of viral persistence illustrating your answer with specific examples

Viruses have acquired mechanisms to persist in human hosts even if antiviral drugs are applied to block significant stages in the virus cycle. Strategies are developed by viruses to 'evade, escape and survive' to fight against the host's immune system so that pathogens are able to persists and their purpose can be continued. Usually this type of strategy is employed by the 'hit and stay' viruses and their ultimate aim is to gain long residence in the host's body. Viral reservoirs represent a major problem with terminating infections as the drugs are no longer effective in virus clearance. This could lead to chronic infections, which can be divided into two kinds: The chronic persistent infection and viral latency. In the first type there is continuous replication of the virus from the time of the host being infected primarily and usually associated with virus evolution. The latter type of infection shows a long period of viral suppression as the viruses reduce their expression by displaying only a limited number of viral proteins.

Another type of virus strategies are the 'hit and run' infections, which does not often cause persistence but continuous reoccurrence. The viruses are highly infective with the ability to escape to new hosts before the attack of the old infected host's immune system. Thus this type of infections is readily transmitted and includes the influenza viruses and the rhinoviruses of the common cold. Continue mutation of antigenic specificity and rapid transmissions from hosts to hosts enables the influenza virus to infect and reoccur continually. Often once viruses had gained access inside the hosts, the normal immune response would be host shut off. However, viruses have developed ways to fight against this normal cell response and they are able to replicate selectively and translate their viral gene material bringing "the release of infectious viral progeny". For example, the influenza viruses use the method of attacking the host's mRNA translation machinery by inactivating the initiation site of mRNA translation: the eIF4E protein and ribosomal binding to the capped RNA will stop. This protein complex also contains poly A binding protein - protein PABP, which is responsible for the circularization of mRNA to facilitate reinitiating translation process and promotes protein synthesis of host's. Rather than using the normal viral IEF ribosomal complex, the virus acclimate the normal cellular protein GRSF-1 and these enables viral RNA translation to carry on. This is one example to portrait the escape of human host's immunity to continue viral infection.
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Viruses could also escape immunological attack by hiding at privileged sites, for example inside the brain in which the blood brain barrier act as a source of protection where the host's immune system is unable to detect the virus or can take no action to remove the virus. Presence of antigenic proteins brings about recognition and activates the immunological functions of cytotoxic T cells and T helper cells against pathogens and viruses. However, strategy have been developed by viruses that for some viral proteins, the endogenous or exogenous pathways of antigen presentation can be interfered. This may lead ...

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