Chickenpox (Varicella)

Chickenpox is a mild infectious disease of childhood. As with many childhood illnesses, babies usually inherit immunity from their mothers. This natural protection is effective up to six months of age, but then gradually diminishes.

What does chickenpox look like? (Clinical Features)

The visible symptom of chickenpox is an eruption of vesicles (a rash) which is centripetal, that is largely affecting the trunk and thinning out towards the head and limbs. This may or may not be preceded, by one to three days, by a fever and malaise (prodrome). Crops of vesicles progress successively to pustules then scabs. The pustules are small watery blisters averaging one-eighth of an inch (3mm) in diameter. Though the rash is painless, it is itchy, tempting the child to scratch. This may lead to secondary bacterial infection and permanent scarring.

The disease tends to be more severe in adults with varicella pneumonia occurring more commonly than in children.

Incubation Period

The incubation period for chickenpox is approximately 14-21 days, and the child is probably not infectious for longer than a week after the rash appears. However, the child is infectious for as long as moist vesicles are present, and the child should be excluded from school until all spots have crusted over.

Neurological Complications

It is possible to get neurological complications, but although they are uncommon they are potentially serious. In about one case in 1000, encephalitis develops within a few days of the rash, and about one-third of such patients will be left with severe deficits or will die. Rarer complications include Guillain-Barre Syndromeand Reye's Syndrome.

People who are especially vulnerable

Chickenpox is particularly dangerous for people whose immune systems have been weakened or in non-immune newborn babies. Children with deficient immune systems (due, for example, to leukaemia, anti-cancer therapy or steroid therapy - for example, for nephrotic syndrome) are especially vulnerable. In such cases the virus disseminates throughout the body, involving many organs in addition to the skin and lungs.

What if I'm pregnant?

Chickenpox tends to be more serious in pregnant women and it may affect the foetus. The risk during the first half of pregnancy is that the foetus may develop 'congenital varicella syndrome', which involves scarring of the skin, hypoplasia of the limbs, and eye abnormalities; or may spontaneously abort. However, infections which occur immediately before or after a non-immune woman gives birth can be particularly dangerous. Since there is no maternal antibody present to protect the baby, it can die from disseminated varicella zoster (shingles).

Can I catch chickenpox twice?

The immunity that follows infection with chickenpox is lifelong. Second attacks of chickenpox are rare, although sub-clinical (no symptoms) or very mild re-infections can occur, particularly in patients whose immune systems have been compromised in some way.

Treatment (for mild childhood chickenpox)

For more severe forms see later at the end of the section on shingles.

No treatment other than isolation is required. Calamine lotion¹ may be applied to relieve itching, which will also minimise the possibility of secondary bacterial infection.

Shingles (Herpes-zoster)

About 250,000 people per year in the UK get shingles. Of these, about 100,000 are affected by postherpetic neuralgia (PHN) (see later).

Clinical Features

The name 'shingles' is derived from the Latin word Cingulum, which means a girdle. This refers to the distribution of the rash (fluid-filled vesicles) in a girdle-like eruption round one half of the trunk. This distribution corresponds to the area of skin supplied by the branches of one or more of the main spinal nerves as they follow the course of corresponding ribs from the backbone forward to the breastbone. Less commonly, the rash appears on the face or neck.

The onset is often accompanied by a fever which may last from two to four days. From the first there is pain in that area of skin supplied by the affected nerve, which means that the pain appears before the rash. The pain may be intense, in fact so painful that typically people can't bear clothes touching the affected area. This pain may last for a few weeks; and in frail and elderly persons it may persist for months or even years after the eruption has disappeared. This so-called 'postherpetic neuralgia' (PHN) occurs in half of all patients over 60 years of age.

In older persons, the disease may also affect the fifth nerve of the brain, giving rise to shingles on one side of the face and forehead. The condition is characterised by intense pain and is often followed by a particularly intractable form of neuralgia, and subsequent scarring is often severe.

In some cases there is ulceration of the front of the eyeball, which may be followed by scarring and marked impairment of vision. This is due to involvement of the trigeminal nervewhich supplies the skin of the face.

It is also possible for shingles to appear in other areas such as the thigh and upper arm.

Many people are surprised at how ill they feel with shingles and, as with many other virus diseases, depression is often a feature.

Complications

Motor paralysis and encephalomyelitis are rare complications.

Ramsay Hunt Syndrome II

First described by Ramsay Hunt in 1907, RHS II is a common complication of shingles and is caused by the spread of the varicella-zoster virus to facial nerves. The condition is characterized by intense ear pain, a rash around the ear, mouth, face, neck, and scalp, and paralysis of facial nerves (which may or may not be permanent). Other symptoms may include hearing loss (which also may or may not be permanent), vertigo and tinnitus. There may also be loss of taste due to dryness of the mouth and tongue, which may also be noticed in the eyes.

