Chicken pox is an infection caused by the varicella-zoster virus, one of the herpes viruses. Other herpes viruses include herpes simplex, that produces cold sores, and the Epstein-Barr virus that causes glandular fever.
It gets its name from the Latin word cicer, meaning chick peas because the spots were thought to look like chick peas on the skin. Like other herpes viruses, after the symptoms caused by the varicella-zoster virus have cleared up, the virus lies dormant in the body, but capable of reactivation. Varicella refers to its capacity to cause chicken pox and zoster to the reactivated form that causes shingles in later life.
Most children catch chicken pox in the pre-school or early school years. It is most common in winter and early spring, with widespread outbreaks most years. Only about 10% of people reach adult life without having been infected. The time between catching the infection and the appearance of the rash, (the incubation period) is usually about two weeks.
The rash, which is commonly the first sign of infection in children passes through four stages, from reddish spots flush with the skin surface, to raised papules, to small blisters filled with clear fluid (the vesicles), and, lastly, to pustules which crust over and heal. But the first thing most parents and children usually notice is an itchy rash consisting of multiple small blisters. Over the first few days, new crops of these vesicles appear, especially on the chest, back and face. Vesicles in the mouth, on the eye, and around the genital area and anus can be painful. Older children and adults are more likely to have a fever, headache, or muscle pains before rash breaks out. Generally, chicken pox caught in childhood is a milder illness that that caught as an adult.
How is it caught?
Chicken pox is very infectious. A child who has not yet had it before, and who comes into contact with an infected person, will almost certainly catch it. Children with chicken pox are infectious from about two days before to six days after the appearance of the rash, by which time the last crop of blisters should have crusted over.
The virus is spread either by direct contact with a person with active chicken pox or shingles, or by indirect contact with clothes or other articles infected with vesicle fluid, saliva, nasal discharge etc, or by airborne spread of small droplets of infected mucous or vesicle fluid.
To prevent further spread of chicken pox children should be kept off school for six to seven days until all the blisters have crusted over. Shingles cannot be caught from chicken pox.
Chicken pox is a miserable illness but is almost always harmless. Complications can, however, occur. The most common is a bacterial infection of the blisters. This should be treated promptly with antibiotics. Occasionally there is bleeding into the blisters due the to the virus interfering with blood clotting mechanisms. This is short-lasting and easily treated. In the recovery phase, some children may become clumsy and unable to walk properly. This is due to inflammation in a specific part of the brain. Although alarming, the symptoms will settle as the rash disappears. No treatment is needed and recovery will be complete. The varicella virus itself can cause a severe pneumonia. This can become life-threatening when complicated by additional bacterial infection but usually only occurs in adults.
There is about a two per cent risk of the varicella-zoster virus affecting the foetus if chicken pox is caught in early pregnancy. The greatest risk appears to be between the 13th and 20th week. In such an event the doctor will fully discuss the risks and how to determine if the baby has been harmed. If the mother has the first signs of the rash in the few days before or after delivery, the baby is at risk of developing severe chicken pox. This risk can be minimised by injecting the baby with varicella-zoster immunoglobulin. This is prepared from blood donors who have had chicken pox and whose blood thus contains high levels of antibody against the virus. Chicken pox in the second half of pregnancy, but before the last week, carries no risk to the baby.
Other groups at risk of severe complications from chicken pox are those with an impaired immune system. This includes patients receiving therapy for cancer and those on oral corticosteroid treatment (for example, people with severe asthma). If they have not had chicken pox before, these people must see their doctor immediately after any contact with the infection for appropriate treatment.
Chicken pox does not strike twice, except in very rare and unusual cases. One infection gives lifelong immunity.
Routine treatment for chicken pox aims to relieve the symptoms, as we know that it is generally a benign illness. The itchiness and irritation can be reduced by keeping the skin cool with light clothing and tepid baths or sponging. Calamine lotion applied to the spots, or antihistamine tablets may also help - ask your pharmacist for advice. Paracetamol or ibuprofen can be taken if the lesions are painful and will lower fever. Aspirin is generally not suitable for children under 12. It is especially unsuitable for children with chicken pox because the combination of chicken pox and aspirin can damage the liver. Although it can be difficult to resist, avoiding scratching spots as it can lead to scarring.
Specific antiviral treatment is available but only used in special circumstances, for example, for children being treated for leukaemia or other cancers.
The fever should settle within three to four days and the rash should then be showing signs of healing. New crops of vesicles are noticeably smaller and dont develop fully. If the fever persists, or the rash continues to spread significantly, or if there is a general reddening of the skin or some spots become angry and weeping, suggesting secondary infection, then see your doctor.
