Chicken pox

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Alternative name: Varicella

Chicken pox is very infectious and occurs worldwide as a childhood disease that lasts for 5 to 7 days.

Chicken pox starts with a fever and a widespread rash of small blisters (vesicles), which are usually distributed on the chest, back, face, and the arms and legs. Sometimes the disease can be more severe, affecting internal organs (especially the lungs and liver).

Almost all of us will have only one episode of chicken pox in our lifetime, if at all. Once you’ve recovered, you’ll have life-long immunity to chicken pox.

The virus that causes chicken pox (varicella-zoster virus or VZV) belongs to the herpes virus family. It usually takes about 14 days from the time you’re exposed to the chicken pox virus to the time when symptoms start to occur. Sometimes this period can be as short as 10 days, or as long as 21 days.

The preliminary symptoms of fever and headache usually begin 24 to 36 hours before the rash appears. The fever subsides a few days after the rash appears, and the rash usually lasts for 5 or 6 days. It then starts to scab, dry and fall off. The last dried-up scabs fall off by 10 days.

Like other members of the herpes virus family, the chicken pox virus never really leaves the host after recovery from the initial infection. Instead, it remains hidden in certain nerve cells, without causing any obvious illness. This hidden or “latent” virus may be reactivated later by a variety of causes such as stress, malnutrition, or advanced age.

The reactivated virus will cause an illness called shingles (herpes zoster). Shingles is a band of painful blisters, usually involving the skin on the side of the chest or abdomen. It may involve the face.

Who gets chicken pox?
Worldwide, chicken pox is one of the most common childhood infectious diseases. In countries with moderate climates like South Africa, most cases occur before the age of 10 years.

The epidemiology is, however, less well understood in tropical areas, where a relatively large proportion of adults are seronegative, according to the World Health Organization (WHO). People who are seronegative show no significant level of antibodies in their blood that indicates previous exposure to the chicken pox virus (varicella virus or VZV).

In Africa, risk factors for VZV include the rapidly increasing elderly population and a high HIV prevalence. Note that chicken pox is a vaccine-preventable infection, but that routine vaccination isn’t currently available in the South African public sector. Vaccination is readily available in the private sector.

Symptoms of chicken pox
The rash in chicken pox first appears as pinkish raised bumps a few millimetres across, usually on the chest or abdomen.

Within hours the bumps develop into very itchy blisters, containing a clear fluid. These blisters are known as vesicles. The vesicles break down quite rapidly and form crusts and scabs, but a new crop of vesicles appears just as the previous crop starts to crust.

Typically 250 to 500 vesicles will form during the chicken pox illness. The chicken pox rash is usually mostly clustered on the chest and abdomen, with fewer vesicles on the face and limbs.

Vesicles on the scalp may be accompanied by swollen lymph glands at the back of the neck. Along with the skin blisters, blisters may also occur in the mouth and throat, on the eyelids, and in the genital and anal areas. In these areas, the blisters tend to break down, forming painful ulcers.

Blisters in the mouth make eating or drinking difficult. The blisters usually stop forming by the 5th day of the rash, and most of these become crusted by the 6th day of the illness.

What causes chicken pox?
Chicken pox results when a person, usually a child but sometimes an adult, becomes infected with the varicella-zoster virus (VZV).

Following the infection, this virus spreads throughout the body, as shown by the appearance and distribution of the rash that may cover the entire body.

Once the chicken pox illness is over, the varicella-zoster virus persists in a person for the rest of their life (the same happens to its close relative, the herpes simplex virus). The virus remains dormant in certain nerves, usually in the spine.

Chicken pox can occur in anyone who hasn’t had the illness before, while shingles can only occur in someone who has previously been infected with chicken pox.

The varicella-zoster virus is present in throat secretions of a person immediately before and just after developing the chicken pox rash. These secretions can reach another person as airborne droplets.

The skin blisters of chicken pox and shingles contain infectious virus, which can reach the nose or mouth of another person by contact or touch.

Shingles (herpes zoster) is the result of reactivation of the varicella virus in one of the spinal nerves. The virus travels along the nerve, producing large blisters localised in the area that the nerve supplies.

Shingles therefore involves an area of skin that’s served by a single sensory nerve. This area of skin is known as a dermatome. The dermatomes that are commonly affected during a shingles attack are those on the chest, abdomen or face. Only one dermatome is affected in a particular individual at any one time.

While shingles can occur at any age, it usually occurs in the elderly due to the immune system’s “memory” of the virus reducing over time. The immune system may not be able to effectively control the dormant virus.

Anyone whose immune system is compromised also loses the ability to control this virus. Immune control can be reduced by stress, poor diet, immune suppression and chemotherapy treatment. Immune control is also reduced in transplant patients and HIV-positive people.

Risk factors for chicken pox
Close exposure or contact with someone with early chicken pox will put you at risk of infection. Even spending some time in the same room as a person with early chicken pox will put you at risk.

The highest risk is associated with living in the same household as a person with chicken pox. Nine out of 10 people who haven’t had chicken pox before will contract the disease under these circumstances.

Generally, children are least likely to have complications from chicken pox. Babies under one year old are more vulnerable and, from puberty onwards, teenagers and adults are more prone to severe chicken pox and its complications.

Certain groups of people are particularly at risk for severe chicken pox. Children and adults whose immune systems are compromised are at particular risk. Examples of conditions that compromise the immune system include various forms of cancer, leukaemia, lymphoma and HIV/AIDS.

Some drugs, such as high doses of cortisone used for severe asthma, arthritis and kidney disease, may also compromise the immune system.

Immune-compromised people are prone to:

  • An extensive and severe rash.
  • Possible damage to internal organs, including the liver and lungs.
  • Haemorrhagic chicken pox (which involves severe bleeding).
  • A prolonged course of the illness.

