All members of Herpesviradae are viruses with double-stranded DNA, the same type of genetic material that humans have. This similarity allows dsDNA viruses to merge their genes with those of their host, and become a permanent parasite with the ability to repeatedly reemerge after initial infection.
Varicella zoster virus (VZV), also known as Herpesvirus 3, causes both chickenpox (varicella) and shingles (zoster) infectious rashes. The virus enters the body through the respiratory tract or the mucous membrane of the eye. It then multiplies within the cells initially infected, and then travels throughout the body, via the bloodstream.
Chickenpox: Varicella Infection
When a person is first infected with VZV, the infection manifests as chickenpox, itchy lesions that can cover the entire body. Although symptoms of chickenpox are rarely serious or deadly, the infection is highly contagious, and prior to the availability of a vaccine, transmission was difficult to prevent, since an infected individual is contagious before they develop skin lesions.
Lesions appear two to three weeks after exposure, and those infected can continue to transmit the virus to others until all of the skin lesions have crusted over. VZV are shed through respiratory droplets and through the fluid in active lesions.
Children typically have milder infections that do adults. This is thought to be due to the more developed immune system of adults causing a stronger immune response that is more damaging to the infected tissues. Children, by contrast, have less experienced immune systems that generate a weaker response to the virus. There is a vaccine available to prevent chickenpox.
Shingles: Herpes Zoster Infection
Like other herpesviruses, varicella zoster can become dormant, sometimes for decades. After initial chickenpox infection, the virus hides in sensory nerves, and may become active again if the immune system becomes suppressed due to illness, stress and aging.
When the virus reemerges, it travels down the nerve cells and results in an extremely painful rash. The rash is typically localized to one side of the body in the region of the virally-inhabited nerve. Although the outbreak usually lasts a week to ten days, some individuals continue to experience pain (known as post-herpetic neuralgia) even after the rash clears. Shingles is most common in people 60 years of age or older. There is a shingles vaccination, indicated to reduce the likelihood of developing this painful rash in people 60 years or older.
Can Someone Catch Chickenpox from a Person with Shingles?
Yes. Cases in which people contracted chickenpox from a person with shingles are what demonstrated that the same virus causes both infections. So someone who has not been vaccinated against chickenpox, or who has not had chickenpox previously, can catch the varicella zoster virus from a person with shingles lesions, although this type of transmission of the virus is not very common, as it requires direct contact with shingles lesions.
Can a Person Catch Shingles from Someone with Chickenpox?
No. Shingles is a reactivation of the varicella zoster virus. So a person can catch chickenpox from someone with chickenpox or shingles, but shingles only develops after a person has initially had the chickenpox. Likewise, someone cannot catch shingles from someone else with shingles.
Bauman, R. (2007). Microbiology with Diseases by Taxonomy. Pearson Benjamin Cummings.
Centers for Disease Control (2006) Shingles Vaccine: What You Need to Know.
National Foundation for Infectious Diseases (2009) Facts about Chickenpox and Shingles for Adults.
This article was originally published in Suite101 online magazine.