Herpes simplex virus (HSV) is a DNA virus that causes oral and perioral wounds. Both herpes subtypes can cause these sores.
Herpes simplex virus (type 1, herpes-1 or HSV-1) causes about 80% of oral herpes infections. There is no evidence that the HSV-1 virus is mutated to the HSV-2 virus.
Another herpes simplex virus (type 2, herpes-2 or HSV-2) causes the other 20% and causes most genital herpes infections.
These herpes viruses enter the body through small incisions in the skin or mucous membranes, which can scratch or break. The incubation period for herpes simplex infection is approximately three to six days. The spread (transmission) of a virus is a person-to-person relationship. If there is a blistering or disease, it is more likely that the virus will spread. Most people enter (with or without obvious lesions) after uninfected persons come into direct contact with the person carrying the virus. Simple contact with infected people is often the way children are exposed. Adolescents and adults are often exposed through skin contact, but may be exposed through kissing or sexual contact (oral and/or genital contact), especially HSV-2. Statistical studies show that about 80%-90% of people in the United States have been exposed to HSV-1, and about 30% have been exposed to HSV-2. Under normal circumstances, the infectious period continues until the lesion heals. Some people (estimated from 30% to 50%) occasionally emit herpes virus with little or no relevant symptoms or signs.
Oral lesions (and genital lesions) may reoccur. This occurs because the HSV virus is still alive, but it is present in nerve cells in a quiet, inactive (sleep) state. Occasionally, the physical condition (see stage 3 above) causes the HSV to actively reproduce, leading to new lesions.
HSV viruses multiply in human cells by transcending and utilizing most of the human cell functions. One of the HSV steps in proliferation is to control the nuclei of human cells and change their structure. Altered nuclei (enlarged and lobed or multinucleated) are actually used to aid in the diagnosis of herpes simplex infections by microscopic examination. The reason for the appearance of ulcers is that when they mature, many HSV particles break the membrane of human cells when the cells break.
The transmission of HSV-1 occurs through direct exposure to saliva or droplets formed in the breath of infected individuals. In addition, skin contact with the lesions of infected individuals can spread the disease to another person. Although viral transmission usually requires close personal contact, HSV-1 may be transmitted when people share toothbrushes, drinking cups or tableware.