Chicken pox may even be fatal in immune-compromised people.

Course and prognosis of chicken pox
Chicken pox is usually a mild illness in children, and most healthy children have a self-limiting infection that clears up after about 7 to 10 days.

There are, however, a number of possible complications. But fortunately these are quite rare.

Chicken pox encephalitis may occur in about 1 in 1,000 cases, usually towards the end of the disease. If diagnosed early, treatment is available.

Chicken pox pneumonia is another possible complication, but is less common in children than in adults. Chicken pox pneumonia may be a very serious complication of chicken pox and may be fatal if not treated early, especially in adults. Fortunately, anti-viral treatment is now available to treat it.

How is chicken pox diagnosed?
Chicken pox is usually an easily recognisable disease because of the distinctive rash of blisters. For this reason, laboratory tests usually aren’t necessary.

If there’s doubt, a virology laboratory can do rapid tests on fluid obtained from a vesicle with a tiny needle and syringe, or on cellular material obtained by swabbing the raw base of a vesicle.

In situations of exposure to chicken pox, the knowledge that a person has definitely had chicken pox before is useful when deciding what measures, if any, need to be taken. Often this information isn’t known or is incorrect, such as when adults try to recall whether they had chicken pox as a child.

In circumstances where an at-risk person has been exposed to chicken pox, a blood test can be done to show whether they have antibodies to the varicella-zoster virus. The presence of antibodies means that they had chicken pox in the past and that they’re therefore wholly or partially protected (as with immune-compromised people).

How is chicken pox treated?
In children, mild cases of chicken pox can be managed with simple measures to control the symptoms.

For itching:

  • Make sure your child wears loose cotton clothing.
  • Use cool, wet compresses to relieve itching.
  • Calamine lotion can be applied to the rash to help relieve itching, but avoid applying it to the child’s face.
  • Serve foods that are cold, soft and bland because chicken pox in the mouth can make drinking or eating difficult.
  • Sometimes an antihistamine with sedating effects may be given to reduce itching.
  • If necessary, administer analgesics such as paracetamol to relieve pain or discomfort.
  • Give cool drinks, preferably water, as frequently as possible.
  • Prevent secondary skin infection by keeping your child’s fingernails clean and short to minimise harm from scratching.

For fever: NEVER use aspirin or ibuprofen. Paracetamol is safe to use.

If a person who is at very high risk has been exposed to chicken pox, such as children with leukaemia or new-born babies of mothers with chicken pox, an immunoglobulin preparation known as varicella zoster immune globulin (VZIG) can be given by injection. This will provide immediate protection against chicken pox.

Importantly, VZIG may not prevent chicken pox unless given very early after exposure to an infected individual. It will, however, reduce the severity.

VZIG is prepared from blood donated by people with very high blood antibody levels to the chicken pox virus. In South Africa, it’s produced by the Kwa-Zulu Natal Blood Transfusion Service. As it’s scarce, it’s only available to those at great risk.

Fortunately, the anti-viral drug acylovir is effective and safe for the treatment of chicken pox. Any person who is at risk of severe chicken pox should be treated with acyclovir at the earliest sign of the disease. It can be used safely, even in very young babies.

Acyclovir can be given orally, but may be administered by intravenous infusion in serious situations, such as chicken pox pneumonia.

Because of the significantly increased risk of complications from chicken pox in adults, even if they’re healthy, some experts recommend that all people older than 18 years be treated with acyclovir within 24 hours of the start of the illness.

Acyclovir and newer drugs of this kind can also be of some benefit in reducing shingles symptoms.

Although, in principle, women should avoid most drugs in pregnancy, no adverse effects on the unborn child have been reported in pregnant women who have been treated with acyclovir. For this reason, the very significant risk to the pregnant mother should be the main consideration in deciding whether to treat chicken pox in pregnancy.

Unfortunately, there’s no proof as yet that treatment with acyclovir will protect the unborn baby from damage that may result from chicken pox infection in the first three months of pregnancy.

Chicken pox: when to call a doctor
It’s not usually necessary to ask a doctor to see a child with chicken pox. However, the following warrants a visit to your GP:

  • A very severe rash.
  • If bleeding occurs in the skin blisters.
  • If the chicken pox blisters occur in the mouth, and your child is unable to eat or drink.
  • If your child develops a persistent cough.
  • If your child complains of a headache.

Any adult who develops the typical rash of chicken pox must see a doctor as soon as possible.

How can chicken pox be prevented?
Previously, chicken pox was largely unavoidable. However, a safe, effective vaccine is now available. It’s in use as a routine childhood vaccination in many developed countries, notably the USA.

While the chicken pox vaccination (the varicella vaccine) is readily available in South Africa in private paediatric practice, it’s not yet routinely funded by the state as a childhood vaccination.

The vaccination is 95% effective in preventing chicken pox infection and it can be safely used in infants from 12 months of age. Ask your doctor about the chicken pox vaccine if your child hasn’t yet been infected.

Great care should still be taken to avoid exposing immune-compromised people (e.g. those who are malnourished, being treated for cancer or HIV positive) to anyone with chicken pox or anyone who has recently been in contact with chicken pox.

Following infection with the virus, a person is infectious from about 2 days before the rash develops until all the blisters have crusted, which usually takes about 6 to 7 days from the start of the rash.

In order not to infect others, avoid social contact while the chicken pox blisters are present. School-going children shouldn’t attend school until all their blisters have crusted and fallen off. It’s usually sufficient to stay home for one week.

Reviewed by paediatrician Prof Eugene Weinberg. MBChB; FCP (SA); PAED (SA). March 2018.

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