Virus latency
Virus latency (or viral latency) is the ability of a
Virus latency is not to be confused with
Mechanisms
Episomal latency
Episomal latency refers to the use of genetic
Herpesviridae
One example is the
Epstein-Barr virus
The
Herpes simplex virus
In the case of herpes simplex (HSV), the virus has been shown to fuse with
Cytomegalovirus
Cytomegalovirus (CMV) establishes latency in myeloid progenitor cells, and is reactivated by inflammation.[9] Immunosuppression and critical illness (sepsis in particular) often results in CMV reactivation.[10] CMV reactivation is commonly seen in patients with severe colitis.[11]
Advantages and disadvantages
Advantages of episomal latency include the fact that the virus may not need to enter the
Disadvantages include more exposure to cellular defenses, leading to possible degradation of viral gene via cellular
Reactivation
Reactivation may be due to stress,
Proviral latency
A provirus is a virus genome that is integrated into the DNA of a host cell.
Advantages and disadvantages
Advantages include automatic host cell division results in replication of the virus's genes, and the fact that it is nearly impossible to remove an integrated provirus from an infected cell without killing the cell.[14]
A disadvantage of this method is the need to enter the nucleus (and the need for packaging proteins that will allow for that). However, viruses that integrate into the host cell's genome can stay there as long as the cell lives.
HIV
One of the best-studied viruses that does this is
Maintaining latency
Both proviral and episomal latency may require maintenance for continued infection and fidelity of viral genes. Latency is generally maintained by viral genes expressed primarily during latency. Expression of these latency-associated genes may function to keep the viral genome from being digested by cellular
An example of such a gene product is the
A certain type of latency could be ascribed to the endogenous retroviruses. These viruses have incorporated into the human genome in the distant past, and are now transmitted through reproduction. Generally these types of viruses have become highly evolved, and have lost the expression of many gene products.[18] Some of the proteins expressed by these viruses have co-evolved with host cells to play important roles in normal processes.[19]
Ramifications
While viral latency exhibits no active
More serious ramifications of a latent infection could be the possibility of transforming the cell, and forcing the cell into
Human papilloma virus
This is also seen with infections of the
HIV
In the field of HIV research, proviral latency in specific long-lived cell types is the basis for the concept of one or more viral reservoirs, referring to locations (cell types or tissues) characterized by persistence of latent virus. Specifically, the presence of replication-competent HIV in resting CD4-positive T cells allows this virus to persist for years without evolving despite prolonged exposure to antiretroviral drugs.[24] This latent reservoir of HIV may explain the inability of antiretroviral treatment to cure HIV infection.[24][25][26][27]
See also
References
- ^ Villarreal, Luis P. (2005). Viruses and the Evolution of Life. Washington, ASM Press.
- ^ N.J. Dimmock et al. "Introduction to Modern Virology, 6th edition." Blackwell Publishing, 2007.
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