What is a latent infection?

A latent infection is a situation in which a virus is present in the body, but remains dormant, without causing any obvious symptoms. The patient is still infected with the virus, and he or she can transmit the virus to others when they are exposed to the latent virus. Latent infections can also be activated, causing symptoms and illness to resurface. A classic example of a latent infection is herpes simplex, which flares up periodically to cause cold sores before going back to sleep.

People sometimes confuse latent infections with latency. Latency or clinical latency is one of the things that occurs during the incubation period of an infection, in which the causative agent is present in the body and multiplies, but does not cause symptoms. The virus involved in clinical latency is not dormant, as is the case with latent infections, but is fully active and causing problems for the host organism. Eventually, the virus will come out of dormancy and begin to cause detectable symptoms, alerting the host to the fact that an infection is occurring.

Some infections can never be completely cleared from the body, becoming dormant with the use of medications and other measures to control the virus and inhibit replication. In these cases, the latent infection may flare up periodically in response to environmental cues. Latent infections can also be caused when a virus mutates, becoming impossible to eradicate, or when a course of treatment is not completed, allowing a virus to lie dormant in the body.

Several viruses are characterized by causing a latent infection, allowing the virus to ebb and flow in the body in cycles as the environment changes. From a virus point of view, the ability to remain dormant is critical, as it allows the virus to retain a host while dormant when conditions are hostile or unpleasant for the virus. Latent infections can also be very difficult to detect or manage.

As well as causing problems for the host by periodically becoming inflamed and causing a host of symptoms, latent infections can become more sinister. A number of viruses have been linked to runaway cell division, which is likely caused by viral and cellular DNA encoding leading to crossed wires and unrestrained cell division. Latent infections can also become a serious problem when a patient becomes immunocompromised, as latent infection can manifest when the patient's immune system passes a critical point.

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