Varicella Zoster Virus

Varicella zoster virus is a member of the alphaherpesvirus group and is the cause of both chickenpox (also known as varicella) and shingles (herpes zoster).

The virus is surrounded by a covering, or envelope, that is made of lipid. As such, the envelope dissolves readily in solvents such as alcohol. Wiping surfaces with alcohol is thus an effective means of inactivating the virus and preventing spread of chickenpox. Inside the lipid envelope is a protein shell that houses the deoxyribonucleic acid.

Varicella zoster virus is related to herpes simplex viruses types 1 and 2. Indeed, nucleic acid analysis has revealed that the genetic material of the three viruses is highly similar, both in the genes present and in the arrangement of the genes.

Chickenpox is the result of a person's first infection with the virus. Typically, chickenpox occurs most often in children. Recovery is usually complete within a week or two and immunity to another bout of chickenpox is usually, but not always, life-long. Treatment for chickenpox is available. Fortunately for adults, a vaccine to chickenpox exists for those who have not contracted chickenpox in their childhood.

Naturally acquired immunity to chickenpox does not prevent someone from contracting shingles years, even decades later. Shingles occurs in between 10% and 20% of those who have had chickenpox. In the United States, upwards of 800,000 people are afflicted with shingles each year. The annual number of shingles sufferers worldwide is in the millions. The disease occurs most commonly in those who are over 50 years of age.

As the symptoms of chickenpox fade, varicella zoster virus is not eliminated from the body. Rather, the virus lies dormant in nerve tissue, particularly in the face and the body. The roots of sensory nerves in the spinal cord are also a site of virus hibernation. The virus is stirred to replicate by triggers that are as yet unclear. Impairment of the immune system seems to be involved, whether from immunodeficiency diseases or from cancers, the effect of drugs, or a generalized debilitation of the body with age. Whatever forces of the immune system that normally operate to hold the hibernating virus in check are abrogated.

Reactivation of the virus causes pain and a rash in the region that is served by the affected nerves. The affected areas are referred to as dermatomes. These areas appear as a rash or blistering of the skin. This can be quite painful during the one to two weeks they persist. Other complications can develop. For example, shingles on the face can lead to an eye infection causing temporary or even permanent blindness. A condition of muscle weakness or paralysis, known as Guillian-Barre syndrome, can last for months after a bout of shingles. Another condition known as post herpetic neuralgia can extend the pain of shingles long after the visible symptoms have abated.