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There are three types of persistent infections, latent, chronic and slow, in which the virus stays inside the host cell for prolonged periods of time. During latent infections there is minimal to no expression of infected viral genome. The genome remains within the host cell until the virus is ready for replication.
Some viruses can "hide" within a cell, which may mean that they evade the host cell defenses or immune system and may increase the long-term "success" of the virus. This hiding is deemed latency. During this time, the virus does not produce any progeny, it remains inactive until external stimuli—such as light or stress—prompts it to activate.
Finally, the host restriction for human viruses makes it unethical to experimentally transmit a suspected cancer virus. Other measures, such as A. B. Hill's criteria, [10] are more relevant to cancer virology but also have some limitations in determining causality. Simplified diagram of the structure of the Epstein–Barr virus (EBV).
The potential of viruses as anti-cancer agents was first realised in the early twentieth century, although coordinated research efforts did not begin until the 1960s. [7] A number of viruses including adenovirus, reovirus, measles, herpes simplex, Newcastle disease virus, and vaccinia have been clinically tested as oncolytic agents. [8]
The variety of host cells that a virus can infect is called its host range: this is narrow for viruses specialized to infect only a few species, or broad for viruses capable of infecting many. [13]: 123–124 Viral infections in animals provoke an immune response that usually eliminates the infecting virus.
At the same time, viruses have co-evolved evasion machinery to address the many ways that host organisms attempt to eradicate them. DNA and RNA viruses use complex methods to evade immune cell detection through disruption of the Interferon Signaling Pathway, remodeling of cellular architecture, targeted gene silencing, and recognition protein ...
Each type of protein is a specialist that usually only performs one function, so if a cell needs to do something new, it must make a new protein. Viruses force the cell to make new proteins that the cell does not need, but are needed for the virus to reproduce. Protein synthesis consists of two major steps: transcription and translation. [34]
Viruses need to establish infections in host cells in order to multiply. For infections to occur, the virus has to hijack host factors and evade the host immune response for efficient replication. Viral replication frequently requires complex interactions between the virus and host factors that may result in deleterious effects in the host ...