After becoming infected with the herpes simplex virus, the epithelial cells of the genitalia and/or oral mucosa are rapidly infiltrated with the virus which quickly replicates within the cells causing their degeneration and necrosis (death).
Clusters of painful, inflammatory fluid-filled vesicles or blisters may appear. The infective virions are contained in the clear fluids within these lesions, from which they may shed and infect others during sexual or skin-to-skin contact.
Once inside the body, the virus establishes a hidden or latent infection in certain target cells, specifically in the sensory nerves in the dorsal route ganglia. The virus particle and its core DNA gets incorporated within the nerve cell bodies where it remains latent or dormant, meaning that no new viruses are produced.
This latency is aided by the presence of a strip of RNA Latency Associated Transcript (LAT) that is replicated from an area of the viral DNA. This LAT RNA intereferes with the usual processes that may occur on viral infection of a host cell such as organized death or removal of the cell by the immune system.
Once a primary infection has subsided and the virus is latently established, infection may recur within the first year. This recurrence may be triggered by stress, menstruation, suppressed immunity due to HIV infection, chemotherapy, radiation therapy, or after organ transplant operations when immunnosuppressants may be taken. In addition, the presence of other infections and subsequent fever may also suppress immunity and lead to a recurrence of symptoms.
Reactivation of the oral sores are often therefore termed cold sores or fever blisters, because of their tendency to emerge when a carrier has a fever, common cold or upper respiratory tract infection, for example.
Among many individuals, there may not be any symptoms for years. However, the risk of transmission due to asymptomatic shedding of the virus remains. Asymptomatic shedding refers to shedding or transmitting of the virus to a non-infected person even though no symptoms are present.
Asymptomatic shedding presents challenges in the control and prevention of herpes infection.
In women who have been exposed to the herpus simplex virus during preganancy, there is a high risk of the mother transmitting the infection to her baby, through infected fluids secreted in the birth canal during childbirth. This is called neonatal herpes and can severely affect the baby's eyes, mouth and skin or even the brain and spinal cord. If the infection is severe, it may be life threatening.
Reviewed by Sally Robertson, BSc