Latent - A Hidden or Dormant Infection

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Herpes Virus, artwork. David Mack/Science Photo Library/Getty Images

Definition: A latent infection is an infection that is hidden, inactive, or dormant. As opposed to active infections, where a virus or bacterium is actively replicating and potentially causing symptoms, latent infections are essentially static. While an infection is latent, it may hide from the immune system and/or be difficult to treat with drugs and other therapies.

Also Known As: Dormant/Inactive

Examples: Herpes infections go through latent periods where individuals don't have any outbreaks.

The Relevance of Latent Infections to Understanding STDs

Many sexually transmitted diseases, defined as conditions that are primarily spread through sexual or intimate activities, go through periods of latency, where clients are asymptomatic and the infection is lying dormant in their bodies (although it may still be transmittable to a partner.) This is one of the reasons that STDs are a hidden epidemic.The latent infection periods potentially provide opportunities for these conditions to spread unrecognized when the infection reactivates before symptoms appear.

The two STDs that are the focus of most discussions of latency are herpes and HIV. However, even though both infections have latent periods, the biology of the two types of latency period is somewhat different. When looking at herpes, the infection is often said to be latent between outbreaks of cold sores or genital disease.

The thing is, not all herpes infections are truly latent in those periods. Often the infection activates enough for asymptomatic shedding, and asymptomatic transmission, but not enough to cause noticeable or recognizable symptoms.

Latent HIV, in contrast, is a more quantitative definition, since symptoms of HIV are indirect rather than direct consequences of infection.

In other words, most symptoms are caused by opportunistic infections that take advantage of the immunosuppression caused by HIV rather than by HIV itself. Therefore, HIV is considered to be latent when the retrovirus is not actively making copies of itself in the body. The HIV living in the viral reservoir and not reproducing is latent.

When doctors and scientists talk about a functional cure for HIV, they are talking about a treatment regimen that will eradicate all active virus and establish a permanently latent infection. A true cure would also need to eliminate all the latent virus and provirus in the viral reservoir, and while that's something that scientists continue to work on, it's likely still a few years off.

Sources:

Cohn LB, Silva IT, Oliveira TY, Rosales RA, Parrish EH, Learn GH, Hahn BH, Czartoski JL, McElrath MJ, Lehmann C, Klein F, Caskey M, Walker BD, Siliciano JD, Siliciano RF, Jankovic M, Nussenzweig MC. HIV-1 integration landscape during latent and active infection. Cell. 2015 Jan 29;160(3):420-32. doi:10.1016/j.cell.2015.01.020

Kramer MF, Cook WJ, Roth FP, Zhu J, Holman H, Knipe DM, Coen DM. Latent herpes simplex virus infection of sensory neurons alters neuronal gene expression. J Virol. 2003 Sep;77(17):9533-41.

Siliciano JD, Siliciano RF. Recent developments in the search for a cure for HIV-1 infection: targeting the latent reservoir for HIV-1. J Allergy Clin Immunol. 2014 Jul;134(1):12-9. doi: 10.1016/j.jaci.2014.05.026.

Steiner I, Kennedy PG. Herpes simplex virus latent infection in the nervous system. J Neurovirol. 1995 Mar;1(1):19-29.

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