Chicken pox is a common and usually mild childhood disease caused by the varicella virus. The same virus is also the cause of a very painful skin rash known as shingles in adults. These two very different illnesses demonstrate the two missions of all viruses – to reproduce themselves and to stay alive. Reproduction keeps the varicella virus spreading from child to child. Hibernation keeps it alive in adults, giving it another chance to reproduce. While chicken pox is usually a mild disease, shingles is painful and at times disabling.
Since 1995, vaccination against the varicella virus has been very successful in reducing the number of childhood chicken pox cases. In 2005, a vaccine designed to boost adult immunity cut the number of cases of shingles in adults in half and a vaccine about to be introduced now, in 2017, promises much better protection against shingles for older adults, especially for older adults. Both chicken pox and shingles vaccines mark significant progress against the varicella virus, which infects 95% of unvaccinated people.
Who gets shingles
Shingles typically afflicts older people or in people with weakened immune systems. In them, the long-sleeping varicella virus has suddenly awakened, erupting in an intensely itchy, blistered rash known confined to one patch of skin, usually on the trunk, but sometimes on the head or extremities. Doctors call shingles herpes zoster, which sometimes causes confusion with the common cold sore, caused by the herpes simplex virus. Both herpes simplex and varicella viruses are members of a larger family of “alphaherpes” viruses, with similar abilities to live in peace inside the body and revive periodically.
Why name it shingles?
Shingles is a more descriptive name than herpes zoster. When fully developed and severe, the shingles rash has a rough, red, pebbled surface formed by multiple blisters packed in tight formation, often rectangular in shape. Like a roof shingle, the patch of virus- laden blisters can look like it has been laid on top of the skin. The distribution of this adult eruption of the varicella virus is very different from the random and widespread distribution of blisters in chicken pox. The difference between rashes caused by exactly the same virus is a visual lesson in the way the varicella virus infects, reproduces, goes into hiding and reemerges.
The initial infection: chicken pox
The varicella virus enters the body through the nose or mouth. It is picked up by immune cells in the lymphatic fluid and then makes its way through the rest of the body in a trip that takes 7-10 days. Since the immune system doesn’t see the virus as much of a threat, there are often no symptoms of any illness in this period. But once the virus reaches the skin, real battle begins. Troops of immune cells produce small red dots on the skin, then red bumps and finally blisters which rupture and release new viral particles to the air. Mission number one, reproduction is accomplished.
The virus goes into hiding
Mission number two, staying alive, is more complicated. While varicella viruses spread easily from ruptured blisters or via coughing and sneezing, once the viruses dry out, they die. Dried, crusted rashes are no longer contagious. But underneath the skin, some viruses begin another journey. They travel up long thin nerve fibers that carry sensory information from the skin to the spinal cord. Their first stop is the nerve cell bodies that sit in little clumps of tissue called ganglia, just outside the spinal cord. Here, for reasons that are unknown, the viruses are allowed to integrate their genetic material into the nucleus of the cells, alongside the DNA and RNA responsible for normal protein production.
For years, varicella viruses demand nothing of their host nerve cells. Then in later life, or sooner in people who have suppressed immune systems from diseases like AIDS or treatment of diseases like cancer, the varicella virus may suddenly commandeer the protein-making machinery in the ganglionic nerve cell. It makes multiple copies of itself, sending them back out to the skin along the same nerves by which they entered the ganglia. The rash that appears affects only the part of the skin innervated by those nerves. The sensory nerves are arranged in “stripes” around the trunk and down the limbs, and the rash looks like a portion of that stripe.
Why the re-awakened virus causes so much pain
Pain is a central feature of shingles because the immune system attacks the virus for a second time. This time, the attack starts in the ganglia where the virus has emerged from hiding. When the immune battle against the virus begins, the nerve cells report the action to the brain, even before a skin rash appears. The unwitting patient begins to feel sharp and shooting pains, as well as numbness, tingling and itching sensations in the skin as long as two or three days before a rash appears. Occasionally fever, headache and back pain appear. Sometimes pain remains even after the rash resolves, a distressing condition called post-herpetic neuralgia, which is often difficult to manage.
Pain is not the only complication of shingles. Permanent damage may result from re-emergence of the virus in a sensory distribution that involves organs other than skin. Rashes that involve the eye can cause scarring the cornea, and those that involve the ear sometimes cause permanent deafness. Shingles cannot be transmitted, but if someone who has never had chicken pox or been vaccinated against it comes in contact with blister fluid from the shingles rash, they will get chicken pox. Adult chicken pox is a far worse illness than the pediatric version.
Immunity to the chicken pox virus diminishes with age, and shingles rarely appears before the late 50s. About one in every three people who’ve had chicken pox will get shingles; the risk of a second episode is also about one in three and higher if pain persists more than 30-60 days. Recurrences rarely happen more than twice, indicating that the reawakened virus stimulates renewed immunity.
Avoiding the often disabling pain of an acute shingles episode and diminishing the risk of post-herpetic neuralgia are both good reasons to consider adult immunization against the chicken pox virus. Not only does the adult vaccine cut the risk of getting shingles in half, it makes cases that do occur significantly less severe. The large study that yielded these results also turned up no vaccine safety issues. When you next think about getting a flu shot, give some consideration to prevention of shingles too.