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The most sought-after answer to the question – what is shingles – is one that addresses its cause, clinical features and whether or not it is contagious. The cause is fairly straightforward. The reason it occurs is not though. The clinical features are the signs and symptoms it causes. Shingles is not contagious. But the cause of it is.
Shingles is reactivation of the virus that causes varicella. Varicella is a more formal name for chickenpox. The name of the virus is varicella-zoster virus (VZV). It belongs to the herpes family of viruses. Therefore, the alternate and more formal medical name for shingles is herpes zoster. VZV causes both shingles and chickenpox. In the case of chickenpox, the infection is primary or initial. Shingles on the other hand is a secondary or recurrent infection.
Shingles is not to be confused with the sexually transmitted herpes disease though. The latter is the result of infection with a different virus of the herpes family. The name of that virus is herpes simplex virus.
What causes shingles to occur?
It is impossible to develop shingles without having first had chickenpox. When chickenpox recedes the viruses that cause it migrate up nerve fibers to settle in the ganglia of cranial nerves and the dorsal root ganglia of sensory spinal nerves which shield them from the blood stream and antibodies. The viruses exist dormant (inactive) in the ganglia unless something activates them. Once activated they move back down nerve fibers and begin replicating. Upon reaching the nerve endings in the skin they cause the classic signs and symptoms of shingles.
The specifics of what triggers VZV to become active are unknown but the mechanism involves some dampening of cell-mediated immunity. That explains why the incidence of shingles increases with age, given the fact that cell-mediated immunity wanes with age. In fact, more than half of unvaccinated people 85 years of age and older have had or will have a bout of shingles. Other indications that a decline in cell-mediated immunity is involved in the onset of shingles are the following:
- The increased incidence of shingles with conditions that suppress the immune system, such as HIV infection and many forms of cancer
- The increased incidence of shingles in patients treated with immunosuppressive drugs such as corticosteroids
- The tendency of the herpes zoster rash to be disseminated (widespread) because of involvement of several dermatomes in people with suppressed immune systems
- Prevention of shingles in people 60 years of age by the herpes zoster vaccination, providing their immune systems are not compromised
Signs and symptoms of shingles
The main signs and symptoms of shingles involve the skin. But they may be preceded or accompanied by any or a combination of the following:
Abnormal skin sensations (i.e. itching, tingling, or pain) usually precede the typical rash. The pain at this stage is often dull. It may be like a toothache, muscle ache or headache. As the rash later evolves, the pain which coincides the distribution of the rash, may remain the same or it may change in terms of quality or intensity compared to the onset. Many patients describe the pain at this stage as burning, stinging, stabbing, or throbbing.
The classic rash usually appears two or three days after the abnormal skin sensations begin, but
might lag for up to two weeks. It typically starts out as a reddened maculopapular outbreak. That means it consists of small spots, some of which are flat, others in the form of raised bumps. New lesions appear over the next three to five days. They spread in a proximal to distal direction and usually follow the path of a single sensory spinal nerve, on one side of the body.
The initial rash evolves into vesicles (tiny blisters) which become cloudy and eventually scab or crust over in seven to ten days. One patient might have best described the rash at this stage as he reminisced about his own experience. His comment was, “I see why they call it shingles. It looked like and felt like the shingles on a roof.” The lesions usually heal within two to four weeks after their onset. But they often leave scarring and changes in skin color.
The rash most commonly occurs between the T1 and L2 dermatomes. That means in the skin regions between the upper chest and the lower abdomen or the inner arms. In about 15% of the cases the rash follows the path of the upper division of cranial nerve V. In addition to causing a painful swollen rash of the upper face including the forehead and eyelids, shingles in this area can damage the eye and threaten vision.
The pain may or may not fully subside with the resolution of the rash. In some patients it lingers for several days after the rash has disappeared. Postherpetic neuralgia is sustained pain for at least 90 days after the rash has ceased. It is a complication that 20% of people with shingles experience. Most cases of it occur in patients 50 years of age and older.
Is shingles contagious?
Shingles is not contagious, given the fact that a person with it cannot transmit that disease to someone else. The virus is contagious though in that a person with shingles can transmit VZV to someone who has never had exposure to it, in which case that person can develop chickenpox. Shingles cannot spread from a person who actively has it to a person who has had chickenpox before though. The reason is the latter has some natural immunity against VZV by virtue of having had chickenpox.
To end on a bright note, the passage of VZV might be beneficial with regard to older people contracting it. The thinking is that contact with the virus might boost their waning immunity against it. If this is correct, the exposure to it serves as a quasi-vaccination to prevent a future bout of shingles. This notion is theoretical but not proven at this point.