When a herpes virus infects a human, the immune system recognizes the invader and sets out to destroy it. To evade the immune system, the virus "hides out" inside the nervous system, where it establishes "latency," or a period of inactivity. Of the eight types of herpes that infect humans, some only cause a one-time outbreak. Other types, such as Herpes Simplex Virus, Types 1 and 2, which cause cold sores and genital herpes, can cause frequent outbreaks. Herpes zoster most often causes just two outbreaks, though complications can occur.
Varicella
The virus that causes shingles, or herpes zoster, is known as Varicella-Zoster Virus, VZV, Herpes Zoster Virus and Human Herpes Virus-3. The virus causes two diseases. The first, which infects at least 90 percent of people in the United States, is chickenpox, or varicella, according to the University of South Carolina. The disease is highly contagious and approximately 90 percent of uninfected people who have not been vaccinated and who live with an infected person will develop the disease. Varicella is spread from person to person either through contact with a chickenpox sore, or through respiratory aerosols after an infected person has sneezed or coughed. For the first five to seven days after infection, the virus remains in the lungs without causing symptoms. After that, it travels throughout the body, and makes its way to the skin's surface, approximately 12 to 14 days after infection, where it causes a characteristic blister-filled rash that usually begins on the trunk and spreads to the neck and face, and to a lesser extent, to the arms and legs.
Zoster
Once chickenpox has run its course in an otherwise healthy individual, the virus will enter a state of latency, or inactivity. For many people, chickenpox will be the only disease caused by the virus. For others, shingles will develop. Shingles is a reactivation of the varicella-zoster virus. It forms a different kind of rash than chickenpox, called a dermatome, which appear as a band of blisters. The rash most often appears on one side of the chest, neck or face, and can cause severe pain. Age is a factor in developing shingles, with the disease being most common in those over the age of 50, according to Mayo Clinic, and up to half of people who reach the age of 85 having had shingles during their lifetime. Occasionally, shingles can occur in and around the eye. Called, ophthalmic shingles, it can lead to vision loss and sometimes blindness.
Postherpetic Neuralgia
While a rash is the main symptom of both diseases caused by the varicella-zoster virus, pain, sometimes severe pain, can be a long-term aftereffect of the reactivation of the virus. Postherpetic neuralgia occurs when nerve endings are damaged by the virus. Even after the blisters have cleared, the nerve fibers can send confused and exaggerated messages of pain to the brain. DermaNet NZ reports that postherpetic neuralgia can be difficult to treat.