A varicella vaccine is available and is widely used in the USA. It is only used in the UK immunisation of children with leukaemia who have not had chicken pox before.
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
1. If I have chicken pox, when am I most infectious?
You're most infectious one or two days before the rash first appears. However, you remain infectious until the blisters crust over, which usually takes about five to six days. Stay away from school or work during this time.
The virus that causes chicken pox (varicella zoster) can be spread by the fine spray of saliva or mucous droplets when you cough or sneeze. You can also catch chicken pox through direct contact with the fluid from chicken pox blisters, either from a person who is infected or from items such as clothing that have been in contact with broken blisters.
Chicken pox is spread very easily. About nine out of 10 people who come into contact with someone carrying the virus will catch it if they haven't already had it.
It takes between one and three weeks after you have been exposed to the virus to develop chicken pox. This is called the incubation period.
2. Can I develop shingles after being exposed to someone with chicken pox?
No. However, if you haven't already had chicken pox, it's possible to catch it if you come into contact with someone who has shingles.
Even after your chicken pox infection clears, the virus that causes it (varicella zoster) remains in the nerves in your body.
Many years or even decades later, the varicella zoster virus can re-activate, causing shingles. The virus is most likely to re-activate if your immune system is weakened, for example by stress or a long-term course of corticosteroids. Shingles results in a very painful rash of small red raised spots. The rash develops on one side of your body and in one area, usually your chest.
The fluid in the blisters of people with shingles contains the varicella zoster virus. So if you come into contact with this fluid you can catch the virus if you haven't already had chickenpox.
In people with shingles the virus isn't spread by coughing or sneezing, so the infection isn't as contagious as chicken pox.
3. Can I travel on an aeroplane when I have chicken pox?
No. If you have chicken pox, air travel isn't allowed until the blisters have crusted over, as you may spread the infection to other passengers. This usually takes around six days.
Because chicken pox can be spread through the fine spray of droplets in the air from coughing or sneezing, travelling in a contained area such as an aeroplane puts other passengers at high risk of catching the virus.
You must wait for about six days after being infected, or until your last blister has burst and crusted over, before you fly. You should also check the airline policy and let your insurer know.
4. I have chicken pox. Is there anyone I should avoid, and for how long?
Yes. If you have chicken pox, there are certain people you should try to avoid while you're infectious. This includes people with a weakened immune system, pregnant woman and newborn babies, as they are more likely to have complications from chickenpox if they catch it.
If you have chicken pox, you're infectious about one or two days before the rash appears, up to when the blisters scab over, which is usually five or six days later.
Chicken pox can affect the development of an unborn baby, so it's important to avoid pregnant women who haven't had it before. People with weakened immune systems and babies are more likely to develop complications from chickenpox.
Because of these risks it's best not to go out in public when you have chicken pox, or to tell people you will come into contact with that you have chicken pox so they can let you know whether it's an issue.
5. What is the chicken pox vaccine and how does it work?
The chicken pox vaccine protects against the varicella zoster virus that causes chicken pox. The vaccine causes your immune system to produce antibodies that will help prevent chicken pox.
Vaccines stimulate your immune system in the same way as an infection, but without causing a full-blown disease. Vaccines are a safe way to ensure you develop your own antibodies to a particular infection.
The chicken pox vaccine (Varilrix or Varivax) contains a small amount of a weakened form of the varicella zoster virus that causes chicken pox. The vaccine causes your immune system to produce antibodies that will help protect against chicken pox.
The vaccine is given in two doses, four to eight weeks apart. Nine in 10 children and three-quarters of teenagers and adults who have the vaccine develop immunity against chickenpox.
The most common side-effect of the chicken pox vaccine is soreness and redness around the site of the injection. A mild rash may occur in one in 10 children and one in 20 adults.
6. Who can have the vaccine?
In the UK, the vaccine is currently only given to certain people, such as healthcare workers who are likely to come into contact with people who are particularly vulnerable to chicken pox (such as premature babies or people who have a weakened immune system, such as those who have HIV/AIDS, or those who are taking medicines that suppress the immune system). This is to protect vulnerable people from catching chicken pox from an infected carer.
Your doctor may recommend the vaccine if you haven't had chicken pox or shingles before trying for a baby or if you have a weakened immune system.
If you have an egg allergy, it's important that you tell your GP or practice nurse before having the vaccine.
7. Who shouldn't have the vaccine?
The chicken pox vaccine shouldn't be given to pregnant women. If you have the vaccine, you should wait three months after the last dose before trying for a baby.
You shouldn't have the vaccine if you are seriously unwell. It should be delayed until you recover and are in good health.
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