How do people get shingles? (Pathogenesis)

Shingles is a re-emergence of the chickenpox virus, which can occur many years after the original chickenpox infection.

The original infection with varicella (as a child) is believed to occur by contact as well as via the respiratory route, but little is known for certain about what happens to it during the incubation period.

The chickenpox rash itself results from multiplication of the virus in epithelial cells of the skin. During this primary attack, virions (individual virus particles) move to the ganglia (a kind of 'junction box' of nerves beside the spine along sensory nerves) probably spread in Schwann cells of the nerve sheath. It persists in the neurons (nerve cells) as naked viral DNA. When the virus is re-activated it is thought to descend the sensory nerve by the same means as it ascended, namely within the axon cylinder.

Who will get shingles?

Anybody who has ever had chickenpox can develop shingles, and most people do have chickenpox in childhood. Prior to the general introduction of chickenpox vaccine, 90-95% of the population in the United States would get chickenpox in childhood. (There is no reason to suppose that the rate would be dissimilar in the United Kingdom). The risk of any individual of developing shingles in his or her lifetime is 20%.

People who have not had chickenpox cannot get shingles (some people with shingles claim that they have never had chickenpox - but this probably means that their original bout of chickenpox was so mild that it was not noticed (sub-clinical) or that the patient has forgotten because it was so long ago).

Shingles is most likely to occur in older people and it affects 1% of the 50-60 year age annually, with the incidence rising rapidly after that. Around 60% of 85 year olds will have suffered an attack.

The condition is particularly prevalent in patients suffering from Hodgkins disease, lymphatic leukaemia or other malignancies, or following treatment with immunosuppresive drugs or irradiation of or injury to the spine.

What causes the virus to reactivate?

Usually the cause is a reduction in your body's natural resistance to disease, which may be caused by stress, through being generally 'run down', or occasionally, when the body's defences have been affected by certain drugs or other immune deficiencies.

As shingles is caused by reactivation of the dormant virus, it is possible to have shingles more than once.

Is shingles infectious?

You cannot do much to avoid shingles. It is not caught by contact with anyone with either shingles or chickenpox; it is merely reactivation of the virus with which you were infected as a child. However, it is possible for a person with shingles to transmit chickenpox to someone who has not had it before. Therefore it is advisable for a sufferer to stay away from other people, especially pregnant women and newborn babies, until the blisters have dried (usually about seven days).

Treatment

The main consideration with shingles is to take regular pain relief (an analgesic), possibly even an anti-inflammatory painkiller (non-steroidal anti-inflammatory drug - NSAID), provided these do not interact with any other medication you may be taking. Your General Practitioner (GP) may also prescribe an anti-viral agent such as acyclovir (Zovirax).

If any of the blisters become infected the GP may prescribe antibiotics, which may be a cream or taken by mouth.

In the case of very severe shingles, as in immunocompromised patients, interferons at very high dosage may be prescribed.

In cases of Ramsay Hunt Syndrome II, treatment may or may not be required. When treatment is required, antiviral drugs or corticosteroids may be prescribed. Vertigo may be treated with diazepam, a benzodiazepine.

Vaccines

Scientists from Japan and the USA in particular have been working on a live attenuated (weakened virus) vaccine for some years. Early studies showed that a single injection was able to provide protection in 95% of recipients. However, it was not clear how long the protection would last. The early vaccines occasionally induced fever and a rash in normal children, and more frequently in immunocompromised children (the intended target group for the vaccine).

Now, Merck and Company have developed a vaccine which commenced Phase III Clinical Trials in June, 1999.

Testing the Shingles Vaccine

This study is a 5.5-year randomised, double-blind, placebo-controlled efficacy trial to determine whether vaccination with live-attenuated Oka/Merck varicella-zoster decreases the incidence and/or severity of herpes zoster (HZ) and its complications in adults 60 years of age and older.

The study is being conducted by the United States' Department of Veterinary Affairs in scientific collaboration with NIAID² scientists and Merck and Company, which developed the vaccine.

Approximately 38,000 generally healthy volunteer subjects were recruited, age 60 and older, with no prior history of shingles.

Half of the people in the trial are receiving the vaccine, which is a more potent form of the chickenpox vaccine routinely given to children, while the remaining half are injected with a placebo³. Neither the participants nor the researchers know which substance an individual is getting. Dr Norberto Soto, lead investigator at the NIH⁴ Clinical Center study site, is quoted as saying,

We believe that by stimulating the immune system with a live but weakened varicella virus vaccine, shingles and its sometimes painful aftermath, post-herpetic neuralgia, may be prevented.

Further Information

Further information can be obtained from the following:

• Herpes Viruses Association
• Medinfo
• Guillain-Barré Syndrome Support Group UK