Chickenpox is one of the classic childhood diseases, and one of the most contagious. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts. Chickenpox is caused by a virus.

The virus that causes chickenpox is varicella-zoster, a member of the herpesvirus family. The same virus also causes herpes zoster (shingles) in adults.

In a typical scenario, a young child is covered in pox and out of school for a week. The first half of the week the child feels miserable from intense itching; the second half from boredom. Since the introduction of the chickenpox vaccine, classic chickenpox is much less common.

Chickenpox is extremely contagious, and can be spread by direct contact, droplet transmission, and airborne transmission. Even those with mild illness after the vaccine may be contagious.

When someone becomes infected, the pox usually appear 10 to 21 days later. People become contagious 1 to 2 days before breaking out with pox. They remain contagious while uncrusted blisters are present.

Once you catch chickenpox, the virus usually remains in your body for your lifetime, kept in check by the immune system. About 1 in 10 adults will experience shingles when the virus re-emerges during a period of stress.

Most cases of chickenpox occur in children younger than ten. The disease is usually mild, although serious complications sometimes occur. Adults and older children usually get sicker than younger children do.

Children under one year of age whose mothers have had chickenpox are not very likely to catch it. If they do, they often have mild cases because they retain partial immunity from their mothers' blood. Children under one year of age whose mothers have not had chickenpox, or whose inborn immunity has already waned, can get severe chickenpox.

The pox are worse in children who have other skin problems, such as eczema or a recent sunburn.

Complications are more common in those who are immunocompromised from an illness or medicines like chemotherapy. Some of the worst cases of chickenpox have been seen in children who have taken steroids during the incubation period, before they have any symptoms.

Most children with chickenpox act sick with vague symptoms, such as a fever, headache, tummy ache, or loss of appetite, for a day or two before breaking out in the classic pox rash. These symptoms last 2 to 4 days after breaking out.

The average child develops 250 to 500 small, itchy, fluid-filled blisters over red spots on the skin (“dew drops on a rose petal”). The blisters often appear first on the face, trunk, or scalp and spread from there. Appearance of the small blisters on the scalp, found in 80% of cases, clinches the diagnosis. After a day or two, the blisters become cloudy and then scab. Meanwhile, new crops of blisters spring up in groups. The pox often appear in the mouth, in the vagina, and on the eyelids. Children with skin problems such as eczema may get more than 1,500 pox.

Most pox will not leave scars unless they become contaminated with bacteria from scratching.

Some children who have had the vaccine will still develop a mild case of chickenpox. They usually recover much quicker and only have a few pox (< 30). These often do not follow the classic descriptions of the disease. However, these mild, post-vaccine cases are contagious.

Chickenpox is usually diagnosed from the classic rash and the child's medical history. Blood tests, and tests of the pox blisters themselves, can confirm the diagnosis if there is any question.

In most cases, it is enough to keep children comfortable while their own bodies fight the illness. Oatmeal baths in lukewarm water provide a crusty, comforting coating on the skin. An oral antihistamine can help to ease the itching, as can topical lotions. Lotions containing antihistamines are not proven more effective. Trim the fingernails short to reduce secondary infections and scarring.

Safe antiviral medicines have been developed. To be effective, they usually must be started within the first 24 hours of the rash. For most otherwise healthy children, the benefits of these medicines may not outweigh the costs. Adults and teens, at risk for more severe symptoms, may benefit if the case is seen early in its course

In addition, for those with skin conditions (such as eczema or recent sunburn), lung conditions (such as asthma), or those who have recently taken steroids, the antiviral medicines may be very important. The same is also true for adolescents and children who must take aspirin on an ongoing basis.

Some doctors also give antiviral medicines to people in the same household who subsequently come down with chickenpox. Because of their increased exposure, they would normally experience a more severe case of chickenpox.

DO NOT USE ASPIRIN for someone who may have chickenpox. Use of aspirin has been associated with Reyes Syndrome. Ibuprofen has been associated with more severe secondary infections. Acetaminophen may be used.

The outcome is generally excellent in uncomplicated cases. Encephalitis, pneumonia, and other invasive bacterial infections are serious, but rare, complications of chickenpox.

• Women who get chickenpox during pregnancy are at risk for congenital infection of the fetus.
• Newborns are at risk for severe infection, if they are exposed and their mothers are not immune.
• A secondary infection of the blisters may occur.
• Encephalitis is a serious, but rare complication.
• Reye's syndrome, pneumonia, myocarditis, and transient arthritis are other possible complications of chickenpox
• Cerebellar ataxia may appear during the recovery phase or later. This is characterized by a very unsteady walk.

Call your health care provider if you think that your child has chickenpox or if your child is over 12 months of age and has not been vaccinated against chickenpox.

Because chickenpox is airborne and very contagious before the rash appears, it is difficult to avoid. It is possible to catch chickenpox from someone on a different aisle in the supermarket, who doesn’t even know they have chickenpox!

A chickenpox vaccine is part of the routine immunization schedule. It is about 100% effective against moderate or severe illness, and 85-90% effective against mild chickenpox. Parents often express concern that the immunity from the vaccine might not last. The chickenpox vaccine, though, is the only routine vaccine that does not require a booster. However, a higher dose of the vaccine given later in life may reduce the incidence of herpes zoster (shingles). Reimmunization with the high dose is currently being considered by vaccination experts.

Talk to your doctor if you think your child might be at high risk for complications and might have been exposed. Immediate preventive measures may be important. Vaccine given early after exposure may still reduce the severity of the disease.

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American Academy of Pediatrics. Committee on Infectious Diseases. Varicella vaccine update.Pediatrics. 2000 Jan;105(1 Pt 1):136-41. Review.